Setting and getting properties is done using the setPropertyValue(s) and getPropertyValue(s) methods that both come with a couple of overloaded variants. They’re all described in more detail in the javadocs Spring comes with. What’s important to know is that there are a couple of conventions for indicating properties of an object. A couple of examples:

Below you’ll find some examples of working with the BeanWrapper to get and set properties.

(This next section is not vitally important to you if you’re not planning to work with the BeanWrapper directly. If you’re just using the DataBinder and the BeanFactory and their out-of-the-box implementation, you should skip ahead to the section about PropertyEditors.)

Consider the following two classes:

public class Company {

    private String name;
    private Employee managingDirector;

    public String getName() {
        return this.name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Employee getManagingDirector() {
        return this.managingDirector;
    }

    public void setManagingDirector(Employee managingDirector) {
        this.managingDirector = managingDirector;
    }
}

public class Employee {

    private String name;

    private float salary;

    public String getName() {
        return this.name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public float getSalary() {
        return salary;
    }

    public void setSalary(float salary) {
        this.salary = salary;
    }
}

The following code snippets show some examples of how to retrieve and manipulate some of the properties of instantiated Companies and Employees:

BeanWrapper company = new BeanWrapperImpl(new Company());
// setting the company name..
company.setPropertyValue("name", "Some Company Inc.");
// ... can also be done like this:
PropertyValue value = new PropertyValue("name", "Some Company Inc.");
company.setPropertyValue(value);

// ok, let's create the director and tie it to the company:
BeanWrapper jim = new BeanWrapperImpl(new Employee());
jim.setPropertyValue("name", "Jim Stravinsky");
company.setPropertyValue("managingDirector", jim.getWrappedInstance());

// retrieving the salary of the managingDirector through the company
Float salary = (Float) company.getPropertyValue("managingDirector.salary");

Spring uses the concept of PropertyEditors to effect the conversion between an Object and a String. If you think about it, it sometimes might be handy to be able to represent properties in a different way than the object itself. For example, a Date can be represented in a human readable way (as the String '2007-14-09'), while we’re still able to convert the human readable form back to the original date (or even better: convert any date entered in a human readable form, back to Date objects). This behavior can be achieved by registering custom editors, of type java.beans.PropertyEditor. Registering custom editors on a BeanWrapper or alternately in a specific IoC container as mentioned in the previous chapter, gives it the knowledge of how to convert properties to the desired type. Read more about PropertyEditors in the javadocs of the java.beans package provided by Oracle.

A couple of examples where property editing is used in Spring:

Spring has a number of built-in PropertyEditors to make life easy. Each of those is listed below and they are all located in the org.springframework.beans.propertyeditors package. Most, but not all (as indicated below), are registered by default by BeanWrapperImpl. Where the property editor is configurable in some fashion, you can of course still register your own variant to override the default one:

Spring uses the java.beans.PropertyEditorManager to set the search path for property editors that might be needed. The search path also includes sun.bean.editors, which includes PropertyEditor implementations for types such as Font, Color, and most of the primitive types. Note also that the standard JavaBeans infrastructure will automatically discover PropertyEditor classes (without you having to register them explicitly) if they are in the same package as the class they handle, and have the same name as that class, with 'Editor' appended; for example, one could have the following class and package structure, which would be sufficient for the FooEditor class to be recognized and used as the PropertyEditor for Foo-typed properties.

com
  chank
    pop
      Foo
      FooEditor // the PropertyEditor for the Foo class

Note that you can also use the standard BeanInfo JavaBeans mechanism here as well (described in not-amazing-detail here). Find below an example of using the BeanInfo mechanism for explicitly registering one or more PropertyEditor instances with the properties of an associated class.

com
  chank
    pop
      Foo
      FooBeanInfo // the BeanInfo for the Foo class

Here is the Java source code for the referenced FooBeanInfo class. This would associate a CustomNumberEditor with the age property of the Foo class.

public class FooBeanInfo extends SimpleBeanInfo {

    public PropertyDescriptor[] getPropertyDescriptors() {
        try {
            final PropertyEditor numberPE = new CustomNumberEditor(Integer.class, true);
            PropertyDescriptor ageDescriptor = new PropertyDescriptor("age", Foo.class) {
                public PropertyEditor createPropertyEditor(Object bean) {
                    return numberPE;
                };
            };
            return new PropertyDescriptor[] { ageDescriptor };
        }
        catch (IntrospectionException ex) {
            throw new Error(ex.toString());
        }
    }
}

package example;

public class ExoticType {

    private String name;

    public ExoticType(String name) {
        this.name = name;
    }
}

public class DependsOnExoticType {

    private ExoticType type;

    public void setType(ExoticType type) {
        this.type = type;
    }
}

<bean id="sample" class="example.DependsOnExoticType">
    <property name="type" value="aNameForExoticType"/>
</bean>

// converts string representation to ExoticType object
package example;

public class ExoticTypeEditor extends PropertyEditorSupport {

    public void setAsText(String text) {
        setValue(new ExoticType(text.toUpperCase()));
    }
}

<bean class="org.springframework.beans.factory.config.CustomEditorConfigurer">
    <property name="customEditors">
        <map>
            <entry key="example.ExoticType" value="example.ExoticTypeEditor"/>
        </map>
    </property>
</bean>

package com.foo.editors.spring;

public final class CustomPropertyEditorRegistrar implements PropertyEditorRegistrar {

    public void registerCustomEditors(PropertyEditorRegistry registry) {

        // it is expected that new PropertyEditor instances are created
        registry.registerCustomEditor(ExoticType.class, new ExoticTypeEditor());

        // you could register as many custom property editors as are required here...
    }
}

<bean class="org.springframework.beans.factory.config.CustomEditorConfigurer">
    <property name="propertyEditorRegistrars">
        <list>
            <ref bean="customPropertyEditorRegistrar"/>
        </list>
    </property>
</bean>

<bean id="customPropertyEditorRegistrar"
    class="com.foo.editors.spring.CustomPropertyEditorRegistrar"/>

public final class RegisterUserController extends SimpleFormController {

    private final PropertyEditorRegistrar customPropertyEditorRegistrar;

    public RegisterUserController(PropertyEditorRegistrar propertyEditorRegistrar) {
        this.customPropertyEditorRegistrar = propertyEditorRegistrar;
    }

    protected void initBinder(HttpServletRequest request,
            ServletRequestDataBinder binder) throws Exception {
        this.customPropertyEditorRegistrar.registerCustomEditors(binder);
    }

    // other methods to do with registering a User
}

The SPI to implement type conversion logic is simple and strongly typed:

package org.springframework.core.convert.converter;

public interface Converter<S, T> {

    T convert(S source);

}

To create your own converter, simply implement the interface above. Parameterize S as the type you are converting from, and T as the type you are converting to. Such a converter can also be applied transparently if a collection or array of S needs to be converted to an array or collection of T, provided that a delegating array/collection converter has been registered as well (which DefaultConversionService does by default).

For each call to convert(S), the source argument is guaranteed to be NOT null. Your Converter may throw any unchecked exception if conversion fails; specifically, an IllegalArgumentException should be thrown to report an invalid source value. Take care to ensure that your Converter implementation is thread-safe.

Several converter implementations are provided in the core.convert.support package as a convenience. These include converters from Strings to Numbers and other common types. Consider StringToInteger as an example for a typical Converter implementation:

package org.springframework.core.convert.support;

final class StringToInteger implements Converter<String, Integer> {

    public Integer convert(String source) {
        return Integer.valueOf(source);
    }

}

When you need to centralize the conversion logic for an entire class hierarchy, for example, when converting from String to java.lang.Enum objects, implement ConverterFactory:

package org.springframework.core.convert.converter;

public interface ConverterFactory<S, R> {

    <T extends R> Converter<S, T> getConverter(Class<T> targetType);

}

Parameterize S to be the type you are converting from and R to be the base type defining the range of classes you can convert to. Then implement getConverter(Class<T>), where T is a subclass of R.

Consider the StringToEnum ConverterFactory as an example:

package org.springframework.core.convert.support;

final class StringToEnumConverterFactory implements ConverterFactory<String, Enum> {

    public <T extends Enum> Converter<String, T> getConverter(Class<T> targetType) {
        return new StringToEnumConverter(targetType);
    }

    private final class StringToEnumConverter<T extends Enum> implements Converter<String, T> {

        private Class<T> enumType;

        public StringToEnumConverter(Class<T> enumType) {
            this.enumType = enumType;
        }

        public T convert(String source) {
            return (T) Enum.valueOf(this.enumType, source.trim());
        }
    }
}

When you require a sophisticated Converter implementation, consider the GenericConverter interface. With a more flexible but less strongly typed signature, a GenericConverter supports converting between multiple source and target types. In addition, a GenericConverter makes available source and target field context you can use when implementing your conversion logic. Such context allows a type conversion to be driven by a field annotation, or generic information declared on a field signature.

package org.springframework.core.convert.converter;

public interface GenericConverter {

    public Set<ConvertiblePair> getConvertibleTypes();

    Object convert(Object source, TypeDescriptor sourceType, TypeDescriptor targetType);

}

To implement a GenericConverter, have getConvertibleTypes() return the supported source→target type pairs. Then implement convert(Object, TypeDescriptor, TypeDescriptor) to implement your conversion logic. The source TypeDescriptor provides access to the source field holding the value being converted. The target TypeDescriptor provides access to the target field where the converted value will be set.

A good example of a GenericConverter is a converter that converts between a Java Array and a Collection. Such an ArrayToCollectionConverter introspects the field that declares the target Collection type to resolve the Collection’s element type. This allows each element in the source array to be converted to the Collection element type before the Collection is set on the target field.

	Note
	Because GenericConverter is a more complex SPI interface, only use it when you need it. Favor Converter or ConverterFactory for basic type conversion needs.

public interface ConditionalConverter {

    boolean matches(TypeDescriptor sourceType, TypeDescriptor targetType);

}

public interface ConditionalGenericConverter
    extends GenericConverter, ConditionalConverter {

}

The ConversionService defines a unified API for executing type conversion logic at runtime. Converters are often executed behind this facade interface:

package org.springframework.core.convert;

public interface ConversionService {

    boolean canConvert(Class<?> sourceType, Class<?> targetType);

    <T> T convert(Object source, Class<T> targetType);

    boolean canConvert(TypeDescriptor sourceType, TypeDescriptor targetType);

    Object convert(Object source, TypeDescriptor sourceType, TypeDescriptor targetType);

}

Most ConversionService implementations also implement ConverterRegistry, which provides an SPI for registering converters. Internally, a ConversionService implementation delegates to its registered converters to carry out type conversion logic.

A robust ConversionService implementation is provided in the core.convert.support package. GenericConversionService is the general-purpose implementation suitable for use in most environments. ConversionServiceFactory provides a convenient factory for creating common ConversionService configurations.

A ConversionService is a stateless object designed to be instantiated at application startup, then shared between multiple threads. In a Spring application, you typically configure a ConversionService instance per Spring container (or ApplicationContext). That ConversionService will be picked up by Spring and then used whenever a type conversion needs to be performed by the framework. You may also inject this ConversionService into any of your beans and invoke it directly.

	Note
	If no ConversionService is registered with Spring, the original PropertyEditor-based system is used.

To register a default ConversionService with Spring, add the following bean definition with id conversionService:

<bean id="conversionService"
    class="org.springframework.context.support.ConversionServiceFactoryBean"/>

A default ConversionService can convert between strings, numbers, enums, collections, maps, and other common types. To supplement or override the default converters with your own custom converter(s), set the converters property. Property values may implement either of the Converter, ConverterFactory, or GenericConverter interfaces.

<bean id="conversionService"
        class="org.springframework.context.support.ConversionServiceFactoryBean">
    <property name="converters">
        <set>
            <bean class="example.MyCustomConverter"/>
        </set>
    </property>
</bean>

It is also common to use a ConversionService within a Spring MVC application. See Section 22.16.3, “Conversion and Formatting” in the Spring MVC chapter.

In certain situations you may wish to apply formatting during conversion. See Section 9.6.3, “FormatterRegistry SPI” for details on using FormattingConversionServiceFactoryBean.

To work with a ConversionService instance programmatically, simply inject a reference to it like you would for any other bean:

@Service
public class MyService {

    @Autowired
    public MyService(ConversionService conversionService) {
        this.conversionService = conversionService;
    }

    public void doIt() {
        this.conversionService.convert(...)
    }
}

For most use cases, the convert method specifying the targetType can be used but it will not work with more complex types such as a collection of a parameterized element. If you want to convert a List of Integer to a List of String programmatically, for instance, you need to provide a formal definition of the source and target types.

Fortunately, TypeDescriptor provides various options to make that straightforward:

DefaultConversionService cs = new DefaultConversionService();

List<Integer> input = ....
cs.convert(input,
    TypeDescriptor.forObject(input), // List<Integer> type descriptor
    TypeDescriptor.collection(List.class, TypeDescriptor.valueOf(String.class)));

Note that DefaultConversionService registers converters automatically which are appropriate for most environments. This includes collection converters, scalar converters, and also basic Object to String converters. The same converters can be registered with any ConverterRegistry using the static addDefaultConverters method on the DefaultConversionService class.

Converters for value types will be reused for arrays and collections, so there is no need to create a specific converter to convert from a Collection of S to a Collection of T, assuming that standard collection handling is appropriate.

The Formatter SPI to implement field formatting logic is simple and strongly typed:

package org.springframework.format;

public interface Formatter<T> extends Printer<T>, Parser<T> {
}

Where Formatter extends from the Printer and Parser building-block interfaces:

public interface Printer<T> {
    String print(T fieldValue, Locale locale);
}

import java.text.ParseException;

public interface Parser<T> {
    T parse(String clientValue, Locale locale) throws ParseException;
}

To create your own Formatter, simply implement the Formatter interface above. Parameterize T to be the type of object you wish to format, for example, java.util.Date. Implement the print() operation to print an instance of T for display in the client locale. Implement the parse() operation to parse an instance of T from the formatted representation returned from the client locale. Your Formatter should throw a ParseException or IllegalArgumentException if a parse attempt fails. Take care to ensure your Formatter implementation is thread-safe.

Several Formatter implementations are provided in format subpackages as a convenience. The number package provides a NumberFormatter, CurrencyFormatter, and PercentFormatter to format java.lang.Number objects using a java.text.NumberFormat. The datetime package provides a DateFormatter to format java.util.Date objects with a java.text.DateFormat. The datetime.joda package provides comprehensive datetime formatting support based on the Joda Time library.

Consider DateFormatter as an example Formatter implementation:

package org.springframework.format.datetime;

public final class DateFormatter implements Formatter<Date> {

    private String pattern;

    public DateFormatter(String pattern) {
        this.pattern = pattern;
    }

    public String print(Date date, Locale locale) {
        if (date == null) {
            return "";
        }
        return getDateFormat(locale).format(date);
    }

    public Date parse(String formatted, Locale locale) throws ParseException {
        if (formatted.length() == 0) {
            return null;
        }
        return getDateFormat(locale).parse(formatted);
    }

    protected DateFormat getDateFormat(Locale locale) {
        DateFormat dateFormat = new SimpleDateFormat(this.pattern, locale);
        dateFormat.setLenient(false);
        return dateFormat;
    }

}

The Spring team welcomes community-driven Formatter contributions; see jira.spring.io to contribute.

As you will see, field formatting can be configured by field type or annotation. To bind an Annotation to a formatter, implement AnnotationFormatterFactory:

package org.springframework.format;

public interface AnnotationFormatterFactory<A extends Annotation> {

    Set<Class<?>> getFieldTypes();

    Printer<?> getPrinter(A annotation, Class<?> fieldType);

    Parser<?> getParser(A annotation, Class<?> fieldType);

}

Parameterize A to be the field annotationType you wish to associate formatting logic with, for example org.springframework.format.annotation.DateTimeFormat. Have getFieldTypes() return the types of fields the annotation may be used on. Have getPrinter() return a Printer to print the value of an annotated field. Have getParser() return a Parser to parse a clientValue for an annotated field.

The example AnnotationFormatterFactory implementation below binds the @NumberFormat Annotation to a formatter. This annotation allows either a number style or pattern to be specified:

public final class NumberFormatAnnotationFormatterFactory
        implements AnnotationFormatterFactory<NumberFormat> {

    public Set<Class<?>> getFieldTypes() {
        return new HashSet<Class<?>>(asList(new Class<?>[] {
            Short.class, Integer.class, Long.class, Float.class,
            Double.class, BigDecimal.class, BigInteger.class }));
    }

    public Printer<Number> getPrinter(NumberFormat annotation, Class<?> fieldType) {
        return configureFormatterFrom(annotation, fieldType);
    }

    public Parser<Number> getParser(NumberFormat annotation, Class<?> fieldType) {
        return configureFormatterFrom(annotation, fieldType);
    }

    private Formatter<Number> configureFormatterFrom(NumberFormat annotation,
            Class<?> fieldType) {
        if (!annotation.pattern().isEmpty()) {
            return new NumberFormatter(annotation.pattern());
        } else {
            Style style = annotation.style();
            if (style == Style.PERCENT) {
                return new PercentFormatter();
            } else if (style == Style.CURRENCY) {
                return new CurrencyFormatter();
            } else {
                return new NumberFormatter();
            }
        }
    }
}

To trigger formatting, simply annotate fields with @NumberFormat:

public class MyModel {

    @NumberFormat(style=Style.CURRENCY)
    private BigDecimal decimal;

}

public class MyModel {

    @DateTimeFormat(iso=ISO.DATE)
    private Date date;

}

The FormatterRegistry is an SPI for registering formatters and converters. FormattingConversionService is an implementation of FormatterRegistry suitable for most environments. This implementation may be configured programmatically or declaratively as a Spring bean using FormattingConversionServiceFactoryBean. Because this implementation also implements ConversionService, it can be directly configured for use with Spring’s DataBinder and the Spring Expression Language (SpEL).

Review the FormatterRegistry SPI below:

package org.springframework.format;

public interface FormatterRegistry extends ConverterRegistry {

    void addFormatterForFieldType(Class<?> fieldType, Printer<?> printer, Parser<?> parser);

    void addFormatterForFieldType(Class<?> fieldType, Formatter<?> formatter);

    void addFormatterForFieldType(Formatter<?> formatter);

    void addFormatterForAnnotation(AnnotationFormatterFactory<?, ?> factory);

}

As shown above, Formatters can be registered by fieldType or annotation.

The FormatterRegistry SPI allows you to configure Formatting rules centrally, instead of duplicating such configuration across your Controllers. For example, you might want to enforce that all Date fields are formatted a certain way, or fields with a specific annotation are formatted in a certain way. With a shared FormatterRegistry, you define these rules once and they are applied whenever formatting is needed.

The FormatterRegistrar is an SPI for registering formatters and converters through the FormatterRegistry:

package org.springframework.format;

public interface FormatterRegistrar {

    void registerFormatters(FormatterRegistry registry);

}

A FormatterRegistrar is useful when registering multiple related converters and formatters for a given formatting category, such as Date formatting. It can also be useful where declarative registration is insufficient. For example when a formatter needs to be indexed under a specific field type different from its own <T> or when registering a Printer/Parser pair. The next section provides more information on converter and formatter registration.

See Section 22.16.3, “Conversion and Formatting” in the Spring MVC chapter.

JSR-303 standardizes validation constraint declaration and metadata for the Java platform. Using this API, you annotate domain model properties with declarative validation constraints and the runtime enforces them. There are a number of built-in constraints you can take advantage of. You may also define your own custom constraints.

To illustrate, consider a simple PersonForm model with two properties:

public class PersonForm {
    private String name;
    private int age;
}

JSR-303 allows you to define declarative validation constraints against such properties:

public class PersonForm {

    @NotNull
    @Size(max=64)
    private String name;

    @Min(0)
    private int age;

}

When an instance of this class is validated by a JSR-303 Validator, these constraints will be enforced.

For general information on JSR-303/JSR-349, see the Bean Validation website. For information on the specific capabilities of the default reference implementation, see the Hibernate Validator documentation. To learn how to setup a Bean Validation provider as a Spring bean, keep reading.

Spring provides full support for the Bean Validation API. This includes convenient support for bootstrapping a JSR-303/JSR-349 Bean Validation provider as a Spring bean. This allows for a javax.validation.ValidatorFactory or javax.validation.Validator to be injected wherever validation is needed in your application.

Use the LocalValidatorFactoryBean to configure a default Validator as a Spring bean:

<bean id="validator"
    class="org.springframework.validation.beanvalidation.LocalValidatorFactoryBean"/>

The basic configuration above will trigger Bean Validation to initialize using its default bootstrap mechanism. A JSR-303/JSR-349 provider, such as Hibernate Validator, is expected to be present in the classpath and will be detected automatically.

import javax.validation.Validator;

@Service
public class MyService {

    @Autowired
    private Validator validator;

import org.springframework.validation.Validator;

@Service
public class MyService {

    @Autowired
    private Validator validator;

}

@Target({ElementType.METHOD, ElementType.FIELD})
@Retention(RetentionPolicy.RUNTIME)
@Constraint(validatedBy=MyConstraintValidator.class)
public @interface MyConstraint {
}

import javax.validation.ConstraintValidator;

public class MyConstraintValidator implements ConstraintValidator {

    @Autowired;
    private Foo aDependency;

    ...
}

<bean class="org.springframework.validation.beanvalidation.MethodValidationPostProcessor"/>

Since Spring 3, a DataBinder instance can be configured with a Validator. Once configured, the Validator may be invoked by calling binder.validate(). Any validation Errors are automatically added to the binder’s BindingResult.

When working with the DataBinder programmatically, this can be used to invoke validation logic after binding to a target object:

Foo target = new Foo();
DataBinder binder = new DataBinder(target);
binder.setValidator(new FooValidator());

// bind to the target object
binder.bind(propertyValues);

// validate the target object
binder.validate();

// get BindingResult that includes any validation errors
BindingResult results = binder.getBindingResult();

A DataBinder can also be configured with multiple Validator instances via dataBinder.addValidators and dataBinder.replaceValidators. This is useful when combining globally configured Bean Validation with a Spring Validator configured locally on a DataBinder instance. See ???.

See Section 22.16.4, “Validation” in the Spring MVC chapter.