Class URLConnection

Method Details

• getFileNameMap

  public static FileNameMap getFileNameMap()

  Loads filename map (a mimetable) from a data file. It will first try to load the user-specific table, defined by "content.types.user.table" property. If that fails, it tries to load the default built-in table.

  Returns:

  the FileNameMap

  Since:

  1.2

  See Also:

  • setFileNameMap(java.net.FileNameMap)

• setFileNameMap

  public static void setFileNameMap(FileNameMap map)

  Sets the FileNameMap.

  If there is a security manager, this method first calls the security manager's checkSetFactory method to ensure the operation is allowed. This could result in a SecurityException.

  Parameters:

  map - the FileNameMap to be set

  Throws:

  SecurityException - if a security manager exists and its checkSetFactory method doesn't allow the operation.

  Since:

  1.2

  See Also:

  • SecurityManager.checkSetFactory()
  • getFileNameMap()

• connect

  public abstract void connect() throws IOException

  Opens a communications link to the resource referenced by this URL, if such a connection has not already been established.

  If the connect method is called when the connection has already been opened (indicated by the connected field having the value true), the call is ignored.

  URLConnection objects go through two phases: first they are created, then they are connected. After being created, and before being connected, various options can be specified (e.g., doInput and UseCaches). After connecting, it is an error to try to set them. Operations that depend on being connected, like getContentLength, will implicitly perform the connection, if necessary.

  Throws:

  SocketTimeoutException - if the timeout expires before the connection can be established

  IOException - if an I/O error occurs while opening the connection.

  See Also:

  • connected
  • getConnectTimeout()
  • setConnectTimeout(int)

• setConnectTimeout

  public void setConnectTimeout(int timeout)

  Sets a specified timeout value, in milliseconds, to be used when opening a communications link to the resource referenced by this URLConnection. If the timeout expires before the connection can be established, a java.net.SocketTimeoutException is raised. A timeout of zero is interpreted as an infinite timeout.

  Some non-standard implementation of this method may ignore the specified timeout. To see the connect timeout set, please call getConnectTimeout().

  Parameters:

  timeout - an int that specifies the connect timeout value in milliseconds

  Throws:

  IllegalArgumentException - if the timeout parameter is negative

  Since:

  1.5

  See Also:

  • getConnectTimeout()
  • connect()

• getConnectTimeout

  public int getConnectTimeout()

  Returns setting for connect timeout.

  0 return implies that the option is disabled (i.e., timeout of infinity).

  Returns:

  an int that indicates the connect timeout value in milliseconds

  Since:

  1.5

  See Also:

  • setConnectTimeout(int)
  • connect()

• setReadTimeout

  public void setReadTimeout(int timeout)

  Sets the read timeout to a specified timeout, in milliseconds. A non-zero value specifies the timeout when reading from Input stream when a connection is established to a resource. If the timeout expires before there is data available for read, a java.net.SocketTimeoutException is raised. A timeout of zero is interpreted as an infinite timeout.

  Some non-standard implementation of this method ignores the specified timeout. To see the read timeout set, please call getReadTimeout().

  Parameters:

  timeout - an int that specifies the timeout value to be used in milliseconds

  Throws:

  IllegalArgumentException - if the timeout parameter is negative

  Since:

  1.5

  See Also:

  • getReadTimeout()
  • InputStream.read()

• getReadTimeout

  public int getReadTimeout()

  Returns setting for read timeout. 0 return implies that the option is disabled (i.e., timeout of infinity).

  Returns:

  an int that indicates the read timeout value in milliseconds

  Since:

  1.5

  See Also:

  • setReadTimeout(int)
  • InputStream.read()

• getURL

  public URL getURL()

  Returns the value of this URLConnection's URL field.

  Returns:

  the value of this URLConnection's URL field.

  See Also:

  • url

• getContentLength

  public int getContentLength()

  Returns the value of the content-length header field.

  Note: getContentLengthLong() should be preferred over this method, since it returns a long instead and is therefore more portable.

  Returns:

  the content length of the resource that this connection's URL references, -1 if the content length is not known, or if the content length is greater than Integer.MAX_VALUE.

• getContentLengthLong

  public long getContentLengthLong()

  Returns the value of the content-length header field as a long.

  Returns:

  the content length of the resource that this connection's URL references, or -1 if the content length is not known.

  Since:

  1.7

• getContentType

  public String getContentType()

  Returns the value of the content-type header field.

  Returns:

  the content type of the resource that the URL references, or null if not known.

  See Also:

  • getHeaderField(java.lang.String)

• getContentEncoding

  public String getContentEncoding()

  Returns the value of the content-encoding header field.

  Returns:

  the content encoding of the resource that the URL references, or null if not known.

  See Also:

  • getHeaderField(java.lang.String)

• getExpiration

  public long getExpiration()

  Returns the value of the expires header field.

  Returns:

  the expiration date of the resource that this URL references, or 0 if not known. The value is the number of milliseconds since January 1, 1970 GMT.

  See Also:

  • getHeaderField(java.lang.String)

• getDate

  public long getDate()

  Returns the value of the date header field.

  Returns:

  the sending date of the resource that the URL references, or 0 if not known. The value returned is the number of milliseconds since January 1, 1970 GMT.

  See Also:

  • getHeaderField(java.lang.String)

• getLastModified

  public long getLastModified()

  Returns the value of the last-modified header field. The result is the number of milliseconds since January 1, 1970 GMT.

  Returns:

  the date the resource referenced by this URLConnection was last modified, or 0 if not known.

  See Also:

  • getHeaderField(java.lang.String)

• getHeaderField

  public String getHeaderField(String name)

  Returns the value of the named header field.

  If called on a connection that sets the same header multiple times with possibly different values, only the last value is returned.

  Parameters:

  name - the name of a header field.

  Returns:

  the value of the named header field, or null if there is no such field in the header.

• getHeaderFields

  public Map<String,List<String>> getHeaderFields()

  Returns an unmodifiable Map of the header fields. The Map keys are Strings that represent the response-header field names. Each Map value is an unmodifiable List of Strings that represents the corresponding field values.

  Returns:

  a Map of header fields

  Since:

  1.4

• getHeaderFieldInt

  public int getHeaderFieldInt(String name, int Default)

  Returns the value of the named field parsed as a number.

  This form of getHeaderField exists because some connection types (e.g., http-ng) have pre-parsed headers. Classes for that connection type can override this method and short-circuit the parsing.

  Parameters:

  name - the name of the header field.

  Default - the default value.

  Returns:

  the value of the named field, parsed as an integer. The Default value is returned if the field is missing or malformed.

• getHeaderFieldLong

  public long getHeaderFieldLong(String name, long Default)

  Returns the value of the named field parsed as a number.

  This form of getHeaderField exists because some connection types (e.g., http-ng) have pre-parsed headers. Classes for that connection type can override this method and short-circuit the parsing.

  Parameters:

  name - the name of the header field.

  Default - the default value.

  Returns:

  the value of the named field, parsed as a long. The Default value is returned if the field is missing or malformed.

  Since:

  1.7

• getHeaderFieldDate

  public long getHeaderFieldDate(String name, long Default)

  Returns the value of the named field parsed as date. The result is the number of milliseconds since January 1, 1970 GMT represented by the named field.

  This form of getHeaderField exists because some connection types (e.g., http-ng) have pre-parsed headers. Classes for that connection type can override this method and short-circuit the parsing.

  Parameters:

  name - the name of the header field.

  Default - a default value.

  Returns:

  the value of the field, parsed as a date. The value of the Default argument is returned if the field is missing or malformed.

• getHeaderFieldKey

  public String getHeaderFieldKey(int n)

  Returns the key for the n^th header field. Some implementations may treat the 0^th header field as special, in which case, getHeaderField(0) may return some value, but getHeaderFieldKey(0) returns null. For n > 0 it returns null if there are fewer than n+1 fields.

  Parameters:

  n - an index, where n>=0

  Returns:

  the key for the n^th header field, or null if there are fewer than n+1 fields when n > 0.

• getHeaderField

  public String getHeaderField(int n)

  Returns the value for the n^th header field. It returns null if there are fewer than n+1 fields.

  This method can be used in conjunction with the getHeaderFieldKey method to iterate through all the headers in the message.

  Parameters:

  n - an index, where n>=0

  Returns:

  the value of the n^th header field or null if there are fewer than n+1 fields

  See Also:

  • getHeaderFieldKey(int)

• getContent

  public Object getContent() throws IOException

  Retrieves the contents of this URL connection.

  This method first determines the content type of the object by calling the getContentType method. If this is the first time that the application has seen that specific content type, a content handler for that content type is created.

  This is done as follows:

  1. If the application has set up a content handler factory instance using the setContentHandlerFactory method, the createContentHandler method of that instance is called with the content type as an argument; the result is a content handler for that content type.
  2. If no ContentHandlerFactory has yet been set up, or if the factory's createContentHandler method returns null, then the ServiceLoader mechanism is used to locate ContentHandlerFactory implementations using the system class loader. The order that factories are located is implementation specific, and an implementation is free to cache the located factories. A ServiceConfigurationError, Error or RuntimeException thrown from the createContentHandler, if encountered, will be propagated to the calling thread. The createContentHandler method of each factory, if instantiated, is invoked, with the content type, until a factory returns non-null, or all factories have been exhausted.
  3. Failing that, this method tries to load a content handler class as defined by ContentHandler. If the class does not exist, or is not a subclass of ContentHandler, then an UnknownServiceException is thrown.

  Returns:

  the object fetched. The instanceof operator should be used to determine the specific kind of object returned.

  Throws:

  IOException - if an I/O error occurs while getting the content.

  UnknownServiceException - if the protocol does not support the content type.

  See Also:

  • ContentHandlerFactory.createContentHandler(java.lang.String)
  • getContentType()
  • setContentHandlerFactory(java.net.ContentHandlerFactory)

• getContent

  public Object getContent(Class<?>[] classes) throws IOException

  Retrieves the contents of this URL connection.

  Parameters:

  classes - the Class array indicating the requested types

  Returns:

  the object fetched that is the first match of the type specified in the classes array. null if none of the requested types are supported. The instanceof operator should be used to determine the specific kind of object returned.

  Throws:

  IOException - if an I/O error occurs while getting the content.

  UnknownServiceException - if the protocol does not support the content type.

  Since:

  1.3

  See Also:

  • getContent()
  • ContentHandlerFactory.createContentHandler(java.lang.String)
  • getContent(java.lang.Class[])
  • setContentHandlerFactory(java.net.ContentHandlerFactory)

• getPermission

  public Permission getPermission() throws IOException

  Returns a permission object representing the permission necessary to make the connection represented by this object. This method returns null if no permission is required to make the connection. By default, this method returns java.security.AllPermission. Subclasses should override this method and return the permission that best represents the permission required to make a connection to the URL. For example, a URLConnection representing a file: URL would return a java.io.FilePermission object.

  The permission returned may dependent upon the state of the connection. For example, the permission before connecting may be different from that after connecting. For example, an HTTP sever, say foo.com, may redirect the connection to a different host, say bar.com. Before connecting the permission returned by the connection will represent the permission needed to connect to foo.com, while the permission returned after connecting will be to bar.com.

  Permissions are generally used for two purposes: to protect caches of objects obtained through URLConnections, and to check the right of a recipient to learn about a particular URL. In the first case, the permission should be obtained after the object has been obtained. For example, in an HTTP connection, this will represent the permission to connect to the host from which the data was ultimately fetched. In the second case, the permission should be obtained and tested before connecting.

  Returns:

  the permission object representing the permission necessary to make the connection represented by this URLConnection.

  Throws:

  IOException - if the computation of the permission requires network or file I/O and an exception occurs while computing it.

• getInputStream

  public InputStream getInputStream() throws IOException

  Returns an input stream that reads from this open connection. A SocketTimeoutException can be thrown when reading from the returned input stream if the read timeout expires before data is available for read.

  Returns:

  an input stream that reads from this open connection.

  Throws:

  IOException - if an I/O error occurs while creating the input stream.

  UnknownServiceException - if the protocol does not support input.

  See Also:

  • setReadTimeout(int)
  • getReadTimeout()

• getOutputStream

  public OutputStream getOutputStream() throws IOException

  Returns an output stream that writes to this connection.

  Returns:

  an output stream that writes to this connection.

  Throws:

  IOException - if an I/O error occurs while creating the output stream.

  UnknownServiceException - if the protocol does not support output.

• toString

  public String toString()

  Returns a String representation of this URL connection.

  Overrides:

  toString in class Object

  Returns:

  a string representation of this URLConnection.

• setDoInput

  public void setDoInput(boolean doinput)

  Sets the value of the doInput field for this URLConnection to the specified value.

  A URL connection can be used for input and/or output. Set the doInput flag to true if you intend to use the URL connection for input, false if not. The default is true.

  Parameters:

  doinput - the new value.

  Throws:

  IllegalStateException - if already connected

  See Also:

  • doInput
  • getDoInput()

• getDoInput

  public boolean getDoInput()

  Returns the value of this URLConnection's doInput flag.

  Returns:

  the value of this URLConnection's doInput flag.

  See Also:

  • setDoInput(boolean)

• setDoOutput

  public void setDoOutput(boolean dooutput)

  Sets the value of the doOutput field for this URLConnection to the specified value.

  A URL connection can be used for input and/or output. Set the doOutput flag to true if you intend to use the URL connection for output, false if not. The default is false.

  Parameters:

  dooutput - the new value.

  Throws:

  IllegalStateException - if already connected

  See Also:

  • getDoOutput()

• getDoOutput

  public boolean getDoOutput()

  Returns the value of this URLConnection's doOutput flag.

  Returns:

  the value of this URLConnection's doOutput flag.

  See Also:

  • setDoOutput(boolean)

• setAllowUserInteraction

  public void setAllowUserInteraction(boolean allowuserinteraction)

  Set the value of the allowUserInteraction field of this URLConnection.

  Parameters:

  allowuserinteraction - the new value.

  Throws:

  IllegalStateException - if already connected

  See Also:

  • getAllowUserInteraction()

• getAllowUserInteraction

  public boolean getAllowUserInteraction()

  Returns the value of the allowUserInteraction field for this object.

  Returns:

  the value of the allowUserInteraction field for this object.

  See Also:

  • setAllowUserInteraction(boolean)

• setDefaultAllowUserInteraction

  public static void setDefaultAllowUserInteraction(boolean defaultallowuserinteraction)

  Sets the default value of the allowUserInteraction field for all future URLConnection objects to the specified value.

  Parameters:

  defaultallowuserinteraction - the new value.

  See Also:

  • getDefaultAllowUserInteraction()

• getDefaultAllowUserInteraction

  public static boolean getDefaultAllowUserInteraction()

  Returns the default value of the allowUserInteraction field.

  This default is "sticky", being a part of the static state of all URLConnections. This flag applies to the next, and all following URLConnections that are created.

  Returns:

  the default value of the allowUserInteraction field.

  See Also:

  • setDefaultAllowUserInteraction(boolean)

• setUseCaches

  public void setUseCaches(boolean usecaches)

  Sets the value of the useCaches field of this URLConnection to the specified value.

  Some protocols do caching of documents. Occasionally, it is important to be able to "tunnel through" and ignore the caches (e.g., the "reload" button in a browser). If the UseCaches flag on a connection is true, the connection is allowed to use whatever caches it can. If false, caches are to be ignored. The default value comes from defaultUseCaches, which defaults to true. A default value can also be set per-protocol using setDefaultUseCaches(String,boolean).

  Parameters:

  usecaches - a boolean indicating whether or not to allow caching

  Throws:

  IllegalStateException - if already connected

  See Also:

  • getUseCaches()

• getUseCaches

  public boolean getUseCaches()

  Returns the value of this URLConnection's useCaches field.

  Returns:

  the value of this URLConnection's useCaches field.

  See Also:

  • setUseCaches(boolean)

• setIfModifiedSince

  public void setIfModifiedSince(long ifmodifiedsince)

  Sets the value of the ifModifiedSince field of this URLConnection to the specified value.

  Parameters:

  ifmodifiedsince - the new value.

  Throws:

  IllegalStateException - if already connected

  See Also:

  • getIfModifiedSince()

• getIfModifiedSince

  public long getIfModifiedSince()

  Returns the value of this object's ifModifiedSince field.

  Returns:

  the value of this object's ifModifiedSince field.

  See Also:

  • setIfModifiedSince(long)

• getDefaultUseCaches

  public boolean getDefaultUseCaches()

  Returns the default value of a URLConnection's useCaches flag.

  This default is "sticky", being a part of the static state of all URLConnections. This flag applies to the next, and all following URLConnections that are created. This default value can be over-ridden per protocol using setDefaultUseCaches(String,boolean)

  Returns:

  the default value of a URLConnection's useCaches flag.

  See Also:

  • setDefaultUseCaches(boolean)

• setDefaultUseCaches

  public void setDefaultUseCaches(boolean defaultusecaches)

  Sets the default value of the useCaches field to the specified value. This default value can be over-ridden per protocol using setDefaultUseCaches(String,boolean)

  Parameters:

  defaultusecaches - the new value.

  See Also:

  • getDefaultUseCaches()

• setDefaultUseCaches

  public static void setDefaultUseCaches(String protocol, boolean defaultVal)

  Sets the default value of the useCaches field for the named protocol to the given value. This value overrides any default setting set by setDefaultUseCaches(boolean) for the given protocol. Successive calls to this method change the setting and affect the default value for all future connections of that protocol. The protocol name is case insensitive.

  Parameters:

  protocol - the protocol to set the default for

  defaultVal - whether caching is enabled by default for the given protocol

  Since:

  9

• getDefaultUseCaches

  public static boolean getDefaultUseCaches(String protocol)

  Returns the default value of the useCaches flag for the given protocol. If setDefaultUseCaches(String,boolean) was called for the given protocol, then that value is returned. Otherwise, if setDefaultUseCaches(boolean) was called, then that value is returned. If neither method was called, the return value is true. The protocol name is case insensitive.

  Parameters:

  protocol - the protocol whose defaultUseCaches setting is required

  Returns:

  the default value of the useCaches flag for the given protocol.

  Since:

  9

• setRequestProperty

  public void setRequestProperty(String key, String value)

  Sets the general request property. If a property with the key already exists, overwrite its value with the new value.

  NOTE: HTTP requires all request properties which can legally have multiple instances with the same key to use a comma-separated list syntax which enables multiple properties to be appended into a single property.

  Parameters:

  key - the keyword by which the request is known (e.g., "Accept").

  value - the value associated with it.

  Throws:

  IllegalStateException - if already connected

  NullPointerException - if key is null

  See Also:

  • getRequestProperty(java.lang.String)

• addRequestProperty

  public void addRequestProperty(String key, String value)

  Adds a general request property specified by a key-value pair. This method will not overwrite existing values associated with the same key.

  Parameters:

  key - the keyword by which the request is known (e.g., "Accept").

  value - the value associated with it.

  Throws:

  IllegalStateException - if already connected

  NullPointerException - if key is null

  Since:

  1.4

  See Also:

  • getRequestProperties()

• getRequestProperty

  public String getRequestProperty(String key)

  Returns the value of the named general request property for this connection.

  Parameters:

  key - the keyword by which the request is known (e.g., "Accept").

  Returns:

  the value of the named general request property for this connection. If key is null, then null is returned.

  Throws:

  IllegalStateException - if already connected

  See Also:

  • setRequestProperty(java.lang.String, java.lang.String)

• getRequestProperties

  public Map<String,List<String>> getRequestProperties()

  Returns an unmodifiable Map of general request properties for this connection. The Map keys are Strings that represent the request-header field names. Each Map value is a unmodifiable List of Strings that represents the corresponding field values.

  Returns:

  a Map of the general request properties for this connection.

  Throws:

  IllegalStateException - if already connected

  Since:

  1.4

• setDefaultRequestProperty

  @Deprecated public static void setDefaultRequestProperty(String key, String value)

  Deprecated.

  The instance specific setRequestProperty method should be used after an appropriate instance of URLConnection is obtained. Invoking this method will have no effect.

  Sets the default value of a general request property. When a URLConnection is created, it is initialized with these properties.

  Parameters:

  key - the keyword by which the request is known (e.g., "Accept").

  value - the value associated with the key.

  See Also:

  • setRequestProperty(java.lang.String,java.lang.String)
  • getDefaultRequestProperty(java.lang.String)

• getDefaultRequestProperty

  @Deprecated public static String getDefaultRequestProperty(String key)

  Deprecated.

  The instance specific getRequestProperty method should be used after an appropriate instance of URLConnection is obtained.

  Returns the value of the default request property. Default request properties are set for every connection.

  Parameters:

  key - the keyword by which the request is known (e.g., "Accept").

  Returns:

  the value of the default request property for the specified key.

  See Also:

  • getRequestProperty(java.lang.String)
  • setDefaultRequestProperty(java.lang.String, java.lang.String)

• setContentHandlerFactory

  public static void setContentHandlerFactory(ContentHandlerFactory fac)

  Sets the ContentHandlerFactory of an application. It can be called at most once by an application.

  The ContentHandlerFactory instance is used to construct a content handler from a content type.

  If there is a security manager, this method first calls the security manager's checkSetFactory method to ensure the operation is allowed. This could result in a SecurityException.

  Parameters:

  fac - the desired factory.

  Throws:

  Error - if the factory has already been defined.

  SecurityException - if a security manager exists and its checkSetFactory method doesn't allow the operation.

  See Also:

  • ContentHandlerFactory
  • getContent()
  • SecurityManager.checkSetFactory()

• guessContentTypeFromName

  public static String guessContentTypeFromName(String fname)

  Tries to determine the content type of an object, based on the specified "file" component of a URL. This is a convenience method that can be used by subclasses that override the getContentType method.

  Parameters:

  fname - a filename.

  Returns:

  a guess as to what the content type of the object is, based upon its file name.

  See Also:

  • getContentType()

• guessContentTypeFromStream

  public static String guessContentTypeFromStream(InputStream is) throws IOException

  Tries to determine the type of an input stream based on the characters at the beginning of the input stream. This method can be used by subclasses that override the getContentType method.

  Ideally, this routine would not be needed. But many http servers return the incorrect content type; in addition, there are many nonstandard extensions. Direct inspection of the bytes to determine the content type is often more accurate than believing the content type claimed by the http server.

  Parameters:

  is - an input stream that supports marks.

  Returns:

  a guess at the content type, or null if none can be determined.

  Throws:

  IOException - if an I/O error occurs while reading the input stream.

  See Also:

  • InputStream.mark(int)
  • InputStream.markSupported()
  • getContentType()