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Android Reference

URLConnection


java.net

Class URLConnection

  • Direct Known Subclasses:
    HttpURLConnection, JarURLConnection


    public abstract class URLConnection
    extends Object
    A connection to a URL for reading or writing. For HTTP connections, see HttpURLConnection for documentation of HTTP-specific features.

    For example, to retrieve ftp://mirror.csclub.uwaterloo.ca/index.html:

       URL url = new URL("ftp://mirror.csclub.uwaterloo.ca/index.html");
       URLConnection urlConnection = url.openConnection();
       InputStream in = new BufferedInputStream(urlConnection.getInputStream());
       try {
         readStream(in);
       } finally {
         in.close();
       }
     

    URLConnection must be configured before it has connected to the remote resource. Instances of URLConnection are not reusable: you must use a different instance for each connection to a resource.

    Timeouts

    URLConnection supports two timeouts: a connect timeout and a read timeout. By default, operations never time out.

    Built-in Protocols

    • File
      Resources from the local file system can be loaded using file: URIs. File connections can only be used for input.
    • FTP
      File Transfer Protocol (RFC 959) is supported, but with no public subclass. FTP connections can be used for input or output but not both.

      By default, FTP connections will be made using anonymous as the username and the empty string as the password. Specify alternate usernames and passwords in the URL: ftp://username:password@host/path.

    • HTTP and HTTPS
      Refer to the HttpURLConnection and HttpsURLConnection subclasses.
    • Jar
      Refer to the JarURLConnection subclass.

    Registering Additional Protocols

    Use URL.setURLStreamHandlerFactory(java.net.URLStreamHandlerFactory) to register handlers for other protocol types.
    • Field Summary

      Fields
      Modifier and Type Field and Description
      protected boolean allowUserInteraction
      Unused by Android.
      protected boolean connected
      Specifies whether this URLConnection is already connected to the remote resource.
      protected boolean doInput
      Specifies whether this URLConnection allows receiving data.
      protected boolean doOutput
      Specifies whether this URLConnection allows sending data.
      protected long ifModifiedSince
      The data must be modified more recently than this time in milliseconds since January 1, 1970, GMT to be transmitted.
      protected URL url
      The URL which represents the remote target of this URLConnection.
      protected boolean useCaches
      Specifies whether the using of caches is enabled or the data has to be recent for every request.
    • Constructor Summary

      Constructors
      Modifier Constructor and Description
      protected URLConnection(URL url)
      Creates a new URLConnection instance pointing to the resource specified by the given URL.
    • Field Detail

      • url

        protected URL url
        The URL which represents the remote target of this URLConnection.
      • ifModifiedSince

        protected long ifModifiedSince
        The data must be modified more recently than this time in milliseconds since January 1, 1970, GMT to be transmitted.
      • useCaches

        protected boolean useCaches
        Specifies whether the using of caches is enabled or the data has to be recent for every request.
      • connected

        protected boolean connected
        Specifies whether this URLConnection is already connected to the remote resource. If this field is set to true the flags for setting up the connection are not changeable anymore.
      • doOutput

        protected boolean doOutput
        Specifies whether this URLConnection allows sending data.
      • doInput

        protected boolean doInput
        Specifies whether this URLConnection allows receiving data.
    • Constructor Detail

      • URLConnection

        protected URLConnection(URL url)
        Creates a new URLConnection instance pointing to the resource specified by the given URL.
        Parameters:
        url - the URL which represents the resource this URLConnection will point to.
    • Method Detail

      • connect

        public abstract void connect()
                              throws IOException
        Opens a connection to the resource. This method will not reconnect to a resource after the initial connection has been closed.
        Throws:
        IOException - if an error occurs while connecting to the resource.
      • getAllowUserInteraction

        public boolean getAllowUserInteraction()
        Returns allowUserInteraction. Unused by Android.
      • getContent

        public Object getContent()
                          throws IOException
        Returns an object representing the content of the resource this URLConnection is connected to. First, it attempts to get the content type from the method getContentType() which looks at the response header field "Content-Type". If none is found it will guess the content type from the filename extension. If that fails the stream itself will be used to guess the content type.
        Returns:
        the content representing object.
        Throws:
        IOException - if an error occurs obtaining the content.
      • getContent

        public Object getContent(Class[] types)
                          throws IOException
        Returns an object representing the content of the resource this URLConnection is connected to. First, it attempts to get the content type from the method getContentType() which looks at the response header field "Content-Type". If none is found it will guess the content type from the filename extension. If that fails the stream itself will be used to guess the content type. The content type must match with one of the list types.
        Parameters:
        types - the list of acceptable content types.
        Returns:
        the content representing object or null if the content type does not match with one of the specified types.
        Throws:
        IOException - if an error occurs obtaining the content.
      • getContentEncoding

        public String getContentEncoding()
        Returns the content encoding type specified by the response header field content-encoding or null if this field is not set.
        Returns:
        the value of the response header field content-encoding.
      • getContentLength

        public int getContentLength()
        Returns the content length in bytes specified by the response header field content-length or -1 if this field is not set.
        Returns:
        the value of the response header field content-length.
      • getContentType

        public String getContentType()
        Returns the MIME-type of the content specified by the response header field content-type or null if type is unknown.
        Returns:
        the value of the response header field content-type.
      • getDate

        public long getDate()
        Returns the timestamp when this response has been sent as a date in milliseconds since January 1, 1970 GMT or 0 if this timestamp is unknown.
        Returns:
        the sending timestamp of the current response.
      • getDefaultAllowUserInteraction

        public static boolean getDefaultAllowUserInteraction()
        Returns the default value of allowUserInteraction. Unused by Android.
      • getDefaultUseCaches

        public boolean getDefaultUseCaches()
        Returns the default setting whether this connection allows using caches.
        Returns:
        the value of the default setting defaultUseCaches.
        See Also:
        useCaches
      • getDoInput

        public boolean getDoInput()
        Returns the value of the option doInput which specifies whether this connection allows to receive data.
        Returns:
        true if this connection allows input, false otherwise.
        See Also:
        doInput
      • getDoOutput

        public boolean getDoOutput()
        Returns the value of the option doOutput which specifies whether this connection allows to send data.
        Returns:
        true if this connection allows output, false otherwise.
        See Also:
        doOutput
      • getExpiration

        public long getExpiration()
        Returns the timestamp when this response will be expired in milliseconds since January 1, 1970 GMT or 0 if this timestamp is unknown.
        Returns:
        the value of the response header field expires.
      • getFileNameMap

        public static FileNameMap getFileNameMap()
        Returns the table which is used by all URLConnection instances to determine the MIME-type according to a file extension.
        Returns:
        the file name map to determine the MIME-type.
      • getHeaderField

        public String getHeaderField(int pos)
        Returns the header value at the field position pos or null if the header has fewer than pos fields. The base implementation of this method returns always null.

        Some implementations (notably HttpURLConnection) include a mapping for the null key; in HTTP's case, this maps to the HTTP status line and is treated as being at position 0 when indexing into the header fields.

        Parameters:
        pos - the field position of the response header.
        Returns:
        the value of the field at position pos.
      • getHeaderFields

        public Map<String,List<String>> getHeaderFields()
        Returns an unmodifiable map of the response-header fields and values. The response-header field names are the key values of the map. The map values are lists of header field values associated with a particular key name.

        Some implementations (notably HttpURLConnection) include a mapping for the null key; in HTTP's case, this maps to the HTTP status line and is treated as being at position 0 when indexing into the header fields.

        Returns:
        the response-header representing generic map.
        Since:
        1.4
      • getRequestProperties

        public Map<String,List<String>> getRequestProperties()
        Returns an unmodifiable map of general request properties used by this connection. The request property names are the key values of the map. The map values are lists of property values of the corresponding key name.
        Returns:
        the request-property representing generic map.
        Since:
        1.4
      • addRequestProperty

        public void addRequestProperty(String field,
                              String newValue)
        Adds the given property to the request header. Existing properties with the same name will not be overwritten by this method.
        Parameters:
        field - the request property field name to add.
        newValue - the value of the property which is to add.
        Throws:
        IllegalStateException - if the connection has been already established.
        NullPointerException - if the property name is null.
        Since:
        1.4
      • getHeaderField

        public String getHeaderField(String key)
        Returns the value of the header field specified by key or null if there is no field with this name. The base implementation of this method returns always null.

        Some implementations (notably HttpURLConnection) include a mapping for the null key; in HTTP's case, this maps to the HTTP status line and is treated as being at position 0 when indexing into the header fields.

        Parameters:
        key - the name of the header field.
        Returns:
        the value of the header field.
      • getHeaderFieldDate

        public long getHeaderFieldDate(String field,
                              long defaultValue)
        Returns the specified header value as a date in milliseconds since January 1, 1970 GMT. Returns the defaultValue if no such header field could be found.
        Parameters:
        field - the header field name whose value is needed.
        defaultValue - the default value if no field has been found.
        Returns:
        the value of the specified header field as a date in milliseconds.
      • getHeaderFieldInt

        public int getHeaderFieldInt(String field,
                            int defaultValue)
        Returns the specified header value as a number. Returns the defaultValue if no such header field could be found or the value could not be parsed as an Integer.
        Parameters:
        field - the header field name whose value is needed.
        defaultValue - the default value if no field has been found.
        Returns:
        the value of the specified header field as a number.
      • getHeaderFieldKey

        public String getHeaderFieldKey(int posn)
        Returns the name of the header field at the given position posn or null if there are fewer than posn fields. The base implementation of this method returns always null.

        Some implementations (notably HttpURLConnection) include a mapping for the null key; in HTTP's case, this maps to the HTTP status line and is treated as being at position 0 when indexing into the header fields.

        Parameters:
        posn - the position of the header field which has to be returned.
        Returns:
        the header field name at the given position.
      • getIfModifiedSince

        public long getIfModifiedSince()
        Returns the point of time since when the data must be modified to be transmitted. Some protocols transmit data only if it has been modified more recently than a particular time.
        Returns:
        the time in milliseconds since January 1, 1970 GMT.
        See Also:
        ifModifiedSince
      • getInputStream

        public InputStream getInputStream()
                                   throws IOException
        Returns an InputStream for reading data from the resource pointed by this URLConnection. It throws an UnknownServiceException by default. This method must be overridden by its subclasses.
        Returns:
        the InputStream to read data from.
        Throws:
        IOException - if no InputStream could be created.
      • getLastModified

        public long getLastModified()
        Returns the value of the response header field last-modified or 0 if this value is not set.
        Returns:
        the value of the last-modified header field.
      • getOutputStream

        public OutputStream getOutputStream()
                                     throws IOException
        Returns an OutputStream for writing data to this URLConnection. It throws an UnknownServiceException by default. This method must be overridden by its subclasses.
        Returns:
        the OutputStream to write data.
        Throws:
        IOException - if no OutputStream could be created.
      • getPermission

        public Permission getPermission()
                                 throws IOException
        Returns a Permission object representing all needed permissions to open this connection. The returned permission object depends on the state of the connection and will be null if no permissions are necessary. By default, this method returns AllPermission. Subclasses should overwrite this method to return an appropriate permission object.
        Returns:
        the permission object representing the needed permissions to open this connection.
        Throws:
        IOException - if an I/O error occurs while creating the permission object.
      • getRequestProperty

        public String getRequestProperty(String field)
        Returns the value of the request header property specified by {code field} or null if there is no field with this name. The base implementation of this method returns always null.
        Parameters:
        field - the name of the request header property.
        Returns:
        the value of the property.
        Throws:
        IllegalStateException - if the connection has been already established.
      • getURL

        public URL getURL()
        Returns the URL represented by this URLConnection.
        Returns:
        the URL of this connection.
      • getUseCaches

        public boolean getUseCaches()
        Returns the value of the flag which specifies whether this URLConnection allows to use caches.
        Returns:
        true if using caches is allowed, false otherwise.
      • guessContentTypeFromName

        public static String guessContentTypeFromName(String url)
        Determines the MIME-type of the given resource url by resolving the filename extension with the internal FileNameMap. Any fragment identifier is removed before processing.
        Parameters:
        url - the URL with the filename to get the MIME type.
        Returns:
        the guessed content type or null if the type could not be determined.
      • guessContentTypeFromStream

        public static String guessContentTypeFromStream(InputStream is)
                                                 throws IOException
        Determines the MIME-type of the resource represented by the input stream is by reading its first few characters.
        Parameters:
        is - the resource representing input stream to determine the content type.
        Returns:
        the guessed content type or null if the type could not be determined.
        Throws:
        IOException - if an I/O error occurs while reading from the input stream.
      • setAllowUserInteraction

        public void setAllowUserInteraction(boolean newValue)
        Sets allowUserInteraction. Unused by Android.
      • setContentHandlerFactory

        public static void setContentHandlerFactory(ContentHandlerFactory contentFactory)
        Sets the internally used content handler factory. The content factory can only be set once during the lifetime of the application.
        Parameters:
        contentFactory - the content factory to be set.
        Throws:
        Error - if the factory has been already set.
      • setDefaultAllowUserInteraction

        public static void setDefaultAllowUserInteraction(boolean allows)
        Sets the default value for allowUserInteraction. Unused by Android.
      • setDefaultUseCaches

        public void setDefaultUseCaches(boolean newValue)
        Sets the default value for the flag indicating whether this connection allows to use caches. Existing URLConnections are unaffected.
        Parameters:
        newValue - the default value of the flag to be used for new connections.
        See Also:
        useCaches
      • setDoInput

        public void setDoInput(boolean newValue)
        Sets the flag indicating whether this URLConnection allows input. It cannot be set after the connection is established.
        Parameters:
        newValue - the new value for the flag to be set.
        Throws:
        IllegalAccessError - if this method attempts to change the value after the connection has been already established.
        See Also:
        doInput
      • setDoOutput

        public void setDoOutput(boolean newValue)
        Sets the flag indicating whether this URLConnection allows output. It cannot be set after the connection is established.
        Parameters:
        newValue - the new value for the flag to be set.
        Throws:
        IllegalAccessError - if this method attempts to change the value after the connection has been already established.
        See Also:
        doOutput
      • setFileNameMap

        public static void setFileNameMap(FileNameMap map)
        Sets the internal map which is used by all URLConnection instances to determine the MIME-type according to a filename extension.
        Parameters:
        map - the MIME table to be set.
      • setIfModifiedSince

        public void setIfModifiedSince(long newValue)
        Sets the point of time since when the data must be modified to be transmitted. Some protocols transmit data only if it has been modified more recently than a particular time. The data will be transmitted regardless of its timestamp if this option is set to 0.
        Parameters:
        newValue - the time in milliseconds since January 1, 1970 GMT.
        Throws:
        IllegalStateException - if this URLConnection has already been connected.
        See Also:
        ifModifiedSince
      • setRequestProperty

        public void setRequestProperty(String field,
                              String newValue)
        Sets the value of the specified request header field. The value will only be used by the current URLConnection instance. This method can only be called before the connection is established.
        Parameters:
        field - the request header field to be set.
        newValue - the new value of the specified property.
        Throws:
        IllegalStateException - if the connection has been already established.
        NullPointerException - if the parameter field is null.
      • setUseCaches

        public void setUseCaches(boolean newValue)
        Sets the flag indicating whether this connection allows to use caches or not. This method can only be called prior to the connection establishment.
        Parameters:
        newValue - the value of the flag to be set.
        Throws:
        IllegalStateException - if this method attempts to change the flag after the connection has been established.
        See Also:
        useCaches
      • setConnectTimeout

        public void setConnectTimeout(int timeoutMillis)
        Sets the maximum time in milliseconds to wait while connecting. Connecting to a server will fail with a SocketTimeoutException if the timeout elapses before a connection is established. The default value of 0 causes us to do a blocking connect. This does not mean we will never time out, but it probably means you'll get a TCP timeout after several minutes.

        Warning: if the hostname resolves to multiple IP addresses, this client will try each in RFC 3484 order. If connecting to each of these addresses fails, multiple timeouts will elapse before the connect attempt throws an exception. Host names that support both IPv6 and IPv4 always have at least 2 IP addresses.

        Throws:
        IllegalArgumentException - if timeoutMillis &lt; 0.
      • getConnectTimeout

        public int getConnectTimeout()
        Returns the connect timeout in milliseconds. (See {#setConnectTimeout}.)
      • setReadTimeout

        public void setReadTimeout(int timeoutMillis)
        Sets the maximum time to wait for an input stream read to complete before giving up. Reading will fail with a SocketTimeoutException if the timeout elapses before data becomes available. The default value of 0 disables read timeouts; read attempts will block indefinitely.
        Parameters:
        timeoutMillis - the read timeout in milliseconds. Non-negative.
      • getReadTimeout

        public int getReadTimeout()
        Returns the read timeout in milliseconds, or 0 if reads never timeout.
      • toString

        public String toString()
        Returns the string representation containing the name of this class and the URL.
        Overrides:
        toString in class Object
        Returns:
        the string representation of this URLConnection instance.


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