Package java.net

Class HttpURLConnection

  • Direct Known Subclasses:
    HttpsURLConnection, HttpURLConnectionImpl
    public abstract class HttpURLConnection
extends URLConnection
    An URLConnection for HTTP (RFC 2616) used to send and receive data over the web. Data may be of any type and length. This class may be used to send and receive streaming data whose length is not known in advance.

    Uses of this class follow a pattern:

    1. Obtain a new HttpURLConnection by calling URL.openConnection() and casting the result to HttpURLConnection.
    2. Prepare the request. The primary property of a request is its URI. Request headers may also include metadata such as credentials, preferred content types, and session cookies.
    3. Optionally upload a request body. Instances must be configured with setDoOutput(true) if they include a request body. Transmit data by writing to the stream returned by URLConnection.getOutputStream().
    4. Read the response. Response headers typically include metadata such as the response body's content type and length, modified dates and session cookies. The response body may be read from the stream returned by URLConnection.getInputStream(). If the response has no body, that method returns an empty stream.
    5. Disconnect. Once the response body has been read, the HttpURLConnection should be closed by calling disconnect(). Disconnecting releases the resources held by a connection so they may be closed or reused.

    For example, to retrieve the webpage at http://www.android.com/: 

       
   URL url = new URL("http://www.android.com/");
   HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
   try {
     InputStream in = new BufferedInputStream(urlConnection.getInputStream());
     readStream(in);
   } finally {
     urlConnection.disconnect();
   }

    Secure Communication with HTTPS

    Calling URL.openConnection() on a URL with the "https" scheme will return an HttpsURLConnection, which allows for overriding the default HostnameVerifier and SSLSocketFactory. An application-supplied SSLSocketFactory created from an SSLContext can provide a custom X509TrustManager for verifying certificate chains and a custom X509KeyManager for supplying client certificates. See HttpsURLConnection for more details.

    Response Handling

    HttpURLConnection will follow up to twenty HTTP redirects from KitKat onwards. Before KitKat it will only follow five. It will follow redirects from one origin server to another. This implementation doesn't follow redirects from HTTPS to HTTP or vice versa.

    If the HTTP response indicates that an error occurred, URLConnection.getInputStream() will throw an IOException. Use getErrorStream() to read the error response. The headers can be read in the normal way using URLConnection.getHeaderFields().

    Posting Content

    To upload data to a web server, configure the connection for output using setDoOutput(true).

    For best performance, you should call either setFixedLengthStreamingMode(int) when the body length is known in advance, or setChunkedStreamingMode(int) when it is not. Otherwise HttpURLConnection will be forced to buffer the complete request body in memory before it is transmitted, wasting (and possibly exhausting) heap and increasing latency.

    For example, to perform an upload: 

       
   HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
   try {
     urlConnection.setDoOutput(true);
     urlConnection.setChunkedStreamingMode(0);

     OutputStream out = new BufferedOutputStream(urlConnection.getOutputStream());
     writeStream(out);

     InputStream in = new BufferedInputStream(urlConnection.getInputStream());
     readStream(in);
   } finally {
     urlConnection.disconnect();
   }

    Performance

    The input and output streams returned by this class are not buffered. Most callers should wrap the returned streams with BufferedInputStream or BufferedOutputStream. Callers that do only bulk reads or writes may omit buffering.

    When transferring large amounts of data to or from a server, use streams to limit how much data is in memory at once. Unless you need the entire body to be in memory at once, process it as a stream (rather than storing the complete body as a single byte array or string).

    To reduce latency, this class may reuse the same underlying Socket for multiple request/response pairs. As a result, HTTP connections may be held open longer than necessary. Calls to disconnect() may return the socket to a pool of connected sockets. This behavior can be disabled by setting the http.keepAlive system property to false before issuing any HTTP requests. The http.maxConnections property may be used to control how many idle connections to each server will be held.

    By default, this implementation of HttpURLConnection requests that servers use gzip compression and it automatically decompresses the data for callers of URLConnection.getInputStream(). The Content-Encoding and Content-Length response headers are cleared in this case. Gzip compression can be disabled by setting the acceptable encodings in the request header: 

       
   urlConnection.setRequestProperty("Accept-Encoding", "identity");

    Setting the Accept-Encoding request header explicitly disables automatic decompression and leaves the response headers intact; callers must handle decompression as needed, according to the Content-Encoding header of the response.

    URLConnection.getContentLength() returns the number of bytes transmitted and cannot be used to predict how many bytes can be read from URLConnection.getInputStream() for compressed streams. Instead, read that stream until it is exhausted, i.e. when InputStream.read() returns -1.

    Handling Network Sign-On

    Some Wi-Fi networks block Internet access until the user clicks through a sign-on page. Such sign-on pages are typically presented by using HTTP redirects. You can use URLConnection.getURL() to test if your connection has been unexpectedly redirected. This check is not valid until after the response headers have been received, which you can trigger by calling URLConnection.getHeaderFields() or URLConnection.getInputStream(). For example, to check that a response was not redirected to an unexpected host: 

       
   HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
   try {
     InputStream in = new BufferedInputStream(urlConnection.getInputStream());
     if (!url.getHost().equals(urlConnection.getURL().getHost())) {
       // we were redirected! Kick the user out to the browser to sign on?
     }
     ...
   } finally {
     urlConnection.disconnect();
   }

    HTTP Authentication

    HttpURLConnection supports HTTP basic authentication. Use Authenticator to set the VM-wide authentication handler: 

       
   Authenticator.setDefault(new Authenticator() {
     protected PasswordAuthentication getPasswordAuthentication() {
       return new PasswordAuthentication(username, password.toCharArray());
     }
   });

    Unless paired with HTTPS, this is not a secure mechanism for user authentication. In particular, the username, password, request and response are all transmitted over the network without encryption.

    Sessions with Cookies

    To establish and maintain a potentially long-lived session between client and server, HttpURLConnection includes an extensible cookie manager. Enable VM-wide cookie management using CookieHandler and CookieManager: 

       
   CookieManager cookieManager = new CookieManager();
   CookieHandler.setDefault(cookieManager);

    By default, CookieManager accepts cookies from the origin server only. Two other policies are included: CookiePolicy.ACCEPT_ALL and CookiePolicy.ACCEPT_NONE. Implement CookiePolicy to define a custom policy.

    The default CookieManager keeps all accepted cookies in memory. It will forget these cookies when the VM exits. Implement CookieStore to define a custom cookie store.

    In addition to the cookies set by HTTP responses, you may set cookies programmatically. To be included in HTTP request headers, cookies must have the domain and path properties set.

    By default, new instances of HttpCookie work only with servers that support RFC 2965 cookies. Many web servers support only the older specification, RFC 2109. For compatibility with the most web servers, set the cookie version to 0.

    For example, to receive www.twitter.com in French: 

       
   HttpCookie cookie = new HttpCookie("lang", "fr");
   cookie.setDomain("twitter.com");
   cookie.setPath("/");
   cookie.setVersion(0);
   cookieManager.getCookieStore().add(new URI("http://twitter.com/"), cookie);

    HTTP Methods

    HttpURLConnection uses the GET method by default. It will use POST if setDoOutput(true) has been called. Other HTTP methods (OPTIONS, HEAD, PUT, DELETE and TRACE) can be used with setRequestMethod(java.lang.String).

    Proxies

    By default, this class will connect directly to the origin server. It can also connect via an HTTP or SOCKS proxy. To use a proxy, use URL.openConnection(Proxy) when creating the connection.

    IPv6 Support

    This class includes transparent support for IPv6. For hosts with both IPv4 and IPv6 addresses, it will attempt to connect to each of a host's addresses until a connection is established.

    Response Caching

    Android 4.0 (Ice Cream Sandwich, API level 15) includes a response cache. See android.net.http.HttpResponseCache for instructions on enabling HTTP caching in your application.

    Avoiding Bugs In Earlier Releases

    Prior to Android 2.2 (Froyo), this class had some frustrating bugs. In particular, calling close() on a readable InputStream could poison the connection pool. Work around this by disabling connection pooling: 

       
   private void disableConnectionReuseIfNecessary() {
     // Work around pre-Froyo bugs in HTTP connection reuse.
     if (Integer.parseInt(Build.VERSION.SDK) < Build.VERSION_CODES.FROYO) &#123;
       System.setProperty("http.keepAlive", "false");
     &#125;
   &#125;

    Each instance of HttpURLConnection may be used for one request/response pair. Instances of this class are not thread safe.

    • Field Detail

      • method

        protected String method
        The HTTP request method of this HttpURLConnection. The default value is "GET".

      • responseCode

        protected int responseCode
        The status code of the response obtained from the HTTP request. The default value is -1.

      • 1xx: Informational
      • 2xx: Success
      • 3xx: Relocation/Redirection
      • 4xx: Client Error
      • 5xx: Server Error

  • Constructor Detail

    • HttpURLConnection

      protected HttpURLConnection​(URL url)
      Constructs a new HttpURLConnection instance pointing to the resource specified by the url.
      Parameters:
      url - the URL of this connection.
      See Also:
      URL, URLConnection

  • Method Detail

    • disconnect

      public abstract void disconnect()
      Releases this connection so that its resources may be either reused or closed.

      Unlike other Java implementations, this will not necessarily close socket connections that can be reused. You can disable all connection reuse by setting the http.keepAlive system property to false before issuing any HTTP requests.

    • getErrorStream

      public InputStream getErrorStream()
      Returns an input stream from the server in the case of an error such as the requested file has not been found on the remote server. This stream can be used to read the data the server will send back.
      Returns:
      the error input stream returned by the server.

    • getFollowRedirects

      public static boolean getFollowRedirects()
      Returns the value of followRedirects which indicates if this connection follows a different URL redirected by the server. It is enabled by default.
      Returns:
      the value of the flag.
      See Also:
      setFollowRedirects(boolean)

    • getPermission

      public Permission getPermission()
                         throws IOException
      Returns the permission object (in this case SocketPermission) with the host and the port number as the target name and "resolve, connect" as the action list. If the port number of this URL instance is lower than 0 the port will be set to 80.
      Overrides:
      getPermission in class URLConnection
      Returns:
      the permission object required for this connection.
      Throws:
      IOException - if an IO exception occurs during the creation of the permission object.

    • getRequestMethod

      public String getRequestMethod()
      Returns the request method which will be used to make the request to the remote HTTP server. All possible methods of this HTTP implementation is listed in the class definition.
      Returns:
      the request method string.
      See Also:
      method, setRequestMethod(java.lang.String)

    • getResponseCode

      public int getResponseCode()
                    throws IOException
      Returns the response code returned by the remote HTTP server.
      Returns:
      the response code, -1 if no valid response code.
      Throws:
      IOException - if there is an IO error during the retrieval.
      See Also:
      getResponseMessage()

    • getResponseMessage

      public String getResponseMessage()
                          throws IOException
      Returns the response message returned by the remote HTTP server.
      Returns:
      the response message. null if no such response exists.
      Throws:
      IOException - if there is an error during the retrieval.
      See Also:
      getResponseCode()

    • setFollowRedirects

      public static void setFollowRedirects​(boolean auto)
      Sets the flag of whether this connection will follow redirects returned by the remote server.
      Parameters:
      auto - the value to enable or disable this option.

    • setRequestMethod

      public void setRequestMethod​(String method)
                      throws ProtocolException
      Sets the request command which will be sent to the remote HTTP server. This method can only be called before the connection is made.
      Parameters:
      method - the string representing the method to be used.
      Throws:
      ProtocolException - if this is called after connected, or the method is not supported by this HTTP implementation.
      See Also:
      getRequestMethod(), method

    • usingProxy

      public abstract boolean usingProxy()
      Returns whether this connection uses a proxy server or not.
      Returns:
      true if this connection passes a proxy server, false otherwise.

    • getContentEncoding

      public String getContentEncoding()
      Returns the encoding used to transmit the response body over the network. This is null or "identity" if the content was not encoded, or "gzip" if the body was gzip compressed. Most callers will be more interested in the content type, which may also include the content's character encoding.
      Overrides:
      getContentEncoding in class URLConnection
      Returns:
      the value of the response header field content-encoding.

    • getInstanceFollowRedirects

      public boolean getInstanceFollowRedirects()
      Returns whether this connection follows redirects.
      Returns:
      true if this connection follows redirects, false otherwise.

    • setInstanceFollowRedirects

      public void setInstanceFollowRedirects​(boolean followRedirects)
      Sets whether this connection follows redirects.
      Parameters:
      followRedirects - true if this connection will follows redirects, false otherwise.

    • getHeaderFieldDate

      public long getHeaderFieldDate​(String field,
                               long defaultValue)
      Returns the date value in milliseconds since 01.01.1970, 00:00h corresponding to the header field field. The defaultValue will be returned if no such field can be found in the response header.
      Overrides:
      getHeaderFieldDate in class URLConnection
      Parameters:
      field - the header field name.
      defaultValue - the default value to use if the specified header field wont be found.
      Returns:
      the header field represented in milliseconds since January 1, 1970 GMT.

    • setFixedLengthStreamingMode

      public void setFixedLengthStreamingMode​(long contentLength)
      Configures this connection to stream the request body with the known fixed byte count of contentLength.
      Parameters:
      contentLength - the fixed length of the HTTP request body.
      Throws:
      IllegalStateException - if already connected or another mode already set.
      IllegalArgumentException - if contentLength is less than zero.
      Since:
      1.7
      See Also:
      setChunkedStreamingMode(int)

    • setFixedLengthStreamingMode

      public void setFixedLengthStreamingMode​(int contentLength)
      Equivalent to setFixedLengthStreamingMode((long) contentLength), but available on earlier versions of Android and limited to 2 GiB.

    • setChunkedStreamingMode

      public void setChunkedStreamingMode​(int chunkLength)
      Stream a request body whose length is not known in advance. Old HTTP/1.0 only servers may not support this mode.

      When HTTP chunked encoding is used, the stream is divided into chunks, each prefixed with a header containing the chunk's size. A large chunk length requires a large internal buffer, potentially wasting memory. A small chunk length increases the number of bytes that must be transmitted because of the header on every chunk.

      Implementation details: In some releases the chunkLength is treated as a hint: chunks sent to the server may actually be larger or smaller. To force a chunk to be sent to the server call OutputStream.flush().

      Parameters:
      chunkLength - the length to use, or 0 for the default chunk length.
      Throws:
      IllegalStateException - if already connected or another mode already set.
      See Also:
      setFixedLengthStreamingMode(long)