2. RestTemplate Module

2.1 Introduction

Spring's RestTemplate is a robust, popular Java-based REST client. The Spring for Android RestTemplate Module provides a version of RestTemplate that works in an Android environment.

2.2 Overview

The RestTemplate class is the heart of the Spring for Android RestTemplate library. It is conceptually similar to other template classes found in other Spring portfolio projects. RestTemplate's behavior is customized by providing callback methods and configuring the HttpMessageConverter used to marshal objects into the HTTP request body and to unmarshal any response back into an object. When you create a new RestTemplate instance, the constructor sets up several supporting objects that make up the RestTemplate functionality.

Here is an overview of the functionality supported within RestTemplate.

2.2.1 HTTP Client

RestTemplate provides an abstraction for making RESTful HTTP requests, and internally, RestTemplate utilizes a native Android HTTP client library for those requests. There are two native HTTP clients available on Android, the standard J2SE facilities, and the HttpComponents HttpClient. The standard JS2SE facilities are made available through the SimpleClientHttpRequestFactory, while the HttpClient is made available through the HttpComponentsClientHttpRequestFactory. The default ClientHttpRequestFactory used when you create a new RestTemplate instance differs based on the version of Android on which your application is running.

Google recommends to use the J2SE facilities on Gingerbread (Version 2.3) and newer, while previous versions should use the HttpComponents HttpClient. Based on this recommendation RestTemplate checks the version of Android on which your app is running and uses the appropriate ClientHttpRequestFactory. To utilize a specific ClientHttpRequestFactory you must either pass a new instance into the RestTemplate constructor, or call setRequestFactory(ClientHttpRequestFactory requestFactory) on an existing RestTemplate instance.

2.2.2 Gzip Compression

RestTemplate supports sending and receiving data encoded with gzip compression. The HTTP specification allows for additional values in the Accept-Encoding header field, however RestTemplate only supports gzip compression at this time.

2.2.3 Object to JSON Marshaling

Object to JSON marshaling in Spring for Android RestTemplate requires the use of a third party JSON mapping library. There are three libraries supported in Spring for Android, Jackson JSON Processor, Jackson 2.x, and Google Gson. While Jackson is a well known JSON parsing library, the Gson library is smaller, which would result in an smaller Android app when packaged.

2.2.4 Object to XML Marshaling

Object to XML marshaling in Spring for Android RestTemplate requires the use of a third party XML mapping library. The Simple XML serializer is used to provide this marshaling functionality.

2.2.5 RSS and Atom Support

RSS and Atom feed support in Spring for Android RestTemplate requires the use of a third party feed reader library. The Android ROME Feed Reader is used to provide this functionality.

2.3 How to get

There are a few methods for including external jars in your Android app. One is to manually download them and include them in your app's libs/ folder. Another option is to use Maven for dependency management.

2.3.1 Standard Installation

In order to use RestTemplate in your Android application, you must include the following Spring for Android jars in the libs/ folder. These are available from the SpringSource Community Downloads page.

  • spring-android-rest-template-{version}.jar
  • spring-android-core-{version}.jar

If you are building your project with Ant, Ant will automatically include any jars located in the libs/ folder located in the root of your project. However, in Eclipse you must manually add the jars to the Build Path. Follow these steps to add the jars to your existing Android project in Eclipse.

  1. Refresh the project in Eclipse so the libs/ folder and jars display in the Package Explorer.
  2. Right-Click (Command-Click) the first jar.
  3. Select the BuildPath submenu.
  4. Select Add to Build Path from the context menu.
  5. Repeat these steps for each jar.

2.3.2 Maven Dependencies

Google's provided Android toolset does not include dependency management support. However, through the use of third party tools, you can use Maven to manage dependencies and build your Android app. See the Spring for Android and Maven section for more information. Additional dependencies may be required, depending on which HTTP Message Converters you are using within RestTemplate. See the Message Converters section for more information.

Add the spring-android-rest-template artifact to your classpath:

<dependency>
    <groupId>org.springframework.android</groupId>
    <artifactId>spring-android-rest-template</artifactId>
    <version>${spring-android-version}</version>
</dependency>
			

The transitive dependencies are automatically imported by Maven, but they are listed here for clarity.

<dependency>
    <groupId>org.springframework.android</groupId>
    <artifactId>spring-android-core</artifactId>
    <version>${spring-android-version}</version>
</dependency>
			

2.4 RestTemplate Constructors

The four RestTemplate constructors are listed below. The default constructor does not include any message body converters. You must add a message converter when using the default constructor. If you would like to include a default set of message converters with a new RestTemplate instance, then you can pass true for the includeDefaultConverters parameter. For a list of default converters, see the HTTP Message Conversion section. Additionally, if you would like to specify a different ClientHttpRequestFactory then you can do so by passing it in to the requestFactory parameter.

RestTemplate();

RestTemplate(boolean includeDefaultConverters);

RestTemplate(ClientHttpRequestFactory requestFactory);

RestTemplate(boolean includeDefaultConverters, ClientHttpRequestFactory requestFactory);
		

2.5 RestTemplate Methods

RestTemplate provides higher level methods that correspond to each of the six main HTTP methods. These methods make it easy to invoke many RESTful services and enforce REST best practices.

The names of RestTemplate methods follow a naming convention, the first part indicates what HTTP method is being invoked and the second part indicates what is returned. For example, the method getForObject() will perform a GET, convert the HTTP response into an object type of your choice and return that object. The method postForLocation() will do a POST, converting the given object into a HTTP request and return the response HTTP Location header where the newly created object can be found. In case of an exception processing the HTTP request, an exception of the type RestClientException will be thrown. This behavior can be changed by plugging in another ResponseErrorHandler implementation into the RestTemplate.

For more information on RestTemplate and it's associated methods, please refer to the API Javadoc

2.5.1 HTTP DELETE

public void delete(String url, Object... urlVariables) throws RestClientException;

public void delete(String url, Map<String, ?> urlVariables) throws RestClientException;

public void delete(URI url) throws RestClientException;
		

2.5.2 HTTP GET

public <T> T getForObject(String url, Class<T> responseType, Object... urlVariables) throws RestClientException;

public <T> T getForObject(String url, Class<T> responseType, Map<String, ?> urlVariables) throws RestClientException;

public <T> T getForObject(URI url, Class<T> responseType) throws RestClientException;

public <T> ResponseEntity<T> getForEntity(String url, Class<T> responseType, Object... urlVariables);

public <T> ResponseEntity<T> getForEntity(String url, Class<T> responseType, Map<String, ?> urlVariables);

public <T> ResponseEntity<T> getForEntity(URI url, Class<T> responseType) throws RestClientException;
		

2.5.3 HTTP HEAD

public HttpHeaders headForHeaders(String url, Object... urlVariables) throws RestClientException;

public HttpHeaders headForHeaders(String url, Map<String, ?> urlVariables) throws RestClientException;

public HttpHeaders headForHeaders(URI url) throws RestClientException;
		

2.5.4 HTTP OPTIONS

public Set<HttpMethod> optionsForAllow(String url, Object... urlVariables) throws RestClientException;

public Set<HttpMethod> optionsForAllow(String url, Map<String, ?> urlVariables) throws RestClientException;

public Set<HttpMethod> optionsForAllow(URI url) throws RestClientException;
		

2.5.5 HTTP POST

public URI postForLocation(String url, Object request, Object... urlVariables) throws RestClientException;

public URI postForLocation(String url, Object request, Map<String, ?> urlVariables);

public URI postForLocation(URI url, Object request) throws RestClientException;

public <T> T postForObject(String url, Object request, Class<T> responseType, Object... uriVariables);

public <T> T postForObject(String url, Object request, Class<T> responseType, Map<String, ?> uriVariables);

public <T> T postForObject(URI url, Object request, Class<T> responseType) throws RestClientException;

public <T> ResponseEntity<T> postForEntity(String url, Object request, Class<T> responseType, Object... uriVariables);

public <T> ResponseEntity<T> postForEntity(String url, Object request, Class<T> responseType, Map<String, ?> uriVariables) throws RestClientException;

public <T> ResponseEntity<T> postForEntity(URI url, Object request, Class<T> responseType) throws RestClientException;
		

2.5.6 HTTP PUT

public void put(String url, Object request, Object... urlVariables) throws RestClientException;

public void put(String url, Object request, Map<String, ?> urlVariables) throws RestClientException;

public void put(String url, Object request, Map<String, ?> urlVariables) throws RestClientException;
		

2.6 HTTP Message Conversion

Objects passed to and returned from the methods getForObject(), getForEntity(), postForLocation(), postForObject() and put() are converted to HTTP requests and from HTTP responses by HttpMessageConverter instances. The HttpMessageConverter interface is shown below to give you a better feel for its functionality.

public interface HttpMessageConverter<T> {

    // Indicates whether the given class can be read by this converter.
    boolean canRead(Class<?> clazz, MediaType mediaType);

    // Indicates whether the given class can be written by this converter.
    boolean canWrite(Class<?> clazz, MediaType mediaType);

    // Return the list of [email protected] MediaType} objects supported by this converter.
    List<MediaType> getSupportedMediaTypes();

    // Read an object of the given type form the given input message, and returns it.
    T read(Class<? extends T> clazz, HttpInputMessage inputMessage)
            throws IOException, HttpMessageNotReadableException;

    // Write an given object to the given output message.
    void write(T t, MediaType contentType, HttpOutputMessage outputMessage)
            throws IOException, HttpMessageNotWritableException;

}
	

Concrete implementations for the main media (mime) types are provided in the framework.

2.6.1 Default Message Converters

For performance reasons, the default RestTemplate constructor does not register any message converters. However, if you pass true to the alternate constructor, then converters for the main mime types are registered. You can also write your own converter and register it via the messageConverters property.

When using the alternate RestTemplate constructor, the default converter instances registered with the template are ByteArrayHttpMessageConverter, StringHttpMessageConverter, and ResourceHttpMessageConverter. If your app is running on Android 2.2 or later, then XmlAwareFormHttpMessageConverter and SourceHttpMessageConverter are registered, as these two message converters require javax.xml.transform.Source. On Android 2.1, this falls back to the FormHttpMessageConverter which lacks some of the XML support in the other two. See the following table for more information.

Table 2.1. Default Message Converters
Message Body ConverterInclusion Rule
ByteArrayHttpMessageConverterAlways included
StringHttpMessageConverter
ResourceHttpMessageConverter
SourceHttpMessageConverterIncluded on Android 2.2 (Froyo) or newer, where javax.xml.transform.Source is available.
XmlAwareFormHttpMessageConverter
FormHttpMessageConverterIncluded on Android 2.1 (Eclair) and older.
SimpleXmlHttpMessageConverterIncluded if the Simple XML serializer is present.
MappingJackson2HttpMessageConverterIncluded if the Jackson 2.x JSON processor is present.
MappingJacksonHttpMessageConverterIncluded if the Jackson 1.x JSON processor is present. Jackson 2.x support takes precedence over Jackson 1.x if both versions are available on the classpath.
SyndFeedHttpMessageConverterIncluded if the Android ROME Feed Reader is present.

2.6.2 Available Message Converters

The following HttpMessageConverter implementations are available in Spring for Android. For all converters a default media type is used but can be overridden through the supportedMediaTypes property.

ByteArrayHttpMessageConverter

An HttpMessageConverter implementation that can read and write byte arrays from the HTTP request and response. By default, this converter supports all media types (*/*), and writes with a Content-Type of application/octet-stream. This can be overridden by setting the supportedMediaTypes property, and overriding getContentType(byte[]).

FormHttpMessageConverter

An HttpMessageConverter implementation that can read and write form data from the HTTP request and response. By default, this converter reads and writes the media type application/x-www-form-urlencoded. Form data is read from and written into a MultiValueMap<String, String>.

XmlAwareFormHttpMessageConverter

Extension of FormHttpMessageConverter, adding support for XML-based parts through a SourceHttpMessageConverter

ResourceHttpMessageConverter

An HttpMessageConverter implementation that can read and write Resource Resources. By default, this converter can read all media types. application/octet-stream is used to determine the Content-Type of written resources

SourceHttpMessageConverter

An HttpMessageConverter implementation that can read and write javax.xml.transform.Source from the HTTP request and response. Only DOMSource, SAXSource, and StreamSource are supported. By default, this converter supports text/xml and application/xml.

StringHttpMessageConverter

An HttpMessageConverter implementation that can read and write Strings from the HTTP request and response. By default, this converter supports all text media types (text/*), and writes with a Content-Type of text/plain.

SimpleXmlHttpMessageConverter

An HttpMessageConverter implementation that can read and write XML from the HTTP request and response using Simple Framework's Serializer. XML mapping can be customized as needed through the use of Simple's provided annotations. When additional control is needed, a custom Serializer can be injected through the Serializer property. By default, this converter reads and writes the media types application/xml, text/xml, and application/*+xml.

It is important to note that this is not a Spring OXM compatible message converter. It is a standalone implementation that enables XML serialization through Spring for Android.

Add the following dependency to your classpath to enable the SimpleXmlHttpMessageConverter.

<dependency>
    <groupId>org.simpleframework</groupId>
    <artifactId>simple-xml</artifactId>
    <version>${simple-version}</version>
</dependency>
			

MappingJackson2HttpMessageConverter

An HttpMessageConverter implementation that can read and write JSON using Jackson (2.x)'s ObjectMapper. JSON mapping can be customized as needed through the use of Jackson's provided annotations. When further control is needed, a custom ObjectMapper can be injected through the ObjectMapper property for cases where custom JSON serializers/deserializers need to be provided for specific types. By default this converter supports application/json.

Please note that this message converter and the GsonHttpMessageConverter both support application/json by default. Because of this, you should only add one JSON message converter to a RestTemplate instance. RestTemplate will use the first converter it finds that matches the specified mime type, so including both could produce unintended results.

Include the following dependencies in your classpath to enable the MappingJackson2HttpMessageConverter. Please note that if you are manually copying the jars into your project, you will also need to include the jackson-annotations and jackson-core jars.

<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-databind</artifactId>
    <version>${jackson-version}</version>
</dependency>
			

If you would prefer to use the Jackson JSON Processor instead, then include the following dependencies in your classpath to enable the MappingJacksonHttpMessageConverter. Please note that if you are manually copying the jars into your project, you will also need to include the jackson-core-asl jar.

<dependency>
    <groupId>org.codehaus.jackson</groupId>
    <artifactId>jackson-mapper-asl</artifactId>
    <version>${jackson-version}</version>
</dependency>
			

GsonHttpMessageConverter

An HttpMessageConverter implementation that can read and write JSON using Google Gson's Gson class. JSON mapping can be customized as needed through the use of Gson's provided annotations. When further control is needed, a custom Gson can be injected through the Gson property for cases where custom JSON serializers/deserializers need to be provided for specific types. By default this converter supports application/json.

Please note that this message converter and the MappingJackson2HttpMessageConverter both support application/json by default. Because of this, you should only add one JSON message converter to a RestTemplate instance. RestTemplate will use the first converter it finds that matches the specified mime type, so including both could produce unintended results.

Include the following dependency in your classpath to enable the GsonHttpMessageConverter.

<dependency>
    <groupId>com.google.code.gson</groupId>
    <artifactId>gson</artifactId>
    <version>${gson-version}</version>
</dependency>
			

SyndFeedHttpMessageConverter

An HttpMessageConverter implementation that can read and write RSS and Atom feeds from the HTTP request and response using Android ROME Feed Reader. The data is read from and written into a com.google.code.rome.android.repackaged.com.sun.syndication.feed.synd.SyndFeed. By default, this converter supports application/rss+xml and application/atom+xml.

Add the following dependencies to your classpath to enable the SyndFeedHttpMessageConverter, RssChannelHttpMessageConverter, or AtomFeedHttpMessageConverter. This library depends on a forked version of JDOM to work on Android 2.1 and earlier. The JDOM library addresses a bug in the Android XML parser.

<dependency>
    <groupId>com.google.code.android-rome-feed-reader</groupId>
    <artifactId>android-rome-feed-reader</artifactId>
    <version>${android-rome-version}</version>
</dependency>
			

<dependency>
    <groupId>org.jdom</groupId>
    <artifactId>jdom</artifactId>
    <version>${jdom-fork-version}</version>
</dependency>
			

The Android ROME Feed Reader is not available through Maven Central. When using Maven, you will need to include the following repository in your POM.

<!-- For developing with Android ROME Feed Reader -->
<repository>
    <id>android-rome-feed-reader-repository</id>
    <name>Android ROME Feed Reader Repository</name>
    <url>https://android-rome-feed-reader.googlecode.com/svn/maven2/releases</url>
</repository>
			

RssChannelHttpMessageConverter

An HttpMessageConverter implementation that can read and write RSS feeds from the HTTP request and response using Android ROME Feed Reader. The data is read from and written into a com.google.code.rome.android.repackaged.com.sun.syndication.feed.rss.Channel. By default, this converter supports application/rss+xml.

The SyndFeedHttpMessageConverter provides a higher level of abstraction around RSS and Atom feeds, the RssChannelHttpMessageConverter is not included in the default set of message converters when you create a new RestTemplate instance. If you prefer to use this message converter then you have to manually add it to the RestTemplate instance.

See the SyndFeedHttpMessageConverter section for information about the required Android ROME Feed Reader dependencies.

AtomFeedHttpMessageConverter

An HttpMessageConverter implementation that can read and write Atom feeds from the HTTP request and response using Android ROME Feed Reader. The data is read from and written into a com.google.code.rome.android.repackaged.com.sun.syndication.feed.atom.Feed. By default, this converter supports application/atom+xml.

Because the SyndFeedHttpMessageConverter provides a higher level of abstraction around RSS and Atom feeds, the AtomFeedHttpMessageConverter is not included in the default set of message converters when you create a new RestTemplate instance. If you prefer to use this message converter then you have to manually add it to the RestTemplate instance.

See the SyndFeedHttpMessageConverter section for information about the required Android ROME Feed Reader dependencies.

2.7 Usage Examples

Using RestTemplate, it's easy to invoke RESTful APIs. Below are several usage examples that illustrate the different methods for making RESTful requests.

All of the following examples are based on a sample Android application. You can retrieve the source code for the sample app with the following command:

$ git clone git://github.com/SpringSource/spring-android-samples.git
	

2.7.1 Basic Usage Example

The following example shows a query to google for the search term "SpringSource".

String url = "https://ajax.googleapis.com/ajax/services/search/web?v=1.0&q={query}";
			
// Create a new RestTemplate instance
RestTemplate restTemplate = new RestTemplate();

// Add the String message converter
restTemplate.getMessageConverters().add(new StringHttpMessageConverter());

// Make the HTTP GET request, marshaling the response to a String
String result = restTemplate.getForObject(url, String.class, "SpringSource");
		

2.7.2 Using Gzip Compression

Gzip compression can significantly reduce the size of the response data being returned in a REST request. Gzip must be supported by the web server to which the request is being made. By setting the content coding type of the Accept-Encoding header to gzip, you are requesting that the server respond using gzip compression. If gzip is available, or enabled on the server, then it should return a compressed response. RestTemplate checks the Content-Encoding header in the response to determine if, in fact, the response is gzip compressed. At this time, RestTemplate only supports the gzip content coding type in the Content-Encoding header. If the response data is determined to be gzip compressed, then a GZIPInputStream is used to decompress it.

The following example shows how to request a gzip compressed response from the server.

// Add the gzip Accept-Encoding header
HttpHeaders requestHeaders = new HttpHeaders();
requestHeaders.setAcceptEncoding(ContentCodingType.GZIP);
HttpEntity<?> requestEntity = new HttpEntity<Object>(requestHeaders);

// Create a new RestTemplate instance
RestTemplate restTemplate = new RestTemplate();

// Add the String message converter
restTemplate.getMessageConverters().add(new StringHttpMessageConverter());

// Make the HTTP GET request, marshaling the response to a String
ResponseEntity<String> response = restTemplate.exchange(url, HttpMethod.GET, requestEntity, String.class);
		

One thing to note, is that when using the J2SE facilities with the SimpleClientHttpRequestFactory, Gingerbread and newer automatically set the Accept-Encoding header to request gzip responses. This is built in functionality of newer versions of Android. If you desire to disable gzip, then you must set the identity value in the header.

// Add the identity Accept-Encoding header
HttpHeaders requestHeaders = new HttpHeaders();
requestHeaders.setAcceptEncoding(ContentCodingType.IDENTITY);
HttpEntity<?> requestEntity = new HttpEntity<Object>(requestHeaders);

// Create a new RestTemplate instance
RestTemplate restTemplate = new RestTemplate();

// Add the String message converter
restTemplate.getMessageConverters().add(new StringHttpMessageConverter());

// Make the HTTP GET request, marshaling the response to a String
ResponseEntity<String> response = restTemplate.exchange(url, HttpMethod.GET, requestEntity, String.class);
		

2.7.3 Retrieving JSON data via HTTP GET

Suppose you have defined a Java object you wish to populate from a RESTful web request that returns JSON content.

Define your object based on the JSON data being returned from the RESTful request:

public class Event {

    private Long id;

    private String title;
	
    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getTitle() {
        return title;
    }
	
    public String setTitle(String title) {
        this.title = title;
    }
}
		

Make the REST request:

// Create a new RestTemplate instance
RestTemplate restTemplate = new RestTemplate();

// Add the Jackson message converter
restTemplate.getMessageConverters().add(new MappingJackson2HttpMessageConverter());

// Make the HTTP GET request, marshaling the response from JSON to an array of Events
Event[] events = restTemplate.getForObject(url, Event[].class);
		

You can also set the Accept header for the request:

// Set the Accept header
HttpHeaders requestHeaders = new HttpHeaders();
requestHeaders.setAccept(Collections.singletonList(new MediaType("application","json")));
HttpEntity<?> requestEntity = new HttpEntity<Object>(requestHeaders);

// Create a new RestTemplate instance
RestTemplate restTemplate = new RestTemplate();

// Add the Jackson message converter
restTemplate.getMessageConverters().add(new MappingJackson2HttpMessageConverter());

// Make the HTTP GET request, marshaling the response from JSON to an array of Events
ResponseEntity<Event[]> responseEntity = restTemplate.exchange(url, HttpMethod.GET, requestEntity, Event[].class);
Event[] events = responseEntity.getBody();
		

Alternatively, you can use the GsonHttpMessageConverter for JSON marshaling. The following repeats the same request, utilizing Gson.

// Set the Accept header
HttpHeaders requestHeaders = new HttpHeaders();
requestHeaders.setAccept(Collections.singletonList(new MediaType("application","json")));
HttpEntity<?> requestEntity = new HttpEntity<Object>(requestHeaders);

// Create a new RestTemplate instance
RestTemplate restTemplate = new RestTemplate();

// Add the Gson message converter
restTemplate.getMessageConverters().add(new GsonHttpMessageConverter());

// Make the HTTP GET request, marshaling the response from JSON to an array of Events
ResponseEntity<Event[]> responseEntity = restTemplate.exchange(url, HttpMethod.GET, requestEntity, Event[].class);
Event[] events = responseEntity.getBody();
		

2.7.4 Retrieving XML data via HTTP GET

Using the same Java object we defined earlier, we can modify the requests to retrieve XML.

Define your object based on the XML data being returned from the RESTful request. Note the annotations used by Simple to marshal the object:

@Root
public class Event {

    @Element
    private Long id;

    @Element
    private String title;

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getTitle() {
        return title;
    }

    public String setTitle(String title) {
        this.title = title;
    }
}
		

To marshal an array of events from xml, we need to define a wrapper class for the list:

@Root(name="events")
public class EventList {

   @ElementList(inline=true)
   private List<Event> events;

   public List<Event> getEvents() {
      return events;
   }

   public void setEvents(List<Event> events) {
       this.events = events;
   }
}
		

Make the REST request:

// Create a new RestTemplate instance
RestTemplate restTemplate = new RestTemplate();

// Add the Simple XML message converter
restTemplate.getMessageConverters().add(new SimpleXmlHttpMessageConverter());

// Make the HTTP GET request, marshaling the response from XML to an EventList object
EventList eventList = restTemplate.getForObject(url, EventList.class);
		

You can also specify the Accept header for the request:

// Set the Accept header
HttpHeaders requestHeaders = new HttpHeaders();
requestHeaders.setAccept(Collections.singletonList(new MediaType("application","xml")));
HttpEntity<?> requestEntity = new HttpEntity<Object>(requestHeaders);

// Create a new RestTemplate instance
RestTemplate restTemplate = new RestTemplate();

// Add the Simple XML message converter
restTemplate.getMessageConverters().add(new SimpleXmlHttpMessageConverter());

// Make the HTTP GET request, marshaling the response from XML to an EventList
ResponseEntity<EventList> responseEntity = restTemplate.exchange(url, HttpMethod.GET, requestEntity, EventList.class);
EventList eventList = responseEntity.getBody();
		

2.7.5 Send JSON data via HTTP POST

POST a Java object you have defined to a RESTful service that accepts JSON data.

Define your object based on the JSON data expected by the RESTful request:

public class Message 
{
    private long id;

    private String subject;

    private String text;

    public void setId(long id) {
        this.id = id;
    }

    public long getId() {
        return id;
    }

    public void setSubject(String subject) {
        this.subject = subject;
    }

    public String getSubject() {
        return subject;
    }

    public void setText(String text) {
        this.text = text;
    }

    public String getText() {
        return text;
    }
}
		

Make the REST request. In this example, the request responds with a string value:

// Create and populate a simple object to be used in the request
Message message = new Message();
message.setId(555);
message.setSubject("test subject");
message.setText("test text");

// Create a new RestTemplate instance
RestTemplate restTemplate = new RestTemplate();

// Add the Jackson and String message converters
restTemplate.getMessageConverters().add(new MappingJackson2HttpMessageConverter());
restTemplate.getMessageConverters().add(new StringHttpMessageConverter());

// Make the HTTP POST request, marshaling the request to JSON, and the response to a String
String response = restTemplate.postForObject(url, message, String.class);
		

You can also specify the Content-Type header in your request:

// Create and populate a simple object to be used in the request
Message message = new Message();
message.setId(555);
message.setSubject("test subject");
message.setText("test text");

// Set the Content-Type header
HttpHeaders requestHeaders = new HttpHeaders();
requestHeaders.setContentType(new MediaType("application","json"));
HttpEntity<Message> requestEntity = new HttpEntity<Message>(message, requestHeaders);

// Create a new RestTemplate instance
RestTemplate restTemplate = new RestTemplate();

// Add the Jackson and String message converters
restTemplate.getMessageConverters().add(new MappingJackson2HttpMessageConverter());
restTemplate.getMessageConverters().add(new StringHttpMessageConverter());

// Make the HTTP POST request, marshaling the request to JSON, and the response to a String
ResponseEntity<String> responseEntity = restTemplate.exchange(url, HttpMethod.POST, requestEntity, String.class);
String result = responseEntity.getBody();
		

2.7.6 Retrieve RSS or Atom feed

The following is a basic example of loading an RSS feed:

// Create a new RestTemplate instance
RestTemplate restTemplate = new RestTemplate();

// Add the ROME message converter
restTemplate.getMessageConverters().add(new SyndFeedHttpMessageConverter());

// Make the HTTP GET request, marshaling the response to a SyndFeed object
SyndFeed = restTemplate.getForObject(url, SyndFeed.class);
		

It is possible that you need to adjust the Media Type associated with the SyndFeedHttpMessageConverter. By default, the converter is associated with application/rss+xml and application/atom+xml. An RSS feed might instead have a media type of text/xml, for example. The following code illustrates how to set the media type.

// Set the alternate mime type for the message converter
SyndFeedHttpMessageConverter syndFeedConverter = new SyndFeedHttpMessageConverter();
syndFeedConverter.setSupportedMediaTypes(Collections.singletonList(MediaType.TEXT_XML));

// Create a new RestTemplate instance
RestTemplate restTemplate = new RestTemplate();

// Add the ROME message converter
restTemplate.getMessageConverters().add(syndFeedConverter);

// Make the HTTP GET request, marshaling the response to a SyndFeed object
SyndFeed feed = restTemplate.getForObject(url, SyndFeed.class);
		

2.7.7 HTTP Basic Authentication

This example illustrates how to populate the HTTP Basic Authentication header with the username and password. If the username and password are accepted, then you will receive the response from the request. If they are not accepted, then the server is supposed to return an HTTP 401 Unauthorized response. Internally, RestTemplate handles the response, then throws an HttpClientErrorException. By calling getStatusCode() on this exception, you can determine the exact cause and handle it appropriately.

// Set the username and password for creating a Basic Auth request
HttpAuthentication authHeader = new HttpBasicAuthentication(username, password);
HttpHeaders requestHeaders = new HttpHeaders();
requestHeaders.setAuthorization(authHeader);
HttpEntity<?> requestEntity = new HttpEntity<Object>(requestHeaders);

// Create a new RestTemplate instance
RestTemplate restTemplate = new RestTemplate();

// Add the String message converter
restTemplate.getMessageConverters().add(new StringHttpMessageConverter());

try {
    // Make the HTTP GET request to the Basic Auth protected URL
    ResponseEntity<Message> response = restTemplate.exchange(url, HttpMethod.GET, requestEntity, String.class);
    return response.getBody();
} catch (HttpClientErrorException e) {
    Log.e(TAG, e.getLocalizedMessage(), e);
    // Handle 401 Unauthorized response
}