Package com.google.gwt.http.client

See:
          Description

Package com.google.gwt.http.client Description

Provides the client-side classes and interfaces for making HTTP requests and processing the associated responses.

Most applications will be interested in the Request, RequestBuilder, RequestCallback and Response classes.

Caveats

Same-Origin Security Policy

Pending Request Limit

Required Module

<module>
  <!-- other inherited modules, such as com.google.gwt.user.User -->
  <inherits name="com.google.gwt.http.HTTP"/>
  <!-- additional module settings -->
</module>

Quick Howto's

How should I write a RequestCallback handler class?

public class RequestCallbackExample implements RequestCallback {

  private static final int STATUS_CODE_OK = 200;

  public void onError(Request request, Throwable exception) {
    if (exception instanceof RequestTimeoutException) {
      // handle a request timeout
    } else {
      // handle other request errors
    }
  }

  public void onResponseReceived(Request request, Response response) {
    if (STATUS_CODE_OK == response.getStatusCode()) {
      // handle OK response from the server 
    } else {
      // handle non-OK response from the server
    }
  }
}

How do I make a GET request?

public class GetExample implements EntryPoint {
  public static final int STATUS_CODE_OK = 200;
  
  public static void doGet(String url) {
    RequestBuilder builder = new RequestBuilder(RequestBuilder.GET, url);

    try {
      Request response = builder.sendRequest(null, new RequestCallback() {
        public void onError(Request request, Throwable exception) {
          // Code omitted for clarity
        }

        public void onResponseReceived(Request request, Response response) {
          // Code omitted for clarity
        }
      });
    } catch (RequestException e) {
      // Code omitted for clarity
    }
  }

  public void onModuleLoad() {
    doGet("/");
  }
}

How do I make a POST request?

public class PostExample {
  public static void doPost(String url, String postData) {
    RequestBuilder builder = new RequestBuilder(RequestBuilder.POST, url);

    try {
      builder.setHeader("Content-Type", "application/x-www-form-urlencoded");
      Request response = builder.sendRequest(postData, new RequestCallback() {

        public void onError(Request request, Throwable exception) {
          // code omitted for clarity
        }

        public void onResponseReceived(Request request, Response response) {
          // code omitted for clarity
        }
      });
    } catch (RequestException e) {
      Window.alert("Failed to send the request: " + e.getMessage());
    }
  }

  public void onModuleLoad() {
    doPost("/", "Hello World!");
  }
}

How do I use request timeouts?

public class TimeoutExample implements EntryPoint {
  public static void doGetWithTimeout(String url) {
    RequestBuilder builder = new RequestBuilder(RequestBuilder.GET, url);

    try {
      /*
       * wait 2000 milliseconds for the request to complete
       */
      builder.setTimeoutMillis(2000);
      
      Request response = builder.sendRequest(null, new RequestCallback() {
        public void onError(Request request, Throwable exception) {
          if (exception instanceof RequestTimeoutException) {
            // handle a request timeout
          } else {
            // handle other request errors
          }
        }

        public void onResponseReceived(Request request, Response response) {
          // code omitted for clarity
        }
      });
    } catch (RequestException e) {
      Window.alert("Failed to send the request: " + e.getMessage());
    }
  }

  public void onModuleLoad() {
    doGetWithTimeout("/");
  }
}

How do I construct a string for use in a query or POST body?

public class QueryAndFormDataExample {
  
  public static interface Entry {
    String getName();
    String getValue();
  }

  public static String buildQueryString(Entry[] queryEntries) {
    StringBuffer sb = new StringBuffer();

    for (int i = 0, n = queryEntries.length; i < n; ++i) {
      Entry queryEntry = queryEntries[i];

      if (i > 0) {
        sb.append("&");
      }

      // encode the characters in the name
      String encodedName = URL.encodeQueryString(queryEntry.getName());
      sb.append(encodedName);
      
      sb.append("=");
    
      // encode the characters in the value
      String encodedValue = URL.encodeQueryString(queryEntry.getValue());
      sb.append(encodedValue);
    }
    
    return sb.toString();
  }
}

How can I make a RequestBuilder send a request other than GET or POST?

public class RequestBuilderForAnyHTTPMethodTypeExample extends RequestBuilder {
  
  /**
   * Constructor that allows a developer to override the HTTP method 
   * restrictions imposed by the RequestBuilder class.  Note if you override the 
   * RequestBuilder's HTTP method restrictions in this manner, your application 
   * may not work correctly on Safari browsers.
   * 
   * @param httpMethod any non-null, non-empty string is considered valid
   * @param url any non-null, non-empty string is considered valid
   *
   * @throws IllegalArgumentException if httpMethod or url are empty
   * @throws NullPointerException if httpMethod or url are null
   */
  public RequestBuilderForAnyHTTPMethodTypeExample(String httpMethod, String url) {
    super(httpMethod, url);
  }
}