© 2013-2019 The original author(s).

Copies of this document may be made for your own use and for distribution to others, provided that you do not charge any fee for such copies and further provided that each copy contains this Copyright Notice, whether distributed in print or electronically.

Preface

The Spring Data Elasticsearch project applies core Spring concepts to the development of solutions using the Elasticsearch Search Engine. It provides:

  • Templates as a high-level abstraction for storing, searching, sorting documents and building aggregations.

  • Repositories which for example enable the user to express queries by defining interfaces having customized method names (for basic information about repositories see Working with Spring Data Repositories).

You will notice similarities to the Spring data solr and mongodb support in the Spring Framework.

1. What’s new

1.1. New in Spring Data Elasticsearch 4.0

  • Uses Spring 5.2.

  • Upgrade to Elasticsearch 7.5.1.

  • Deprecation of TransportClient usage.

  • Implements most of the mapping-types available for the index mappings.

  • Removal of the Jackson ObjectMapper, now using the MappingElasticsearchConverter

  • Cleanup of the API in the *Operations interfaces, grouping and renaming methods so that they match the Elasticsearch API, deprecating the old methods, aligning with other Spring Data modules.

  • Introduction of SearchHit<T> class to represent a found document together with the relevant result metadata for this document (i.e. sortValues).

  • Introduction of the SearchHits<T> class to represent a whole search result together with the metadata for the complete search result (i.e. max_score).

1.2. New in Spring Data Elasticsearch 3.2

2. Project Metadata

3. Requirements

Requires an installation of Elasticsearch.

3.1. Versions

The following table shows the Elasticsearch versions that are used by Spring Data release trains and version of Spring Data Elasticsearch included in that, as well as the Spring Boot versions refering to that particular Spring Data release train:

Spring Data Release Train Spring Data Elasticsearch Elasticsearch Spring Boot

Neumann[1]

4.0.x[1]

7.5.1

2.3.x[1]

Moore

3.2.x

6.8.4

2.2.x

Lovelace

3.1.x

6.2.2

2.1.x

Kay[2]

3.0.x[2]

5.5.0

2.0.x[2]

Ingalls[2]

2.1.x[2]

2.4.0

1.5.x[2]

Support for upcoming versions of Elasticsearch is being tracked and general compatibility should be given assuming the usage of the high-level REST client. :leveloffset: +1 :spring-framework-docs: https://docs.spring.io/spring/docs/5.2.3.RELEASE/spring-framework-reference :spring-framework-javadoc: https://docs.spring.io/spring/docs/5.2.3.RELEASE/javadoc-api

Working with Spring Data Repositories

The goal of the Spring Data repository abstraction is to significantly reduce the amount of boilerplate code required to implement data access layers for various persistence stores.

Spring Data repository documentation and your module

This chapter explains the core concepts and interfaces of Spring Data repositories. The information in this chapter is pulled from the Spring Data Commons module. It uses the configuration and code samples for the Java Persistence API (JPA) module. You should adapt the XML namespace declaration and the types to be extended to the equivalents of the particular module that you use. “Namespace reference” covers XML configuration, which is supported across all Spring Data modules supporting the repository API. “Repository query keywords” covers the query method keywords supported by the repository abstraction in general. For detailed information on the specific features of your module, see the chapter on that module of this document.

4. Core concepts

The central interface in the Spring Data repository abstraction is Repository. It takes the domain class to manage as well as the ID type of the domain class as type arguments. This interface acts primarily as a marker interface to capture the types to work with and to help you to discover interfaces that extend this one. The CrudRepository provides sophisticated CRUD functionality for the entity class that is being managed.

Example 1. CrudRepository interface
public interface CrudRepository<T, ID> extends Repository<T, ID> {

  <S extends T> S save(S entity);      (1)

  Optional<T> findById(ID primaryKey); (2)

  Iterable<T> findAll();               (3)

  long count();                        (4)

  void delete(T entity);               (5)

  boolean existsById(ID primaryKey);   (6)

  // … more functionality omitted.
}
1 Saves the given entity.
2 Returns the entity identified by the given ID.
3 Returns all entities.
4 Returns the number of entities.
5 Deletes the given entity.
6 Indicates whether an entity with the given ID exists.
We also provide persistence technology-specific abstractions, such as JpaRepository or MongoRepository. Those interfaces extend CrudRepository and expose the capabilities of the underlying persistence technology in addition to the rather generic persistence technology-agnostic interfaces such as CrudRepository.

On top of the CrudRepository, there is a PagingAndSortingRepository abstraction that adds additional methods to ease paginated access to entities:

Example 2. PagingAndSortingRepository interface
public interface PagingAndSortingRepository<T, ID> extends CrudRepository<T, ID> {

  Iterable<T> findAll(Sort sort);

  Page<T> findAll(Pageable pageable);
}

To access the second page of User by a page size of 20, you could do something like the following:

PagingAndSortingRepository<User, Long> repository = // … get access to a bean
Page<User> users = repository.findAll(PageRequest.of(1, 20));

In addition to query methods, query derivation for both count and delete queries is available. The following list shows the interface definition for a derived count query:

Example 3. Derived Count Query
interface UserRepository extends CrudRepository<User, Long> {

  long countByLastname(String lastname);
}

The following list shows the interface definition for a derived delete query:

Example 4. Derived Delete Query
interface UserRepository extends CrudRepository<User, Long> {

  long deleteByLastname(String lastname);

  List<User> removeByLastname(String lastname);
}

5. Query methods

Standard CRUD functionality repositories usually have queries on the underlying datastore. With Spring Data, declaring those queries becomes a four-step process:

  1. Declare an interface extending Repository or one of its subinterfaces and type it to the domain class and ID type that it should handle, as shown in the following example:

    interface PersonRepository extends Repository<Person, Long> { … }

  2. Declare query methods on the interface.

    interface PersonRepository extends Repository<Person, Long> {
  List<Person> findByLastname(String lastname);
}

  3. Set up Spring to create proxy instances for those interfaces, either with JavaConfig or with XML configuration.

    1. To use Java configuration, create a class similar to the following:

      import org.springframework.data.jpa.repository.config.EnableJpaRepositories;

@EnableJpaRepositories
class Config { … }

    2. To use XML configuration, define a bean similar to the following:

      <?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
   xmlns:jpa="http://www.springframework.org/schema/data/jpa"
   xsi:schemaLocation="http://www.springframework.org/schema/beans
     https://www.springframework.org/schema/beans/spring-beans.xsd
     http://www.springframework.org/schema/data/jpa
     https://www.springframework.org/schema/data/jpa/spring-jpa.xsd">

   <jpa:repositories base-package="com.acme.repositories"/>

</beans>

    The JPA namespace is used in this example. If you use the repository abstraction for any other store, you need to change this to the appropriate namespace declaration of your store module. In other words, you should exchange jpa in favor of, for example, mongodb.

    + Also, note that the JavaConfig variant does not configure a package explicitly, because the package of the annotated class is used by default. To customize the package to scan, use one of the basePackage… attributes of the data-store-specific repository’s @Enable${store}Repositories-annotation.

  4. Inject the repository instance and use it, as shown in the following example:

    class SomeClient {

  private final PersonRepository repository;

  SomeClient(PersonRepository repository) {
    this.repository = repository;
  }

  void doSomething() {
    List<Person> persons = repository.findByLastname("Matthews");
  }
}

The sections that follow explain each step in detail:

6. Defining Repository Interfaces

First, define a domain class-specific repository interface. The interface must extend Repository and be typed to the domain class and an ID type. If you want to expose CRUD methods for that domain type, extend CrudRepository instead of Repository.

6.1. Fine-tuning Repository Definition

Typically, your repository interface extends Repository, CrudRepository, or PagingAndSortingRepository. Alternatively, if you do not want to extend Spring Data interfaces, you can also annotate your repository interface with @RepositoryDefinition. Extending CrudRepository exposes a complete set of methods to manipulate your entities. If you prefer to be selective about the methods being exposed, copy the methods you want to expose from CrudRepository into your domain repository.

Doing so lets you define your own abstractions on top of the provided Spring Data Repositories functionality.

The following example shows how to selectively expose CRUD methods (findById and save, in this case):

Example 5. Selectively exposing CRUD methods
@NoRepositoryBean
interface MyBaseRepository<T, ID> extends Repository<T, ID> {

  Optional<T> findById(ID id);

  <S extends T> S save(S entity);
}

interface UserRepository extends MyBaseRepository<User, Long> {
  User findByEmailAddress(EmailAddress emailAddress);
}

In the prior example, you defined a common base interface for all your domain repositories and exposed findById(…) as well as save(…).These methods are routed into the base repository implementation of the store of your choice provided by Spring Data (for example, if you use JPA, the implementation is SimpleJpaRepository), because they match the method signatures in CrudRepository. So the UserRepository can now save users, find individual users by ID, and trigger a query to find Users by email address.

The intermediate repository interface is annotated with @NoRepositoryBean. Make sure you add that annotation to all repository interfaces for which Spring Data should not create instances at runtime.

6.2. Using Repositories with Multiple Spring Data Modules

Using a unique Spring Data module in your application makes things simple, because all repository interfaces in the defined scope are bound to the Spring Data module. Sometimes, applications require using more than one Spring Data module. In such cases, a repository definition must distinguish between persistence technologies. When it detects multiple repository factories on the class path, Spring Data enters strict repository configuration mode. Strict configuration uses details on the repository or the domain class to decide about Spring Data module binding for a repository definition:

  1. If the repository definition extends the module-specific repository, then it is a valid candidate for the particular Spring Data module.

  2. If the domain class is annotated with the module-specific type annotation, then it is a valid candidate for the particular Spring Data module. Spring Data modules accept either third-party annotations (such as JPA’s @Entity) or provide their own annotations (such as @Document for Spring Data MongoDB and Spring Data Elasticsearch).

The following example shows a repository that uses module-specific interfaces (JPA in this case):

Example 6. Repository definitions using module-specific interfaces
interface MyRepository extends JpaRepository<User, Long> { }

@NoRepositoryBean
interface MyBaseRepository<T, ID> extends JpaRepository<T, ID> { … }

interface UserRepository extends MyBaseRepository<User, Long> { … }

MyRepository and UserRepository extend JpaRepository in their type hierarchy. They are valid candidates for the Spring Data JPA module.

The following example shows a repository that uses generic interfaces:

Example 7. Repository definitions using generic interfaces
interface AmbiguousRepository extends Repository<User, Long> { … }

@NoRepositoryBean
interface MyBaseRepository<T, ID> extends CrudRepository<T, ID> { … }

interface AmbiguousUserRepository extends MyBaseRepository<User, Long> { … }

AmbiguousRepository and AmbiguousUserRepository extend only Repository and CrudRepository in their type hierarchy. While this is perfectly fine when using a unique Spring Data module, multiple modules cannot distinguish to which particular Spring Data these repositories should be bound.

The following example shows a repository that uses domain classes with annotations:

Example 8. Repository definitions using domain classes with annotations
interface PersonRepository extends Repository<Person, Long> { … }

@Entity
class Person { … }

interface UserRepository extends Repository<User, Long> { … }

@Document
class User { … }

PersonRepository references Person, which is annotated with the JPA @Entity annotation, so this repository clearly belongs to Spring Data JPA. UserRepository references User, which is annotated with Spring Data MongoDB’s @Document annotation.

The following bad example shows a repository that uses domain classes with mixed annotations:

Example 9. Repository definitions using domain classes with mixed annotations
interface JpaPersonRepository extends Repository<Person, Long> { … }

interface MongoDBPersonRepository extends Repository<Person, Long> { … }

@Entity
@Document
class Person { … }

This example shows a domain class using both JPA and Spring Data MongoDB annotations. It defines two repositories, JpaPersonRepository and MongoDBPersonRepository. One is intended for JPA and the other for MongoDB usage. Spring Data is no longer able to tell the repositories apart, which leads to undefined behavior.

Repository type details and distinguishing domain class annotations are used for strict repository configuration to identify repository candidates for a particular Spring Data module. Using multiple persistence technology-specific annotations on the same domain type is possible and enables reuse of domain types across multiple persistence technologies. However, Spring Data can then no longer determine a unique module with which to bind the repository.

The last way to distinguish repositories is by scoping repository base packages. Base packages define the starting points for scanning for repository interface definitions, which implies having repository definitions located in the appropriate packages. By default, annotation-driven configuration uses the package of the configuration class. The base package in XML-based configuration is mandatory.

The following example shows annotation-driven configuration of base packages:

Example 10. Annotation-driven configuration of base packages
@EnableJpaRepositories(basePackages = "com.acme.repositories.jpa")
@EnableMongoRepositories(basePackages = "com.acme.repositories.mongo")
class Configuration { … }

7. Defining Query Methods

The repository proxy has two ways to derive a store-specific query from the method name:

  • By deriving the query from the method name directly.

  • By using a manually defined query.

Available options depend on the actual store. However, there must be a strategy that decides what actual query is created. The next section describes the available options.

7.1. Query Lookup Strategies

The following strategies are available for the repository infrastructure to resolve the query. With XML configuration, you can configure the strategy at the namespace through the query-lookup-strategy attribute. For Java configuration, you can use the queryLookupStrategy attribute of the Enable${store}Repositories annotation. Some strategies may not be supported for particular datastores.

  • CREATE attempts to construct a store-specific query from the query method name. The general approach is to remove a given set of well known prefixes from the method name and parse the rest of the method. You can read more about query construction in “Query Creation”.

  • USE_DECLARED_QUERY tries to find a declared query and throws an exception if cannot find one. The query can be defined by an annotation somewhere or declared by other means. Consult the documentation of the specific store to find available options for that store. If the repository infrastructure does not find a declared query for the method at bootstrap time, it fails.

  • CREATE_IF_NOT_FOUND (default) combines CREATE and USE_DECLARED_QUERY. It looks up a declared query first, and, if no declared query is found, it creates a custom method name-based query. This is the default lookup strategy and, thus, is used if you do not configure anything explicitly. It allows quick query definition by method names but also custom-tuning of these queries by introducing declared queries as needed.

7.2. Query Creation

The query builder mechanism built into Spring Data repository infrastructure is useful for building constraining queries over entities of the repository. The mechanism strips the prefixes find…By, read…By, query…By, count…By, and get…By from the method and starts parsing the rest of it. The introducing clause can contain further expressions, such as a Distinct to set a distinct flag on the query to be created. However, the first By acts as delimiter to indicate the start of the actual criteria. At a very basic level, you can define conditions on entity properties and concatenate them with And and Or. The following example shows how to create a number of queries:

Example 11. Query creation from method names
interface PersonRepository extends Repository<Person, Long> {

  List<Person> findByEmailAddressAndLastname(EmailAddress emailAddress, String lastname);

  // Enables the distinct flag for the query
  List<Person> findDistinctPeopleByLastnameOrFirstname(String lastname, String firstname);
  List<Person> findPeopleDistinctByLastnameOrFirstname(String lastname, String firstname);

  // Enabling ignoring case for an individual property
  List<Person> findByLastnameIgnoreCase(String lastname);
  // Enabling ignoring case for all suitable properties
  List<Person> findByLastnameAndFirstnameAllIgnoreCase(String lastname, String firstname);

  // Enabling static ORDER BY for a query
  List<Person> findByLastnameOrderByFirstnameAsc(String lastname);
  List<Person> findByLastnameOrderByFirstnameDesc(String lastname);
}

The actual result of parsing the method depends on the persistence store for which you create the query. However, there are some general things to notice:

  • The expressions are usually property traversals combined with operators that can be concatenated. You can combine property expressions with AND and OR. You also get support for operators such as Between, LessThan, GreaterThan, and Like for the property expressions. The supported operators can vary by datastore, so consult the appropriate part of your reference documentation.

  • The method parser supports setting an IgnoreCase flag for individual properties (for example, findByLastnameIgnoreCase(…)) or for all properties of a type that supports ignoring case (usually String instances — for example, findByLastnameAndFirstnameAllIgnoreCase(…)). Whether ignoring cases is supported may vary by store, so consult the relevant sections in the reference documentation for the store-specific query method.

  • You can apply static ordering by appending an OrderBy clause to the query method that references a property and by providing a sorting direction (Asc or Desc). To create a query method that supports dynamic sorting, see “Special parameter handling”.

7.3. Property Expressions

Property expressions can refer only to a direct property of the managed entity, as shown in the preceding example. At query creation time, you already make sure that the parsed property is a property of the managed domain class. However, you can also define constraints by traversing nested properties. Consider the following method signature:

List<Person> findByAddressZipCode(ZipCode zipCode);

Assume a Person has an Address with a ZipCode. In that case, the method creates the property traversal x.address.zipCode. The resolution algorithm starts by interpreting the entire part (AddressZipCode) as the property and checks the domain class for a property with that name (uncapitalized). If the algorithm succeeds, it uses that property. If not, the algorithm splits up the source at the camel case parts from the right side into a head and a tail and tries to find the corresponding property — in our example, AddressZip and Code. If the algorithm finds a property with that head, it takes the tail and continues building the tree down from there, splitting the tail up in the way just described. If the first split does not match, the algorithm moves the split point to the left (Address, ZipCode) and continues.

Although this should work for most cases, it is possible for the algorithm to select the wrong property. Suppose the Person class has an addressZip property as well. The algorithm would match in the first split round already, choose the wrong property, and fail (as the type of addressZip probably has no code property).

To resolve this ambiguity you can use _ inside your method name to manually define traversal points. So our method name would be as follows:

List<Person> findByAddress_ZipCode(ZipCode zipCode);

Because we treat the underscore character as a reserved character, we strongly advise following standard Java naming conventions (that is, not using underscores in property names but using camel case instead).

7.4. Special parameter handling

To handle parameters in your query, define method parameters as already seen in the preceding examples. Besides that, the infrastructure recognizes certain specific types like Pageable and Sort, to apply pagination and sorting to your queries dynamically. The following example demonstrates these features:

Example 12. Using Pageable, Slice, and Sort in query methods
Page<User> findByLastname(String lastname, Pageable pageable);

Slice<User> findByLastname(String lastname, Pageable pageable);

List<User> findByLastname(String lastname, Sort sort);

List<User> findByLastname(String lastname, Pageable pageable);
APIs taking Sort and Pageable expect non-null values to be handed into methods. If you don’t want to apply any sorting or pagination use Sort.unsorted() and Pageable.unpaged().

The first method lets you pass an org.springframework.data.domain.Pageable instance to the query method to dynamically add paging to your statically defined query. A Page knows about the total number of elements and pages available. It does so by the infrastructure triggering a count query to calculate the overall number. As this might be expensive (depending on the store used), you can instead return a Slice. A Slice only knows about whether a next Slice is available, which might be sufficient when walking through a larger result set.

Sorting options are handled through the Pageable instance, too. If you only need sorting, add an org.springframework.data.domain.Sort parameter to your method. As you can see, returning a List is also possible. In this case, the additional metadata required to build the actual Page instance is not created (which, in turn, means that the additional count query that would have been necessary is not issued). Rather, it restricts the query to look up only the given range of entities.

To find out how many pages you get for an entire query, you have to trigger an additional count query. By default, this query is derived from the query you actually trigger.

7.4.1. Paging and Sorting

Simple sorting expressions can be defined by using property names. Expressions can be concatenated to collect multiple criterias into one expression.

Example 13. Defining sort expressions
Sort sort = Sort.by("firstname").ascending()
  .and(Sort.by("lastname").descending());

For a more type-safe way of defining sort expressions, start with the type to define the sort expression for and use method references to define the properties to sort on.

Example 14. Defining sort expressions using the type-safe API
TypedSort<Person> person = Sort.sort(Person.class);

TypedSort<Person> sort = person.by(Person::getFirstname).ascending()
  .and(person.by(Person::getLastname).descending());

If your store implementation supports Querydsl, you can also use the metamodel types generated to define sort expressions:

Example 15. Defining sort expressions using the Querydsl API
QSort sort = QSort.by(QPerson.firstname.asc())
  .and(QSort.by(QPerson.lastname.desc()));

7.5. Limiting Query Results

The results of query methods can be limited by using the first or top keywords, which can be used interchangeably. An optional numeric value can be appended to top or first to specify the maximum result size to be returned. If the number is left out, a result size of 1 is assumed. The following example shows how to limit the query size:

Example 16. Limiting the result size of a query with Top and First
User findFirstByOrderByLastnameAsc();

User findTopByOrderByAgeDesc();

Page<User> queryFirst10ByLastname(String lastname, Pageable pageable);

Slice<User> findTop3ByLastname(String lastname, Pageable pageable);

List<User> findFirst10ByLastname(String lastname, Sort sort);

List<User> findTop10ByLastname(String lastname, Pageable pageable);

The limiting expressions also support the Distinct keyword. Also, for the queries limiting the result set to one instance, wrapping the result into with the Optional keyword is supported.

If pagination or slicing is applied to a limiting query pagination (and the calculation of the number of pages available), it is applied within the limited result.

Limiting the results in combination with dynamic sorting by using a Sort parameter lets you express query methods for the 'K' smallest as well as for the 'K' biggest elements.

7.6. Repository Methods Returning Collections or Iterables

Query methods that return multiple results can use standard Java Iterable, List, Set. Beyond that we support returning Spring Data’s Streamable, a custom extension of Iterable, as well as collection types provided by Vavr.

7.6.1. Using Streamable as Query Method Return Type

Streamable can be used as alternative to Iterable or any collection type. It provides convenience methods to access a non-parallel Stream (missing from Iterable), the ability to directly ….filter(…) and ….map(…) over the elements and concatenate the Streamable to others:

Example 17. Using Streamable to combine query method results
interface PersonRepository extends Repository<Person, Long> {
  Streamable<Person> findByFirstnameContaining(String firstname);
  Streamable<Person> findByLastnameContaining(String lastname);
}

Streamable<Person> result = repository.findByFirstnameContaining("av")
  .and(repository.findByLastnameContaining("ea"));

7.6.2. Returning Custom Streamable Wrapper Types

Providing dedicated wrapper types for collections is a commonly used pattern to provide API on a query execution result that returns multiple elements. Usually these types are used by invoking a repository method returning a collection-like type and creating an instance of the wrapper type manually. That additional step can be avoided as Spring Data allows to use these wrapper types as query method return types if they meet the following criterias:

  1. The type implements Streamable.

  2. The type exposes either a constructor or a static factory method named of(…) or valueOf(…) taking Streamable as argument.

A sample use case looks as follows:

class Product { (1)
  MonetaryAmount getPrice() { … }
}

@RequiredArgConstructor(staticName = "of")
class Products implements Streamable<Product> { (2)

  private Streamable<Product> streamable;

  public MonetaryAmount getTotal() { (3)
    return streamable.stream() //
      .map(Priced::getPrice)
      .reduce(Money.of(0), MonetaryAmount::add);
  }
}

interface ProductRepository implements Repository<Product, Long> {
  Products findAllByDescriptionContaining(String text); (4)
}
1 A Product entity that exposes API to access the product’s price.
2 A wrapper type for a Streamable<Product> that can be constructed via Products.of(…) (factory method created via the Lombok annotation).
3 The wrapper type exposes additional API calculating new values on the Streamable<Product>.
4 That wrapper type can be used as query method return type directly. No need to return Stremable<Product> and manually wrap it in the repository client.

7.6.3. Support for Vavr Collections

Vavr is a library to embrace functional programming concepts in Java. It ships with a custom set of collection types that can be used as query method return types.

Vavr collection type Used Vavr implementation type Valid Java source types

io.vavr.collection.Seq

io.vavr.collection.List

java.util.Iterable

io.vavr.collection.Set

io.vavr.collection.LinkedHashSet

java.util.Iterable

io.vavr.collection.Map

io.vavr.collection.LinkedHashMap

java.util.Map

The types in the first column (or subtypes thereof) can be used as quer method return types and will get the types in the second column used as implementation type depending on the Java type of the actual query result (thrid column). Alternatively, Traversable (Vavr the Iterable equivalent) can be declared and we derive the implementation class from the actual return value, i.e. a java.util.List will be turned into a Vavr List/Seq, a java.util.Set becomes a Vavr LinkedHashSet/Set etc.

7.7. Null Handling of Repository Methods

As of Spring Data 2.0, repository CRUD methods that return an individual aggregate instance use Java 8’s Optional to indicate the potential absence of a value. Besides that, Spring Data supports returning the following wrapper types on query methods:

  • com.google.common.base.Optional

  • scala.Option

  • io.vavr.control.Option

Alternatively, query methods can choose not to use a wrapper type at all. The absence of a query result is then indicated by returning null. Repository methods returning collections, collection alternatives, wrappers, and streams are guaranteed never to return null but rather the corresponding empty representation. See “Repository query return types” for details.

7.7.1. Nullability Annotations

You can express nullability constraints for repository methods by using Spring Framework’s nullability annotations. They provide a tooling-friendly approach and opt-in null checks during runtime, as follows:

  • {spring-framework-javadoc}/org/springframework/lang/NonNullApi.html[@NonNullApi]: Used on the package level to declare that the default behavior for parameters and return values is to not accept or produce null values.

  • {spring-framework-javadoc}/org/springframework/lang/NonNull.html[@NonNull]: Used on a parameter or return value that must not be null (not needed on a parameter and return value where @NonNullApi applies).

  • {spring-framework-javadoc}/org/springframework/lang/Nullable.html[@Nullable]: Used on a parameter or return value that can be null.

Spring annotations are meta-annotated with JSR 305 annotations (a dormant but widely spread JSR). JSR 305 meta-annotations let tooling vendors such as IDEA, Eclipse, and Kotlin provide null-safety support in a generic way, without having to hard-code support for Spring annotations. To enable runtime checking of nullability constraints for query methods, you need to activate non-nullability on the package level by using Spring’s @NonNullApi in package-info.java, as shown in the following example:

Example 18. Declaring Non-nullability in package-info.java
@org.springframework.lang.NonNullApi
package com.acme;

Once non-null defaulting is in place, repository query method invocations get validated at runtime for nullability constraints. If a query execution result violates the defined constraint, an exception is thrown. This happens when the method would return null but is declared as non-nullable (the default with the annotation defined on the package the repository resides in). If you want to opt-in to nullable results again, selectively use @Nullable on individual methods. Using the result wrapper types mentioned at the start of this section continues to work as expected: An empty result is translated into the value that represents absence.

The following example shows a number of the techniques just described:

Example 19. Using different nullability constraints
package com.acme;                                                       (1)

import org.springframework.lang.Nullable;

interface UserRepository extends Repository<User, Long> {

  User getByEmailAddress(EmailAddress emailAddress);                    (2)

  @Nullable
  User findByEmailAddress(@Nullable EmailAddress emailAdress);          (3)

  Optional<User> findOptionalByEmailAddress(EmailAddress emailAddress); (4)
}
1 The repository resides in a package (or sub-package) for which we have defined non-null behavior.
2 Throws an EmptyResultDataAccessException when the query executed does not produce a result. Throws an IllegalArgumentException when the emailAddress handed to the method is null.
3 Returns null when the query executed does not produce a result. Also accepts null as the value for emailAddress.
4 Returns Optional.empty() when the query executed does not produce a result. Throws an IllegalArgumentException when the emailAddress handed to the method is null.

7.7.2. Nullability in Kotlin-based Repositories

Kotlin has the definition of nullability constraints baked into the language. Kotlin code compiles to bytecode, which does not express nullability constraints through method signatures but rather through compiled-in metadata. Make sure to include the kotlin-reflect JAR in your project to enable introspection of Kotlin’s nullability constraints. Spring Data repositories use the language mechanism to define those constraints to apply the same runtime checks, as follows:

Example 20. Using nullability constraints on Kotlin repositories
interface UserRepository : Repository<User, String> {

  fun findByUsername(username: String): User     (1)

  fun findByFirstname(firstname: String?): User? (2)
}
1 The method defines both the parameter and the result as non-nullable (the Kotlin default). The Kotlin compiler rejects method invocations that pass null to the method. If the query execution yields an empty result, an EmptyResultDataAccessException is thrown.
2 This method accepts null for the firstname parameter and returns null if the query execution does not produce a result.

7.8. Streaming query results

The results of query methods can be processed incrementally by using a Java 8 Stream<T> as return type. Instead of wrapping the query results in a Stream data store-specific methods are used to perform the streaming, as shown in the following example:

Example 21. Stream the result of a query with Java 8 Stream<T>
@Query("select u from User u")
Stream<User> findAllByCustomQueryAndStream();

Stream<User> readAllByFirstnameNotNull();

@Query("select u from User u")
Stream<User> streamAllPaged(Pageable pageable);
A Stream potentially wraps underlying data store-specific resources and must, therefore, be closed after usage. You can either manually close the Stream by using the close() method or by using a Java 7 try-with-resources block, as shown in the following example:
Example 22. Working with a Stream<T> result in a try-with-resources block
try (Stream<User> stream = repository.findAllByCustomQueryAndStream()) {
  stream.forEach(…);
}
Not all Spring Data modules currently support Stream<T> as a return type.

7.9. Async query results

Repository queries can be run asynchronously by using Spring’s asynchronous method execution capability. This means the method returns immediately upon invocation while the actual query execution occurs in a task that has been submitted to a Spring TaskExecutor. Asynchronous query execution is different from reactive query execution and should not be mixed. Refer to store-specific documentation for more details on reactive support. The following example shows a number of asynchronous queries:

@Async
Future<User> findByFirstname(String firstname);               (1)

@Async
CompletableFuture<User> findOneByFirstname(String firstname); (2)

@Async
ListenableFuture<User> findOneByLastname(String lastname);    (3)
1 Use java.util.concurrent.Future as the return type.
2 Use a Java 8 java.util.concurrent.CompletableFuture as the return type.
3 Use a org.springframework.util.concurrent.ListenableFuture as the return type.

8. Creating Repository Instances

In this section, you create instances and bean definitions for the defined repository interfaces. One way to do so is by using the Spring namespace that is shipped with each Spring Data module that supports the repository mechanism, although we generally recommend using Java configuration.

8.1. XML configuration

Each Spring Data module includes a repositories element that lets you define a base package that Spring scans for you, as shown in the following example:

Example 23. Enabling Spring Data repositories via XML
<?xml version="1.0" encoding="UTF-8"?>
<beans:beans xmlns:beans="http://www.springframework.org/schema/beans"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xmlns="http://www.springframework.org/schema/data/jpa"
  xsi:schemaLocation="http://www.springframework.org/schema/beans
    https://www.springframework.org/schema/beans/spring-beans.xsd
    http://www.springframework.org/schema/data/jpa
    https://www.springframework.org/schema/data/jpa/spring-jpa.xsd">

  <repositories base-package="com.acme.repositories" />

</beans:beans>

In the preceding example, Spring is instructed to scan com.acme.repositories and all its sub-packages for interfaces extending Repository or one of its sub-interfaces. For each interface found, the infrastructure registers the persistence technology-specific FactoryBean to create the appropriate proxies that handle invocations of the query methods. Each bean is registered under a bean name that is derived from the interface name, so an interface of UserRepository would be registered under userRepository. The base-package attribute allows wildcards so that you can define a pattern of scanned packages.

8.1.1. Using filters

By default, the infrastructure picks up every interface extending the persistence technology-specific Repository sub-interface located under the configured base package and creates a bean instance for it. However, you might want more fine-grained control over which interfaces have bean instances created for them. To do so, use <include-filter /> and <exclude-filter /> elements inside the <repositories /> element. The semantics are exactly equivalent to the elements in Spring’s context namespace. For details, see the Spring reference documentation for these elements.

For example, to exclude certain interfaces from instantiation as repository beans, you could use the following configuration:

Example 24. Using exclude-filter element
<repositories base-package="com.acme.repositories">
  <context:exclude-filter type="regex" expression=".*SomeRepository" />
</repositories>

The preceding example excludes all interfaces ending in SomeRepository from being instantiated.

8.2. JavaConfig

The repository infrastructure can also be triggered by using a store-specific @Enable${store}Repositories annotation on a JavaConfig class. For an introduction into Java-based configuration of the Spring container, see JavaConfig in the Spring reference documentation.

A sample configuration to enable Spring Data repositories resembles the following:

Example 25. Sample annotation based repository configuration
@Configuration
@EnableJpaRepositories("com.acme.repositories")
class ApplicationConfiguration {

  @Bean
  EntityManagerFactory entityManagerFactory() {
    // …
  }
}
The preceding example uses the JPA-specific annotation, which you would change according to the store module you actually use. The same applies to the definition of the EntityManagerFactory bean. See the sections covering the store-specific configuration.

8.3. Standalone usage

You can also use the repository infrastructure outside of a Spring container — for example, in CDI environments. You still need some Spring libraries in your classpath, but, generally, you can set up repositories programmatically as well. The Spring Data modules that provide repository support ship a persistence technology-specific RepositoryFactory that you can use as follows:

Example 26. Standalone usage of repository factory
RepositoryFactorySupport factory = … // Instantiate factory here
UserRepository repository = factory.getRepository(UserRepository.class);

9. Custom Implementations for Spring Data Repositories

This section covers repository customization and how fragments form a composite repository.

When a query method requires a different behavior or cannot be implemented by query derivation, then it is necessary to provide a custom implementation. Spring Data repositories let you provide custom repository code and integrate it with generic CRUD abstraction and query method functionality.

9.1. Customizing Individual Repositories

To enrich a repository with custom functionality, you must first define a fragment interface and an implementation for the custom functionality, as shown in the following example:

Example 27. Interface for custom repository functionality
interface CustomizedUserRepository {
  void someCustomMethod(User user);
}
Example 28. Implementation of custom repository functionality
class CustomizedUserRepositoryImpl implements CustomizedUserRepository {

  public void someCustomMethod(User user) {
    // Your custom implementation
  }
}
The most important part of the class name that corresponds to the fragment interface is the Impl postfix.

The implementation itself does not depend on Spring Data and can be a regular Spring bean. Consequently, you can use standard dependency injection behavior to inject references to other beans (such as a JdbcTemplate), take part in aspects, and so on.

Then you can let your repository interface extend the fragment interface, as shown in the following example:

Example 29. Changes to your repository interface
interface UserRepository extends CrudRepository<User, Long>, CustomizedUserRepository {

  // Declare query methods here
}

Extending the fragment interface with your repository interface combines the CRUD and custom functionality and makes it available to clients.

Spring Data repositories are implemented by using fragments that form a repository composition. Fragments are the base repository, functional aspects (such as QueryDsl), and custom interfaces along with their implementation. Each time you add an interface to your repository interface, you enhance the composition by adding a fragment. The base repository and repository aspect implementations are provided by each Spring Data module.

The following example shows custom interfaces and their implementations:

Example 30. Fragments with their implementations
interface HumanRepository {
  void someHumanMethod(User user);
}

class HumanRepositoryImpl implements HumanRepository {

  public void someHumanMethod(User user) {
    // Your custom implementation
  }
}

interface ContactRepository {

  void someContactMethod(User user);

  User anotherContactMethod(User user);
}

class ContactRepositoryImpl implements ContactRepository {

  public void someContactMethod(User user) {
    // Your custom implementation
  }

  public User anotherContactMethod(User user) {
    // Your custom implementation
  }
}

The following example shows the interface for a custom repository that extends CrudRepository:

Example 31. Changes to your repository interface
interface UserRepository extends CrudRepository<User, Long>, HumanRepository, ContactRepository {

  // Declare query methods here
}

Repositories may be composed of multiple custom implementations that are imported in the order of their declaration. Custom implementations have a higher priority than the base implementation and repository aspects. This ordering lets you override base repository and aspect methods and resolves ambiguity if two fragments contribute the same method signature. Repository fragments are not limited to use in a single repository interface. Multiple repositories may use a fragment interface, letting you reuse customizations across different repositories.

The following example shows a repository fragment and its implementation:

Example 32. Fragments overriding save(…)
interface CustomizedSave<T> {
  <S extends T> S save(S entity);
}

class CustomizedSaveImpl<T> implements CustomizedSave<T> {

  public <S extends T> S save(S entity) {
    // Your custom implementation
  }
}

The following example shows a repository that uses the preceding repository fragment:

Example 33. Customized repository interfaces
interface UserRepository extends CrudRepository<User, Long>, CustomizedSave<User> {
}

interface PersonRepository extends CrudRepository<Person, Long>, CustomizedSave<Person> {
}

9.1.1. Configuration

If you use namespace configuration, the repository infrastructure tries to autodetect custom implementation fragments by scanning for classes below the package in which it found a repository. These classes need to follow the naming convention of appending the namespace element’s repository-impl-postfix attribute to the fragment interface name. This postfix defaults to Impl. The following example shows a repository that uses the default postfix and a repository that sets a custom value for the postfix:

Example 34. Configuration example
<repositories base-package="com.acme.repository" />

<repositories base-package="com.acme.repository" repository-impl-postfix="MyPostfix" />

The first configuration in the preceding example tries to look up a class called com.acme.repository.CustomizedUserRepositoryImpl to act as a custom repository implementation. The second example tries to lookup com.acme.repository.CustomizedUserRepositoryMyPostfix.

Resolution of Ambiguity

If multiple implementations with matching class names are found in different packages, Spring Data uses the bean names to identify which one to use.

Given the following two custom implementations for the CustomizedUserRepository shown earlier, the first implementation is used. Its bean name is customizedUserRepositoryImpl, which matches that of the fragment interface (CustomizedUserRepository) plus the postfix Impl.

Example 35. Resolution of amibiguous implementations
package com.acme.impl.one;

class CustomizedUserRepositoryImpl implements CustomizedUserRepository {

  // Your custom implementation
}
package com.acme.impl.two;

@Component("specialCustomImpl")
class CustomizedUserRepositoryImpl implements CustomizedUserRepository {

  // Your custom implementation
}

If you annotate the UserRepository interface with @Component("specialCustom"), the bean name plus Impl then matches the one defined for the repository implementation in com.acme.impl.two, and it is used instead of the first one.

Manual Wiring

If your custom implementation uses annotation-based configuration and autowiring only, the preceding approach shown works well, because it is treated as any other Spring bean. If your implementation fragment bean needs special wiring, you can declare the bean and name it according to the conventions described in the preceding section. The infrastructure then refers to the manually defined bean definition by name instead of creating one itself. The following example shows how to manually wire a custom implementation:

Example 36. Manual wiring of custom implementations
<repositories base-package="com.acme.repository" />

<beans:bean id="userRepositoryImpl" class="…">
  <!-- further configuration -->
</beans:bean>

9.2. Customize the Base Repository

The approach described in the preceding section requires customization of each repository interfaces when you want to customize the base repository behavior so that all repositories are affected. To instead change behavior for all repositories, you can create an implementation that extends the persistence technology-specific repository base class. This class then acts as a custom base class for the repository proxies, as shown in the following example:

Example 37. Custom repository base class
class MyRepositoryImpl<T, ID>
  extends SimpleJpaRepository<T, ID> {

  private final EntityManager entityManager;

  MyRepositoryImpl(JpaEntityInformation entityInformation,
                          EntityManager entityManager) {
    super(entityInformation, entityManager);

    // Keep the EntityManager around to used from the newly introduced methods.
    this.entityManager = entityManager;
  }

  @Transactional
  public <S extends T> S save(S entity) {
    // implementation goes here
  }
}
The class needs to have a constructor of the super class which the store-specific repository factory implementation uses. If the repository base class has multiple constructors, override the one taking an EntityInformation plus a store specific infrastructure object (such as an EntityManager or a template class).

The final step is to make the Spring Data infrastructure aware of the customized repository base class. In Java configuration, you can do so by using the repositoryBaseClass attribute of the @Enable${store}Repositories annotation, as shown in the following example:

Example 38. Configuring a custom repository base class using JavaConfig
@Configuration
@EnableJpaRepositories(repositoryBaseClass = MyRepositoryImpl.class)
class ApplicationConfiguration { … }

A corresponding attribute is available in the XML namespace, as shown in the following example:

Example 39. Configuring a custom repository base class using XML
<repositories base-package="com.acme.repository"
     base-class="….MyRepositoryImpl" />

10. Publishing Events from Aggregate Roots

Entities managed by repositories are aggregate roots. In a Domain-Driven Design application, these aggregate roots usually publish domain events. Spring Data provides an annotation called @DomainEvents that you can use on a method of your aggregate root to make that publication as easy as possible, as shown in the following example:

Example 40. Exposing domain events from an aggregate root
class AnAggregateRoot {

    @DomainEvents (1)
    Collection<Object> domainEvents() {
        // … return events you want to get published here
    }

    @AfterDomainEventPublication (2)
    void callbackMethod() {
       // … potentially clean up domain events list
    }
}
1 The method using @DomainEvents can return either a single event instance or a collection of events. It must not take any arguments.
2 After all events have been published, we have a method annotated with @AfterDomainEventPublication. It can be used to potentially clean the list of events to be published (among other uses).

The methods are called every time one of a Spring Data repository’s save(…) methods is called.

11. Spring Data Extensions

This section documents a set of Spring Data extensions that enable Spring Data usage in a variety of contexts. Currently, most of the integration is targeted towards Spring MVC.

11.1. Querydsl Extension

Querydsl is a framework that enables the construction of statically typed SQL-like queries through its fluent API.

Several Spring Data modules offer integration with Querydsl through QuerydslPredicateExecutor, as shown in the following example:

Example 41. QuerydslPredicateExecutor interface
public interface QuerydslPredicateExecutor<T> {

  Optional<T> findById(Predicate predicate);  (1)

  Iterable<T> findAll(Predicate predicate);   (2)

  long count(Predicate predicate);            (3)

  boolean exists(Predicate predicate);        (4)

  // … more functionality omitted.
}
1 Finds and returns a single entity matching the Predicate.
2 Finds and returns all entities matching the Predicate.
3 Returns the number of entities matching the Predicate.
4 Returns whether an entity that matches the Predicate exists.

To make use of Querydsl support, extend QuerydslPredicateExecutor on your repository interface, as shown in the following example

Example 42. Querydsl integration on repositories
interface UserRepository extends CrudRepository<User, Long>, QuerydslPredicateExecutor<User> {
}

The preceding example lets you write typesafe queries using Querydsl Predicate instances, as shown in the following example:

Predicate predicate = user.firstname.equalsIgnoreCase("dave")
	.and(user.lastname.startsWithIgnoreCase("mathews"));

userRepository.findAll(predicate);

11.2. Web support

This section contains the documentation for the Spring Data web support as it is implemented in the current (and later) versions of Spring Data Commons. As the newly introduced support changes many things, we kept the documentation of the former behavior in [web.legacy].

Spring Data modules that support the repository programming model ship with a variety of web support. The web related components require Spring MVC JARs to be on the classpath. Some of them even provide integration with Spring HATEOAS. In general, the integration support is enabled by using the @EnableSpringDataWebSupport annotation in your JavaConfig configuration class, as shown in the following example:

Example 43. Enabling Spring Data web support
@Configuration
@EnableWebMvc
@EnableSpringDataWebSupport
class WebConfiguration {}

The @EnableSpringDataWebSupport annotation registers a few components we will discuss in a bit. It will also detect Spring HATEOAS on the classpath and register integration components for it as well if present.

Alternatively, if you use XML configuration, register either SpringDataWebConfiguration or HateoasAwareSpringDataWebConfiguration as Spring beans, as shown in the following example (for SpringDataWebConfiguration):

Example 44. Enabling Spring Data web support in XML
<bean class="org.springframework.data.web.config.SpringDataWebConfiguration" />

<!-- If you use Spring HATEOAS, register this one *instead* of the former -->
<bean class="org.springframework.data.web.config.HateoasAwareSpringDataWebConfiguration" />

11.2.1. Basic Web Support

The configuration shown in the previous section registers a few basic components:

  • A DomainClassConverter to let Spring MVC resolve instances of repository-managed domain classes from request parameters or path variables.

  • HandlerMethodArgumentResolver implementations to let Spring MVC resolve Pageable and Sort instances from request parameters.

DomainClassConverter

The DomainClassConverter lets you use domain types in your Spring MVC controller method signatures directly, so that you need not manually lookup the instances through the repository, as shown in the following example:

Example 45. A Spring MVC controller using domain types in method signatures
@Controller
@RequestMapping("/users")
class UserController {

  @RequestMapping("/{id}")
  String showUserForm(@PathVariable("id") User user, Model model) {

    model.addAttribute("user", user);
    return "userForm";
  }
}

As you can see, the method receives a User instance directly, and no further lookup is necessary. The instance can be resolved by letting Spring MVC convert the path variable into the id type of the domain class first and eventually access the instance through calling findById(…) on the repository instance registered for the domain type.

Currently, the repository has to implement CrudRepository to be eligible to be discovered for conversion.
HandlerMethodArgumentResolvers for Pageable and Sort

The configuration snippet shown in the previous section also registers a PageableHandlerMethodArgumentResolver as well as an instance of SortHandlerMethodArgumentResolver. The registration enables Pageable and Sort as valid controller method arguments, as shown in the following example:

Example 46. Using Pageable as controller method argument
@Controller
@RequestMapping("/users")
class UserController {

  private final UserRepository repository;

  UserController(UserRepository repository) {
    this.repository = repository;
  }

  @RequestMapping
  String showUsers(Model model, Pageable pageable) {

    model.addAttribute("users", repository.findAll(pageable));
    return "users";
  }
}

The preceding method signature causes Spring MVC try to derive a Pageable instance from the request parameters by using the following default configuration:

Table 1. Request parameters evaluated for Pageable instances

page

Page you want to retrieve. 0-indexed and defaults to 0.

size

Size of the page you want to retrieve. Defaults to 20.

sort

Properties that should be sorted by in the format property,property(,ASC|DESC). Default sort direction is ascending. Use multiple sort parameters if you want to switch directions — for example, ?sort=firstname&sort=lastname,asc.

To customize this behavior, register a bean implementing the PageableHandlerMethodArgumentResolverCustomizer interface or the SortHandlerMethodArgumentResolverCustomizer interface, respectively. Its customize() method gets called, letting you change settings, as shown in the following example:

@Bean SortHandlerMethodArgumentResolverCustomizer sortCustomizer() {
    return s -> s.setPropertyDelimiter("<-->");
}

If setting the properties of an existing MethodArgumentResolver is not sufficient for your purpose, extend either SpringDataWebConfiguration or the HATEOAS-enabled equivalent, override the pageableResolver() or sortResolver() methods, and import your customized configuration file instead of using the @Enable annotation.

If you need multiple Pageable or Sort instances to be resolved from the request (for multiple tables, for example), you can use Spring’s @Qualifier annotation to distinguish one from another. The request parameters then have to be prefixed with ${qualifier}_. The followig example shows the resulting method signature:

String showUsers(Model model,
      @Qualifier("thing1") Pageable first,
      @Qualifier("thing2") Pageable second) { … }

you have to populate thing1_page and thing2_page and so on.

The default Pageable passed into the method is equivalent to a PageRequest.of(0, 20) but can be customized by using the @PageableDefault annotation on the Pageable parameter.

11.2.2. Hypermedia Support for Pageables

Spring HATEOAS ships with a representation model class (PagedResources) that allows enriching the content of a Page instance with the necessary Page metadata as well as links to let the clients easily navigate the pages. The conversion of a Page to a PagedResources is done by an implementation of the Spring HATEOAS ResourceAssembler interface, called the PagedResourcesAssembler. The following example shows how to use a PagedResourcesAssembler as a controller method argument:

Example 47. Using a PagedResourcesAssembler as controller method argument
@Controller
class PersonController {

  @Autowired PersonRepository repository;

  @RequestMapping(value = "/persons", method = RequestMethod.GET)
  HttpEntity<PagedResources<Person>> persons(Pageable pageable,
    PagedResourcesAssembler assembler) {

    Page<Person> persons = repository.findAll(pageable);
    return new ResponseEntity<>(assembler.toResources(persons), HttpStatus.OK);
  }
}

Enabling the configuration as shown in the preceding example lets the PagedResourcesAssembler be used as a controller method argument. Calling toResources(…) on it has the following effects:

  • The content of the Page becomes the content of the PagedResources instance.

  • The PagedResources object gets a PageMetadata instance attached, and it is populated with information from the Page and the underlying PageRequest.

  • The PagedResources may get prev and next links attached, depending on the page’s state. The links point to the URI to which the method maps. The pagination parameters added to the method match the setup of the PageableHandlerMethodArgumentResolver to make sure the links can be resolved later.

Assume we have 30 Person instances in the database. You can now trigger a request (GET http://localhost:8080/persons) and see output similar to the following:

{ "links" : [ { "rel" : "next",
                "href" : "http://localhost:8080/persons?page=1&size=20 }
  ],
  "content" : [
     … // 20 Person instances rendered here
  ],
  "pageMetadata" : {
    "size" : 20,
    "totalElements" : 30,
    "totalPages" : 2,
    "number" : 0
  }
}

You see that the assembler produced the correct URI and also picked up the default configuration to resolve the parameters into a Pageable for an upcoming request. This means that, if you change that configuration, the links automatically adhere to the change. By default, the assembler points to the controller method it was invoked in, but that can be customized by handing in a custom Link to be used as base to build the pagination links, which overloads the PagedResourcesAssembler.toResource(…) method.

11.2.3. Web Databinding Support

Spring Data projections (described in [projections]) can be used to bind incoming request payloads by either using JSONPath expressions (requires Jayway JsonPath or XPath expressions (requires XmlBeam), as shown in the following example:

Example 48. HTTP payload binding using JSONPath or XPath expressions
@ProjectedPayload
public interface UserPayload {

  @XBRead("//firstname")
  @JsonPath("$..firstname")
  String getFirstname();

  @XBRead("/lastname")
  @JsonPath({ "$.lastname", "$.user.lastname" })
  String getLastname();
}

The type shown in the preceding example can be used as a Spring MVC handler method argument or by using ParameterizedTypeReference on one of RestTemplate's methods. The preceding method declarations would try to find firstname anywhere in the given document. The lastname XML lookup is performed on the top-level of the incoming document. The JSON variant of that tries a top-level lastname first but also tries lastname nested in a user sub-document if the former does not return a value. That way, changes in the structure of the source document can be mitigated easily without having clients calling the exposed methods (usually a drawback of class-based payload binding).

Nested projections are supported as described in [projections]. If the method returns a complex, non-interface type, a Jackson ObjectMapper is used to map the final value.

For Spring MVC, the necessary converters are registered automatically as soon as @EnableSpringDataWebSupport is active and the required dependencies are available on the classpath. For usage with RestTemplate, register a ProjectingJackson2HttpMessageConverter (JSON) or XmlBeamHttpMessageConverter manually.

For more information, see the web projection example in the canonical Spring Data Examples repository.

11.2.4. Querydsl Web Support

For those stores having QueryDSL integration, it is possible to derive queries from the attributes contained in a Request query string.

Consider the following query string:

?firstname=Dave&lastname=Matthews

Given the User object from previous examples, a query string can be resolved to the following value by using the QuerydslPredicateArgumentResolver.

QUser.user.firstname.eq("Dave").and(QUser.user.lastname.eq("Matthews"))
The feature is automatically enabled, along with @EnableSpringDataWebSupport, when Querydsl is found on the classpath.

Adding a @QuerydslPredicate to the method signature provides a ready-to-use Predicate, which can be run by using the QuerydslPredicateExecutor.

Type information is typically resolved from the method’s return type. Since that information does not necessarily match the domain type, it might be a good idea to use the root attribute of QuerydslPredicate.

The following exampe shows how to use @QuerydslPredicate in a method signature:

@Controller
class UserController {

  @Autowired UserRepository repository;

  @RequestMapping(value = "/", method = RequestMethod.GET)
  String index(Model model, @QuerydslPredicate(root = User.class) Predicate predicate,    (1)
          Pageable pageable, @RequestParam MultiValueMap<String, String> parameters) {

    model.addAttribute("users", repository.findAll(predicate, pageable));

    return "index";
  }
}
1 Resolve query string arguments to matching Predicate for User.

The default binding is as follows:

  • Object on simple properties as eq.

  • Object on collection like properties as contains.

  • Collection on simple properties as in.

Those bindings can be customized through the bindings attribute of @QuerydslPredicate or by making use of Java 8 default methods and adding the QuerydslBinderCustomizer method to the repository interface.

interface UserRepository extends CrudRepository<User, String>,
                                 QuerydslPredicateExecutor<User>,                (1)
                                 QuerydslBinderCustomizer<QUser> {               (2)

  @Override
  default void customize(QuerydslBindings bindings, QUser user) {

    bindings.bind(user.username).first((path, value) -> path.contains(value))    (3)
    bindings.bind(String.class)
      .first((StringPath path, String value) -> path.containsIgnoreCase(value)); (4)
    bindings.excluding(user.password);                                           (5)
  }
}
1 QuerydslPredicateExecutor provides access to specific finder methods for Predicate.
2 QuerydslBinderCustomizer defined on the repository interface is automatically picked up and shortcuts @QuerydslPredicate(bindings=…​).
3 Define the binding for the username property to be a simple contains binding.
4 Define the default binding for String properties to be a case-insensitive contains match.
5 Exclude the password property from Predicate resolution.

11.3. Repository Populators

If you work with the Spring JDBC module, you are probably familiar with the support to populate a DataSource with SQL scripts. A similar abstraction is available on the repositories level, although it does not use SQL as the data definition language because it must be store-independent. Thus, the populators support XML (through Spring’s OXM abstraction) and JSON (through Jackson) to define data with which to populate the repositories.

Assume you have a file data.json with the following content:

Example 49. Data defined in JSON
[ { "_class" : "com.acme.Person",
 "firstname" : "Dave",
  "lastname" : "Matthews" },
  { "_class" : "com.acme.Person",
 "firstname" : "Carter",
  "lastname" : "Beauford" } ]

You can populate your repositories by using the populator elements of the repository namespace provided in Spring Data Commons. To populate the preceding data to your PersonRepository, declare a populator similar to the following:

Example 50. Declaring a Jackson repository populator
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xmlns:repository="http://www.springframework.org/schema/data/repository"
  xsi:schemaLocation="http://www.springframework.org/schema/beans
    https://www.springframework.org/schema/beans/spring-beans.xsd
    http://www.springframework.org/schema/data/repository
    https://www.springframework.org/schema/data/repository/spring-repository.xsd">

  <repository:jackson2-populator locations="classpath:data.json" />

</beans>

The preceding declaration causes the data.json file to be read and deserialized by a Jackson ObjectMapper.

The type to which the JSON object is unmarshalled is determined by inspecting the _class attribute of the JSON document. The infrastructure eventually selects the appropriate repository to handle the object that was deserialized.

To instead use XML to define the data the repositories should be populated with, you can use the unmarshaller-populator element. You configure it to use one of the XML marshaller options available in Spring OXM. See the Spring reference documentation for details. The following example shows how to unmarshal a repository populator with JAXB:

Example 51. Declaring an unmarshalling repository populator (using JAXB)
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xmlns:repository="http://www.springframework.org/schema/data/repository"
  xmlns:oxm="http://www.springframework.org/schema/oxm"
  xsi:schemaLocation="http://www.springframework.org/schema/beans
    https://www.springframework.org/schema/beans/spring-beans.xsd
    http://www.springframework.org/schema/data/repository
    https://www.springframework.org/schema/data/repository/spring-repository.xsd
    http://www.springframework.org/schema/oxm
    https://www.springframework.org/schema/oxm/spring-oxm.xsd">

  <repository:unmarshaller-populator locations="classpath:data.json"
    unmarshaller-ref="unmarshaller" />

  <oxm:jaxb2-marshaller contextPath="com.acme" />

</beans>
Reference Documentation

Elasticsearch Clients

This chapter illustrates configuration and usage of supported Elasticsearch client implementations.

Spring Data Elasticsearch operates upon an Elasticsearch client that is connected to a single Elasticsearch node or a cluster. Although the Elasticsearch Client can be used to work with the cluster, applications using Spring Data Elasticsearch normally use the higher level abstractions of Elasticsearch Operations and Elasticsearch Repositories.

12. Transport Client

The well known TransportClient is deprecated as of Elasticsearch 7 and will be removed in Elasticsearch 8. (see the Elasticsearch documentation). Spring Data Elasticsearch will support the TransportClient as long as it is available in the used Elasticsearch version but has deprecated the classes using it since version 4.0.

We strongly recommend to use the High Level REST Client instead of the TransportClient.

Example 52. Transport Client
@Configuration
public class TransportClientConfig extends ElasticsearchConfigurationSupport {

    @Bean
    public Client elasticsearchClient() throws UnknownHostException {
        Settings settings = Settings.builder().put("cluster.name", "elasticsearch").build();        (1)
        TransportClient client = new PreBuiltTransportClient(settings);
        client.addTransportAddress(new TransportAddress(InetAddress.getByName("127.0.0.1"), 9300)); (2)
        return client;
    }

    @Bean(name = { "elasticsearchOperations", "elasticsearchTemplate" })
    public ElasticsearchTemplate elasticsearchTemplate() throws UnknownHostException {
        return new ElasticsearchTemplate(elasticsearchClient());
    }
}

// ...

IndexRequest request = new IndexRequest("spring-data", "elasticsearch", randomID())
 .source(someObject)
 .setRefreshPolicy(IMMEDIATE);

IndexResponse response = client.index(request);
1 The TransportClient must be configured with the cluster name.
2 The host and port to connect the client to.

13. High Level REST Client

The Java High Level REST Client is the default client of Elasticsearch, it provides a straight forward replacement for the TransportClient as it accepts and returns the very same request/response objects and therefore depends on the Elasticsearch core project. Asynchronous calls are operated upon a client managed thread pool and require a callback to be notified when the request is done.

Example 53. High Level REST Client
@Configuration
public class RestClientConfig extends AbstractElasticsearchConfiguration {

    @Override
    @Bean
    public RestHighLevelClient elasticsearchClient() {

        final ClientConfiguration clientConfiguration = ClientConfiguration.builder()  (1)
            .connectedTo("localhost:9200")
            .build();

        return RestClients.create(clientConfiguration).rest();                         (2)
    }
}

// ...

  @Autowired
  RestHighLevelClient highLevelClient;

  RestClient lowLevelClient = highLevelClient.lowLevelClient();                        (3)

// ...

IndexRequest request = new IndexRequest("spring-data", "elasticsearch", randomID())
  .source(singletonMap("feature", "high-level-rest-client"))
  .setRefreshPolicy(IMMEDIATE);

IndexResponse response = highLevelClient.index(request);
1 Use the builder to provide cluster addresses, set default HttpHeaders or enable SSL.
2 Create the RestHighLevelClient.
3 It is also possible to obtain the lowLevelRest() client.

14. Reactive Client

The ReactiveElasticsearchClient is a non official driver based on WebClient. It uses the request/response objects provided by the Elasticsearch core project. Calls are directly operated on the reactive stack, not wrapping async (thread pool bound) responses into reactive types.

Example 54. Reactive REST Client
static class Config {

  @Bean
  ReactiveElasticsearchClient client() {

    ClientConfiguration clientConfiguration = ClientConfiguration.builder()   (1)
      .connectedTo("localhost:9200", "localhost:9291")
      .withWebClientConfigurer(webClient -> {                                 (2)
        ExchangeStrategies exchangeStrategies = ExchangeStrategies.builder()
            .codecs(configurer -> configurer.defaultCodecs()
                .maxInMemorySize(-1))
            .build();
        return webClient.mutate().exchangeStrategies(exchangeStrategies).build();
       })
      .build();

    return ReactiveRestClients.create(clientConfiguration);
  }
}

// ...

Mono<IndexResponse> response = client.index(request ->

  request.index("spring-data")
    .type("elasticsearch")
    .id(randomID())
    .source(singletonMap("feature", "reactive-client"))
    .setRefreshPolicy(IMMEDIATE);
);
1 Use the builder to provide cluster addresses, set default HttpHeaders or enable SSL.
2 when configuring a reactive client, the withWebClientConfigurer hook can be used to customize the WebClient.
The ReactiveClient response, especially for search operations, is bound to the from (offset) & size (limit) options of the request.

15. Client Configuration

Client behaviour can be changed via the ClientConfiguration that allows to set options for SSL, connect and socket timeouts.

Example 55. Client Configuration
// optional if Basic Auhtentication is needed
HttpHeaders httpHeaders = new HttpHeaders();
httpHeaders.add("es-security-runas-user", "some-user")                  (1)

ClientConfiguration clientConfiguration = ClientConfiguration.builder()
  .connectedTo("localhost:9200", "localhost:9291")                      (2)
  .withProxy("localhost:8888")                                          (3)
  .withPathPrefix("ela")                                                (4)
  .withConnectTimeout(Duration.ofSeconds(5))                            (5)
  .withSocketTimeout(Duration.ofSeconds(3))                             (6)
  .useSsl()                                                             (7)
  .withDefaultHeaders(defaultHeaders)                                   (8)
  .withBasicAuth(username, password)                                    (9)
  . // ... other options
  .build();
1 Define default headers, if they need to be customized
2 Use the builder to provide cluster addresses, set default HttpHeaders or enable SSL.
3 Optionally set a proxy [3].
4 Optionally set a path prefix, mostly used when different clusters a behind some reverse proxy.
5 Set the connection timeout. Default is 10 sec.
6 Set the socket timeout. Default is 5 sec.
7 Optionally enable SSL.
8 Optionally set headers.
9 Add basic authentication.

16. Client Logging

To see what is actually sent to and received from the server Request / Response logging on the transport level needs to be turned on as outlined in the snippet below.

Enable transport layer logging
<logger name="org.springframework.data.elasticsearch.client.WIRE" level="trace"/>
The above applies to both the RestHighLevelClient and ReactiveElasticsearchClient when obtained via RestClients respectively ReactiveRestClients, is not available for the TransportClient.

Elasticsearch Object Mapping

Spring Data Elasticsearch Object Mapping is the process that maps a Java object - the domain entity - into the JSON representation that is stored in Elasticsearch and back.

Earlier versions of Spring Data Elasticsearch used a Jackson based conversion, Spring Data Elasticsearch 3.2.x introduced the Meta Model Object Mapping. As of version 4.0 only the Meta Object Mapping is used, the Jackson based mapper is not available anymore.

The main reasons for the removal of the Jackson based mapper are:

  • Custom mappings of fields needed to be done with annotations like @JsonFormat or @JsonInclude. This often caused problems when the same object was used in different JSON based datastores or sent over a JSON based API.

  • Custom field types and formats also need to be stored into the Elasticsearch index mappings. The Jackson based annotations did not fully provide all the information that is necessary to represent the types of Elasticsearch.

17. Meta Model Object Mapping

The Metamodel based approach uses domain type information for reading/writing from/to Elasticsearch. This allows to register Converter instances for specific domain type mapping.

17.1. Mapping Annotation Overview

The ElasticsearchEntityMapper can use metadata to drive the mapping of objects to documents. The metadata is taken from the entities properties which can be annotated.

The following annotations are available:

  • @Document: Applied at the class level to indicate this class is a candidate for mapping to the database. The most important attributes are:

    • indexName: the name of the index to store this entity in

    • type: the mapping type. If not set, the lowercased simple name of the class is used.

    • shards: the number of shards for the index.

    • replicas: the number of replicas for the index.

    • refreshIntervall: Refresh interval for the index. Used for index creation. Default value is "1s".

    • indexStoreType: Index storage type for the index. Used for index creation. Default value is "fs".

    • createIndex: Configuration whether to create an index on repository bootstrapping. Default value is true.

    • versionType: Configuration of version management. Default value is EXTERNAL.

  • @Id: Applied at the field level to mark the field used for identity purpose.

  • @Transient: By default all private fields are mapped to the document, this annotation excludes the field where it is applied from being stored in the database

  • @PersistenceConstructor: Marks a given constructor - even a package protected one - to use when instantiating the object from the database. Constructor arguments are mapped by name to the key values in the retrieved Document.

  • @Field: Applied at the field level and defines properties of the field, most of the attributes map to the respective Elasticsearch Mapping definitions:

    • name: The name of the field as it will be represented in the Elasticsearch document, if not set, the Java field name is used.

    • type: the field type, can be one of Text, Integer, Long, Date, Float, Double, Boolean, Object, Auto, Nested, Ip, Attachment, Keyword. See Elasticsearch Mapping Types

    • format and pattern custom definitions for the Date type.

    • store: Flag wether the original field value should be store in Elasticsearch, default value is false.

    • analyzer, searchAnalyzer, normalizer for specifying custom custom analyzers and normalizer.

    • copy_to: the target field to copy multiple document fields to.

  • @GeoPoint: marks a field as geo_point datatype. Can be omitted if the field is an instance of the GeoPoint class.

The mapping metadata infrastructure is defined in a separate spring-data-commons project that is technology agnostic.

17.2. Mapping Rules

17.2.1. Type Hints

Mapping uses type hints embedded in the document sent to the server to allow generic type mapping. Those type hints are represented as _class attributes within the document and are written for each aggregate root.

Example 56. Type Hints
public class Person {              (1)

  @Id String id;
  String firstname;
  String lastname;
}
{
  "_class" : "com.example.Person", (1)
  "id" : "cb7bef",
  "firstname" : "Sarah",
  "lastname" : "Connor"
}
1 By default the domain types class name is used for the type hint.

Type hints can be configured to hold custom information. Use the @TypeAlias annotation to do so.

Make sure to add types with @TypeAlias to the initial entity set (AbstractElasticsearchConfiguration#getInitialEntitySet) to already have entity information available when first reading data from the store.
Example 57. Type Hints with Alias
@TypeAlias("human")                (1)
public class Person {

  @Id String id;
  // ...
}
{
  "_class" : "human",              (1)
  "id" : ...
}
1 The configured alias is used when writing the entity.
Type hints will not be written for nested Objects unless the properties type is Object, an interface or the actual value type does not match the properties declaration.

17.2.2. Geospatial Types

Geospatial types like Point & GeoPoint are converted into lat/lon pairs.

Example 58. Geospatial types
public class Address {

  String city, street;
  Point location;
}
{
  "city" : "Los Angeles",
  "street" : "2800 East Observatory Road",
  "location" : { "lat" : 34.118347, "lon" : -118.3026284 }
}

17.2.3. Collections

For values inside Collections apply the same mapping rules as for aggregate roots when it comes to type hints and Custom Conversions.

Example 59. Collections
public class Person {

  // ...

  List<Person> friends;

}
{
  // ...

  "friends" : [ { "firstname" : "Kyle", "lastname" : "Reese" } ]
}

17.2.4. Maps

For values inside Maps apply the same mapping rules as for aggregate roots when it comes to type hints and Custom Conversions. However the Map key needs to a String to be processed by Elasticsearch.

Example 60. Collections
public class Person {

  // ...

  Map<String, Address> knownLocations;

}
{
  // ...

  "knownLocations" : {
    "arrivedAt" : {
       "city" : "Los Angeles",
       "street" : "2800 East Observatory Road",
       "location" : { "lat" : 34.118347, "lon" : -118.3026284 }
     }
  }
}

17.3. Custom Conversions

Looking at the Configuration from the previous section ElasticsearchCustomConversions allows registering specific rules for mapping domain and simple types.

Example 61. Meta Model Object Mapping Configuration
@Configuration
public class Config extends AbstractElasticsearchConfiguration {

  @Override
  public RestHighLevelClient elasticsearchClient() {
    return RestClients.create(ClientConfiguration.create("localhost:9200")).rest();
  }

  @Bean
  @Override
  public EntityMapper entityMapper() {

    ElasticsearchEntityMapper entityMapper = new ElasticsearchEntityMapper(
      elasticsearchMappingContext(), new DefaultConversionService());
    entityMapper.setConversions(elasticsearchCustomConversions());  (1)

  	return entityMapper;
  }

  @Bean
  @Override
  public ElasticsearchCustomConversions elasticsearchCustomConversions() {
    return new ElasticsearchCustomConversions(
      Arrays.asList(new AddressToMap(), new MapToAddress()));       (2)
  }

  @WritingConverter                                                 (3)
  static class AddressToMap implements Converter<Address, Map<String, Object>> {

    @Override
    public Map<String, Object> convert(Address source) {

      LinkedHashMap<String, Object> target = new LinkedHashMap<>();
      target.put("ciudad", source.getCity());
      // ...

      return target;
    }
  }

  @ReadingConverter                                                 (4)
  static class MapToAddress implements Converter<Map<String, Object>, Address> {

    @Override
    public Address convert(Map<String, Object> source) {

      // ...
      return address;
    }
  }
}
{
  "ciudad" : "Los Angeles",
  "calle" : "2800 East Observatory Road",
  "localidad" : { "lat" : 34.118347, "lon" : -118.3026284 }
}
1 Register ElasticsearchCustomConversions with the EntityMapper.
2 Add Converter implementations.
3 Set up the Converter used for writing DomainType to Elasticsearch.
4 Set up the Converter used for reading DomainType from search result.

Elasticsearch Operations

Spring Data Elasticsearch uses several interfaces to define the operations that can be called against an Elasticsearch index (for a description of the reactive interfaces see Reactive Elasticsearch Operations).

  • IndexOperations defines actions on index level like creating or deleting an index.

  • DocumentOperations defines actions to store, update and retrieve entities based on their id.

  • SearchOperations define the actions to search for multiple entities using queries

  • ElasticsearchOperations combines the DocumentOperations and SearchOperations interfaces.

These interfaces correspond to the structuring of the Elasticsearch API.

The default implementations of the interfaces offer:

  • index management functionality.

  • Read/Write mapping support for domain types.

  • A rich query and criteria api.

  • Resource management and Exception translation.

18. ElasticsearchTemplate

Usage of the ElasticsearchTemplate is deprecated as of version 4.0, use ElasticsearchRestTemplate instead.

The ElasticsearchTemplate is an implementation of the ElasticsearchOperations interface using the Transport Client.

Example 62. ElasticsearchTemplate configuration
@Configuration
public class TransportClientConfig extends ElasticsearchConfigurationSupport {

  @Bean
  public Client elasticsearchClient() throws UnknownHostException {                 (1)
    Settings settings = Settings.builder().put("cluster.name", "elasticsearch").build();
    TransportClient client = new PreBuiltTransportClient(settings);
    client.addTransportAddress(new TransportAddress(InetAddress.getByName("127.0.0.1"), 9300));
    return client;
  }

  @Bean(name = {"elasticsearchOperations", "elasticsearchTemplate"})
  public ElasticsearchTemplate elasticsearchTemplate() throws UnknownHostException { (2)
  	return new ElasticsearchTemplate(elasticsearchClient(), entityMapper());
  }
}
1 Setting up the Transport Client. Deprecated as of version 4.0.
2 Creating the ElasticsearchTemplate bean, offering both names, elasticsearchOperations and elasticsearchTemplate.

19. ElasticsearchRestTemplate

The ElasticsearchRestTemplate is an implementation of the ElasticsearchOperations interface using the High Level REST Client.

Example 63. ElasticsearchRestTemplate configuration
@Configuration
public class RestClientConfig extends AbstractElasticsearchConfiguration {
  @Override
  public RestHighLevelClient elasticsearchClient() {       (1)
    return RestClients.create(ClientConfiguration.localhost()).rest();
  }

  // no special bean creation needed                       (2)
}
1 Setting up the High Level REST Client.
2 The base class AbstractElasticsearchConfiguration already provides the elasticsearchTemplate bean.

20. Usage examples

As both ElasticsearchTemplate and ElasticsearchRestTemplate implement the ElasticsearchOperations interface, the code to use them is not different. The example shows how to use an injected ElasticsearchOperations instance in a Spring REST controller. The decision, if this is using the TransportClient or the RestClient is made by providing the corresponding Bean with one of the configurations shown above.

Example 64. ElasticsearchOperations usage
@RestController
@RequestMapping("/")
public class TestController {

  private  ElasticsearchOperations elasticsearchOperations;

  public TestController(ElasticsearchOperations elasticsearchOperations) { (1)
    this.elasticsearchOperations = elasticsearchOperations;
  }

  @PostMapping("/person")
  public String save(@RequestBody Person person) {                         (2)

    IndexQuery indexQuery = new IndexQueryBuilder()
      .withId(person.getId().toString())
      .withObject(person)
      .build();
    String documentId = elasticsearchOperations.index(indexQuery);
    return documentId;
  }

  @GetMapping("/person/{id}")
  public Person findById(@PathVariable("id")  Long id) {                   (3)
    Person person = elasticsearchOperations
      .queryForObject(GetQuery.getById(id.toString()), Person.class);
    return person;
  }
}
1 Let Spring inject the provided ElasticsearchOperations bean in the constructor.
2 Store some entity in the Elasticsearch cluster.
3 Retrieve the entity with a query by id.

To see the full possibilities of ElasticsearchOperations please refer to the API documentation.

21. Reactive Elasticsearch Operations

ReactiveElasticsearchOperations is the gateway to executing high level commands against an Elasticsearch cluster using the ReactiveElasticsearchClient.

The ReactiveElasticsearchTemplate is the default implementation of ReactiveElasticsearchOperations.

21.1. Reactive Elasticsearch Template

To get started the ReactiveElasticsearchTemplate needs to know about the actual client to work with. Please see Reactive Client for details on the client.

21.1.1. Reactive Template Configuration

The easiest way of setting up the ReactiveElasticsearchTemplate is via AbstractReactiveElasticsearchConfiguration providing dedicated configuration method hooks for base package, the initial entity set etc.

Example 65. The AbstractReactiveElasticsearchConfiguration
@Configuration
public class Config extends AbstractReactiveElasticsearchConfiguration {

  @Bean (1)
  @Override
  public ReactiveElasticsearchClient reactiveElasticsearchClient() {
      // ...
  }
}
1 Configure the client to use. This can be done by ReactiveRestClients or directly via DefaultReactiveElasticsearchClient.
If applicable set default HttpHeaders via the ClientConfiguration of the ReactiveElasticsearchClient. See Client Configuration.
If needed the ReactiveElasticsearchTemplate can be configured with default RefreshPolicy and IndicesOptions that get applied to the related requests by overriding the defaults of refreshPolicy() and indicesOptions().

However one might want to be more in control over the actual components and use a more verbose approach.

Example 66. Configure the ReactiveElasticsearchTemplate
@Configuration
public class Config {

  @Bean (1)
  public ReactiveElasticsearchClient reactiveElasticsearchClient() {
    // ...
  }
  @Bean (2)
  public ElasticsearchConverter elasticsearchConverter() {
    return new MappingElasticsearchConverter(elasticsearchMappingContext());
  }
  @Bean (3)
  public SimpleElasticsearchMappingContext elasticsearchMappingContext() {
    return new SimpleElasticsearchMappingContext();
  }
  @Bean (4)
  public ReactiveElasticsearchOperations reactiveElasticsearchOperations() {
    return new ReactiveElasticsearchTemplate(reactiveElasticsearchClient(), elasticsearchConverter());
  }
}
1 Configure the client to use. This can be done by ReactiveRestClients or directly via DefaultReactiveElasticsearchClient.
2 Set up the ElasticsearchConverter used for domain type mapping utilizing metadata provided by the mapping context.
3 The Elasticsearch specific mapping context for domain type metadata.
4 The actual template based on the client and conversion infrastructure.

21.1.2. Reactive Template Usage

ReactiveElasticsearchTemplate lets you save, find and delete your domain objects and map those objects to documents stored in Elasticsearch.

Consider the following:

Example 67. Use the ReactiveElasticsearchTemplate
@Document(indexName = "marvel")
public class Person {

  private @Id String id;
  private String name;
  private int age;
  // Getter/Setter omitted...
}
template.save(new Person("Bruce Banner", 42))                    (1)
  .doOnNext(System.out::println)
  .flatMap(person -> template.findById(person.id, Person.class)) (2)
  .doOnNext(System.out::println)
  .flatMap(person -> template.delete(person))                    (3)
  .doOnNext(System.out::println)
  .flatMap(id -> template.count(Person.class))                   (4)
  .doOnNext(System.out::println)
  .subscribe(); (5)

The above outputs the following sequence on the console.

> Person(id=QjWCWWcBXiLAnp77ksfR, name=Bruce Banner, age=42)
> Person(id=QjWCWWcBXiLAnp77ksfR, name=Bruce Banner, age=42)
> QjWCWWcBXiLAnp77ksfR
> 0
1 Insert a new Person document into the marvel index under type characters. The id is generated on server side and set into the instance returned.
2 Lookup the Person with matching id in the marvel index under type characters.
3 Delete the Person with matching id, extracted from the given instance, in the marvel index under type characters.
4 Count the total number of documents in the marvel index under type characters.
5 Don’t forget to subscribe().

22. Search Result Types

When a document is retrieved with the methods of the DocumentOperations interface, just the found entity will be returned. When searching with the methods of the SearchOperations interface, additional information is available for each entity, for example the score or the sortValues of the found entity.

In order to return this information, each entity is wrapped in a SearchHit object that contains this entity-specific additional information. These SearchHit objects themselves are returned within a SearchHits object which additionally contains informations about the whole search ike the maxScore or requested aggregations.

SearchHit<T>

Contains the following information:

  • Id

  • Score

  • Sort Values

  • Highligth fields

  • The retrieved entity of type <T>

SearchHits<T>

Contains the following information:

  • Number of total hits

  • Total hits relation

  • Maximum score

  • A list of SearchHit<T> objects

  • Returned aggregations

Elasticsearch Repositories

This chapter includes details of the Elasticsearch repository implementation.

23. Query methods

23.1. Query lookup strategies

The Elasticsearch module supports all basic query building feature as string queries, native search queries, criteria based queries or have it being derived from the method name.

23.1.1. Declared queries

Deriving the query from the method name is not always sufficient and/or may result in unreadable method names. In this case one might make use of the @Query annotation (see Using @Query Annotation ).

23.2. Query creation

Generally the query creation mechanism for Elasticsearch works as described in Query methods. Here’s a short example of what a Elasticsearch query method translates into:

Example 68. Query creation from method names
interface BookRepository extends Repository<Book, String> {
  List<Book> findByNameAndPrice(String name, Integer price);
}

The method name above will be translated into the following Elasticsearch json query

{
    "query": {
        "bool" : {
            "must" : [
                { "query_string" : { "query" : "?", "fields" : [ "name" ] } },
                { "query_string" : { "query" : "?", "fields" : [ "price" ] } }
            ]
        }
    }
}

A list of supported keywords for Elasticsearch is shown below.

Table 2. Supported keywords inside method names
Keyword Sample Elasticsearch Query String

And

findByNameAndPrice

{ "query" : { "bool" : { "must" : [ { "query_string" : { "query" : "?", "fields" : [ "name" ] } }, { "query_string" : { "query" : "?", "fields" : [ "price" ] } } ] } }}

Or

findByNameOrPrice

{ "query" : { "bool" : { "should" : [ { "query_string" : { "query" : "?", "fields" : [ "name" ] } }, { "query_string" : { "query" : "?", "fields" : [ "price" ] } } ] } }}

Is

findByName

{ "query" : { "bool" : { "must" : [ { "query_string" : { "query" : "?", "fields" : [ "name" ] } } ] } }}

Not

findByNameNot

{ "query" : { "bool" : { "must_not" : [ { "query_string" : { "query" : "?", "fields" : [ "name" ] } } ] } }}

Between

findByPriceBetween

{ "query" : { "bool" : { "must" : [ {"range" : {"price" : {"from" : ?, "to" : ?, "include_lower" : true, "include_upper" : true } } } ] } }}

LessThan

findByPriceLessThan

{ "query" : { "bool" : { "must" : [ {"range" : {"price" : {"from" : null, "to" : ?, "include_lower" : true, "include_upper" : false } } } ] } }}

LessThanEqual

findByPriceLessThanEqual

{ "query" : { "bool" : { "must" : [ {"range" : {"price" : {"from" : null, "to" : ?, "include_lower" : true, "include_upper" : true } } } ] } }}

GreaterThan

findByPriceGreaterThan

{ "query" : { "bool" : { "must" : [ {"range" : {"price" : {"from" : ?, "to" : null, "include_lower" : false, "include_upper" : true } } } ] } }}

GreaterThanEqual

findByPriceGreaterThan

{ "query" : { "bool" : { "must" : [ {"range" : {"price" : {"from" : ?, "to" : null, "include_lower" : true, "include_upper" : true } } } ] } }}

Before

findByPriceBefore

{ "query" : { "bool" : { "must" : [ {"range" : {"price" : {"from" : null, "to" : ?, "include_lower" : true, "include_upper" : true } } } ] } }}

After

findByPriceAfter

{ "query" : { "bool" : { "must" : [ {"range" : {"price" : {"from" : ?, "to" : null, "include_lower" : true, "include_upper" : true } } } ] } }}

Like

findByNameLike

{ "query" : { "bool" : { "must" : [ { "query_string" : { "query" : "?*", "fields" : [ "name" ] }, "analyze_wildcard": true } ] } }}

StartingWith

findByNameStartingWith

{ "query" : { "bool" : { "must" : [ { "query_string" : { "query" : "?*", "fields" : [ "name" ] }, "analyze_wildcard": true } ] } }}

EndingWith

findByNameEndingWith

{ "query" : { "bool" : { "must" : [ { "query_string" : { "query" : "*?", "fields" : [ "name" ] }, "analyze_wildcard": true } ] } }}

Contains/Containing

findByNameContaining

{ "query" : { "bool" : { "must" : [ { "query_string" : { "query" : "*?*", "fields" : [ "name" ] }, "analyze_wildcard": true } ] } }}

In

findByNameIn(Collection<String>names)

{ "query" : { "bool" : { "must" : [ {"bool" : {"must" : [ {"terms" : {"name" : ["?","?"]}} ] } } ] } }}

NotIn

findByNameNotIn(Collection<String>names)

{ "query" : { "bool" : { "must" : [ {"bool" : {"must_not" : [ {"terms" : {"name" : ["?","?"]}} ] } } ] } }}

Near

findByStoreNear

Not Supported Yet !

True

findByAvailableTrue

{ "query" : { "bool" : { "must" : [ { "query_string" : { "query" : "true", "fields" : [ "available" ] } } ] } }}

False

findByAvailableFalse

{ "query" : { "bool" : { "must" : [ { "query_string" : { "query" : "false", "fields" : [ "available" ] } } ] } }}

OrderBy

findByAvailableTrueOrderByNameDesc

{ "query" : { "bool" : { "must" : [ { "query_string" : { "query" : "true", "fields" : [ "available" ] } } ] } }, "sort":[{"name":{"order":"desc"}}] }

23.3. Method return types

Repository methods can be defined to have the following return types for returning multiple Elements:

  • List<T>

  • Stream<T>

  • SearchHits<T>

  • List<SearchHits<T>>

  • Stream<>>SearchHit<T>>

23.4. Using @Query Annotation

Example 69. Declare query at the method using the @Query annotation.
interface BookRepository extends ElasticsearchRepository<Book, String> {
    @Query("{\"bool\" : {\"must\" : {\"field\" : {\"name\" : \"?0\"}}}}")
    Page<Book> findByName(String name,Pageable pageable);
}

24. Annotation based configuration

The Spring Data Elasticsearch repositories support can be activated using an annotation through JavaConfig.

Example 70. Spring Data Elasticsearch repositories using JavaConfig
@Configuration
@EnableElasticsearchRepositories(                             (1)
  basePackages = "org.springframework.data.elasticsearch.repositories"
  )
static class Config {

  @Bean
  public ElasticsearchOperations elasticsearchTemplate() {    (2)
      // ...
  }
}

class ProductService {

  private ProductRepository repository;                       (3)

  public ProductService(ProductRepository repository) {
    this.repository = repository;
  }

  public Page<Product> findAvailableBookByName(String name, Pageable pageable) {
    return repository.findByAvailableTrueAndNameStartingWith(name, pageable);
  }
}
1 The EnableElasticsearchRepositories annotation activates the Repository support. If no base package is configured, it will use the one of the configuration class it is put on.
2 Provide a Bean named elasticsearchTemplate of type ElasticsearchOperations by using one of the configurations shown in the Elasticsearch Operations chapter.
3 Let Spring inject the Repository bean into your class.

25. Elasticsearch Repositories using CDI

The Spring Data Elasticsearch repositories can also be set up using CDI functionality.

Example 71. Spring Data Elasticsearch repositories using CDI
class ElasticsearchTemplateProducer {

  @Produces
  @ApplicationScoped
  public ElasticsearchOperations createElasticsearchTemplate() {
    // ...                               (1)
  }
}

class ProductService {

  private ProductRepository repository;  (2)
  public Page<Product> findAvailableBookByName(String name, Pageable pageable) {
    return repository.findByAvailableTrueAndNameStartingWith(name, pageable);
  }
  @Inject
  public void setRepository(ProductRepository repository) {
    this.repository = repository;
  }
}
1 Create a component by using the same calls as are used in the Elasticsearch Operations chapter.
2 Let the CDI framework inject the Repository into your class.

26. Spring Namespace

The Spring Data Elasticsearch module contains a custom namespace allowing definition of repository beans as well as elements for instantiating a ElasticsearchServer .

Using the repositories element looks up Spring Data repositories as described in Creating Repository Instances .

Example 72. Setting up Elasticsearch repositories using Namespace
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:elasticsearch="http://www.springframework.org/schema/data/elasticsearch"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
       https://www.springframework.org/schema/beans/spring-beans-3.1.xsd
       http://www.springframework.org/schema/data/elasticsearch
       https://www.springframework.org/schema/data/elasticsearch/spring-elasticsearch-1.0.xsd">

  <elasticsearch:repositories base-package="com.acme.repositories" />

</beans>

Using the Transport Client or Rest Client element registers an instance of Elasticsearch Server in the context.

Example 73. Transport Client using Namespace
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:elasticsearch="http://www.springframework.org/schema/data/elasticsearch"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
       https://www.springframework.org/schema/beans/spring-beans-3.1.xsd
       http://www.springframework.org/schema/data/elasticsearch
       https://www.springframework.org/schema/data/elasticsearch/spring-elasticsearch-1.0.xsd">

  <elasticsearch:transport-client id="client" cluster-nodes="localhost:9300,someip:9300" />

</beans>
Example 74. Rest Client using Namespace
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:elasticsearch="http://www.springframework.org/schema/data/elasticsearch"
       xsi:schemaLocation="http://www.springframework.org/schema/data/elasticsearch
       https://www.springframework.org/schema/data/elasticsearch/spring-elasticsearch.xsd
       http://www.springframework.org/schema/beans
       https://www.springframework.org/schema/beans/spring-beans.xsd">

  <elasticsearch:rest-client id="restClient" hosts="http://localhost:9200">

</beans>

27. Reactive Elasticsearch Repositories

Reactive Elasticsearch repository support builds on the core repository support explained in Working with Spring Data Repositories utilizing operations provided via Reactive Elasticsearch Operations executed by a Reactive Client.

Spring Data Elasticsearch reactive repository support uses Project Reactor as its reactive composition library of choice.

There are 3 main interfaces to be used:

  • ReactiveRepository

  • ReactiveCrudRepository

  • ReactiveSortingRepository

27.1. Usage

To access domain objects stored in a Elasticsearch using a Repository, just create an interface for it. Before you can actually go on and do that you will need an entity.

Example 75. Sample Person entity
public class Person {

  @Id
  private String id;
  private String firstname;
  private String lastname;
  private Address address;

  // … getters and setters omitted
}
Please note that the id property needs to be of type String.
Example 76. Basic repository interface to persist Person entities
interface ReactivePersonRepository extends ReactiveSortingRepository<Person, String> {

  Flux<Person> findByFirstname(String firstname);                                   (1)

  Flux<Person> findByFirstname(Publisher<String> firstname);                        (2)

  Flux<Person> findByFirstnameOrderByLastname(String firstname);                    (3)

  Flux<Person> findByFirstname(String firstname, Sort sort);                        (4)

  Flux<Person> findByFirstname(String firstname, Pageable page);                    (5)

  Mono<Person> findByFirstnameAndLastname(String firstname, String lastname);       (6)

  Mono<Person> findFirstByLastname(String lastname);                                (7)

  @Query("{ \"bool\" : { \"must\" : { \"term\" : { \"lastname\" : \"?0\" } } } }")
  Flux<Person> findByLastname(String lastname);                                     (8)

  Mono<Long> countByFirstname(String firstname)                                     (9)

  Mono<Boolean> existsByFirstname(String firstname)                                 (10)

  Mono<Long> deleteByFirstname(String firstname)                                    (11)
}
1 The method shows a query for all people with the given lastname.
2 Finder method awaiting input from Publisher to bind parameter value for firstname.
3 Finder method ordering matching documents by lastname.
4 Finder method ordering matching documents by the expression defined via the Sort parameter.
5 Use Pageable to pass offset and sorting parameters to the database.
6 Finder method concating criteria using And / Or keywords.
7 Find the first matching entity.
8 The method shows a query for all people with the given lastname looked up by running the annotated @Query with given parameters.
9 Count all entities with matching firstname.
10 Check if at least one entity with matching firstname exists.
11 Delete all entites with matching firstname.

27.2. Configuration

For Java configuration, use the @EnableReactiveElasticsearchRepositories annotation. If no base package is configured, the infrastructure scans the package of the annotated configuration class.

The following listing shows how to use Java configuration for a repository:

Example 77. Java configuration for repositories
@Configuration
@EnableReactiveElasticsearchRepositories
public class Config extends AbstractReactiveElasticsearchConfiguration {

  @Override
  public ReactiveElasticsearchClient reactiveElasticsearchClient() {
    return ReactiveRestClients.create(ClientConfiguration.localhost());
  }
}

Because the repository from the previous example extends ReactiveSortingRepository, all CRUD operations are available as well as methods for sorted access to the entities. Working with the repository instance is a matter of dependency injecting it into a client, as the following example shows:

Example 78. Sorted access to Person entities
public class PersonRepositoryTests {

  @Autowired ReactivePersonRepository repository;

  @Test
  public void sortsElementsCorrectly() {

    Flux<Person> persons = repository.findAll(Sort.by(new Order(ASC, "lastname")));

    // ...
  }
}

Miscellaneous Elasticsearch Operation Support

This chapter covers additional support for Elasticsearch operations that cannot be directly accessed via the repository interface. It is recommended to add those operations as custom implementation as described in Custom Implementations for Spring Data Repositories .

28. Filter Builder

Filter Builder improves query speed.

private ElasticsearchOperations operations;

IndexCoordinates index = IndexCoordinates.of("sample-index");

SearchQuery searchQuery = new NativeSearchQueryBuilder()
  .withQuery(matchAllQuery())
  .withFilter(boolFilter().must(termFilter("id", documentId)))
  .build();

Page<SampleEntity> sampleEntities = operations.searchForPage(searchQuery, SampleEntity.class, index);

29. Using Scroll For Big Result Set

Elasticsearch has a scroll API for getting big result set in chunks. ElasticsearchOperations has startScroll and continueScroll methods that can be used as below.

Example 79. Using startScroll and continueScroll
IndexCoordinates index = IndexCoordinates.of("sample-index");

SearchQuery searchQuery = new NativeSearchQueryBuilder()
  .withQuery(matchAllQuery())
  .withIndices(INDEX_NAME)
  .withTypes(TYPE_NAME)
  .withFields("message")
  .withPageable(PageRequest.of(0, 10))
  .build();

ScrolledPage<SampleEntity> scroll = operations.startScroll(1000, searchQuery, SampleEntity.class, index);

String scrollId = scroll.getScrollId();
List<SampleEntity> sampleEntities = new ArrayList<>();
while (scroll.hasContent()) {
  sampleEntities.addAll(scroll.getContent());
  scrollId = scroll.getScrollId();
  scroll = operations.continueScroll(scrollId, 1000, SampleEntity.class);
}
operations.clearScroll(scrollId);

ElasticsearchOperations additionally has the stream method which wraps the scan and scroll operations into a CloseableIterator.

Example 80. Using stream
IndexCoordinates index = IndexCoordinates.of("sample-index");

SearchQuery searchQuery = new NativeSearchQueryBuilder()
  .withQuery(matchAllQuery())
  .withIndices(INDEX_NAME)
  .withTypes(TYPE_NAME)
  .withFields("message")
  .withPageable(PageRequest.of(0, 10))
  .build();

CloseableIterator<SampleEntity> stream = elasticsearchTemplate.stream(searchQuery, SampleEntity.class, index);

List<SampleEntity> sampleEntities = new ArrayList<>();
while (stream.hasNext()) {
  sampleEntities.add(stream.next());
}
Appendix

Appendix A: Namespace reference

The <repositories /> Element

The <repositories /> element triggers the setup of the Spring Data repository infrastructure. The most important attribute is base-package, which defines the package to scan for Spring Data repository interfaces. See “XML configuration”. The following table describes the attributes of the <repositories /> element:

Table 3. Attributes
Name Description

base-package

Defines the package to be scanned for repository interfaces that extend *Repository (the actual interface is determined by the specific Spring Data module) in auto-detection mode. All packages below the configured package are scanned, too. Wildcards are allowed.

repository-impl-postfix

Defines the postfix to autodetect custom repository implementations. Classes whose names end with the configured postfix are considered as candidates. Defaults to Impl.

query-lookup-strategy

Determines the strategy to be used to create finder queries. See “Query Lookup Strategies” for details. Defaults to create-if-not-found.

named-queries-location

Defines the location to search for a Properties file containing externally defined queries.

consider-nested-repositories

Whether nested repository interface definitions should be considered. Defaults to false.

Appendix B: Populators namespace reference

The <populator /> element

The <populator /> element allows to populate the a data store via the Spring Data repository infrastructure.[4]

Table 4. Attributes
Name Description

locations

Where to find the files to read the objects from the repository shall be populated with.

Appendix C: Repository query keywords

Supported query keywords

The following table lists the keywords generally supported by the Spring Data repository query derivation mechanism. However, consult the store-specific documentation for the exact list of supported keywords, because some keywords listed here might not be supported in a particular store.

Table 5. Query keywords
Logical keyword Keyword expressions

AND

And

OR

Or

AFTER

After, IsAfter

BEFORE

Before, IsBefore

CONTAINING

Containing, IsContaining, Contains

BETWEEN

Between, IsBetween

ENDING_WITH

EndingWith, IsEndingWith, EndsWith

EXISTS

Exists

FALSE

False, IsFalse

GREATER_THAN

GreaterThan, IsGreaterThan

GREATER_THAN_EQUALS

GreaterThanEqual, IsGreaterThanEqual

IN

In, IsIn

IS

Is, Equals, (or no keyword)

IS_EMPTY

IsEmpty, Empty

IS_NOT_EMPTY

IsNotEmpty, NotEmpty

IS_NOT_NULL

NotNull, IsNotNull

IS_NULL

Null, IsNull

LESS_THAN

LessThan, IsLessThan

LESS_THAN_EQUAL

LessThanEqual, IsLessThanEqual

LIKE

Like, IsLike

NEAR

Near, IsNear

NOT

Not, IsNot

NOT_IN

NotIn, IsNotIn

NOT_LIKE

NotLike, IsNotLike

REGEX

Regex, MatchesRegex, Matches

STARTING_WITH

StartingWith, IsStartingWith, StartsWith

TRUE

True, IsTrue

WITHIN

Within, IsWithin

Appendix D: Repository query return types

Supported Query Return Types

The following table lists the return types generally supported by Spring Data repositories. However, consult the store-specific documentation for the exact list of supported return types, because some types listed here might not be supported in a particular store.

Geospatial types (such as GeoResult, GeoResults, and GeoPage) are available only for data stores that support geospatial queries.
Table 6. Query return types
Return type Description

void

Denotes no return value.

Primitives

Java primitives.

Wrapper types

Java wrapper types.

T

A unique entity. Expects the query method to return one result at most. If no result is found, null is returned. More than one result triggers an IncorrectResultSizeDataAccessException.

Iterator<T>

An Iterator.

Collection<T>

A Collection.

List<T>

A List.

Optional<T>

A Java 8 or Guava Optional. Expects the query method to return one result at most. If no result is found, Optional.empty() or Optional.absent() is returned. More than one result triggers an IncorrectResultSizeDataAccessException.

Option<T>

Either a Scala or Vavr Option type. Semantically the same behavior as Java 8’s Optional, described earlier.

Stream<T>

A Java 8 Stream.

Streamable<T>

A convenience extension of Iterable that directy exposes methods to stream, map and filter results, concatenate them etc.

Types that implement Streamable and take a Streamable constructor or factory method argument

Types that expose a constructor or ….of(…)/….valueOf(…) factory method taking a Streamable as argument. See Returning Custom Streamable Wrapper Types for details.

Vavr Seq, List, Map, Set

Vavr collection types. See Support for Vavr Collections for details.

Future<T>

A Future. Expects a method to be annotated with @Async and requires Spring’s asynchronous method execution capability to be enabled.

CompletableFuture<T>

A Java 8 CompletableFuture. Expects a method to be annotated with @Async and requires Spring’s asynchronous method execution capability to be enabled.

ListenableFuture

A org.springframework.util.concurrent.ListenableFuture. Expects a method to be annotated with @Async and requires Spring’s asynchronous method execution capability to be enabled.

Slice

A sized chunk of data with an indication of whether there is more data available. Requires a Pageable method parameter.

Page<T>

A Slice with additional information, such as the total number of results. Requires a Pageable method parameter.

GeoResult<T>

A result entry with additional information, such as the distance to a reference location.

GeoResults<T>

A list of GeoResult<T> with additional information, such as the average distance to a reference location.

GeoPage<T>

A Page with GeoResult<T>, such as the average distance to a reference location.

Mono<T>

A Project Reactor Mono emitting zero or one element using reactive repositories. Expects the query method to return one result at most. If no result is found, Mono.empty() is returned. More than one result triggers an IncorrectResultSizeDataAccessException.

Flux<T>

A Project Reactor Flux emitting zero, one, or many elements using reactive repositories. Queries returning Flux can emit also an infinite number of elements.

Single<T>

A RxJava Single emitting a single element using reactive repositories. Expects the query method to return one result at most. If no result is found, Mono.empty() is returned. More than one result triggers an IncorrectResultSizeDataAccessException.

Maybe<T>

A RxJava Maybe emitting zero or one element using reactive repositories. Expects the query method to return one result at most. If no result is found, Mono.empty() is returned. More than one result triggers an IncorrectResultSizeDataAccessException.

Flowable<T>

A RxJava Flowable emitting zero, one, or many elements using reactive repositories. Queries returning Flowable can emit also an infinite number of elements.
1. Currently in development
2. Out of maintenance
3. not yet implemented for the reactive client
4. see XML configuration