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java.lang.Object | +----java.net.URLConnection
URLConnection is the superclass of all classes that represent a communications link between the application and a URL. Instances of this class can be used both to read from and to write to the resource referenced by the URL. In general, creating a connection to a URL is a multistep process: openConnection() | connect() |
|---|---|
| Manipulate parameters that affect the connection to the remote resource. | Interact with the resource; query header fields and contents. |
openConnection method on a URL. connect method. The setup parameters are modified using the following methods:
- setAllowUserInteraction
- setDoInput
- setDoOutput
- setIfModifiedSince
- setUseCaches
and the general request properties are modified using the method:
- setRequestProperty
Default values for the AllowUserInteraction and UseCaches parameters can be set using the methods setDefaultAllowUserInteraction and setDefaultUseCaches. Default values for general request properties can be set using the setDefaultRequestProperty method.
Each of the above set methods has a corresponding get method to retrieve the value of the parameter or general request property. The specific parameters and general request properties that are applicable are protocol specific.
The following methods are used to access the header fields and the contents after the connection is made to the remote object:
- getContent
- getHeaderField
- getInputStream
- getOutputStream
Certain header fields are accessed frequently. The methods:
- getContentEncoding
- getContentLength
- getContentType
- getDate
- getExpiration
- getLastModified
provide convenient access to these fields. The getContentType method is used by the getContent method to determine the type of the remote object; subclasses may find it convenient to override the getContentType method.
In the common case, all of the pre-connection parameters and general request properties can be ignored: the pre-connection parameters and request properties default to sensible values. For most clients of this interface, there are only two interesting methods: getInputStream and getObject, which are mirrored in the URL class by convenience methods.
More information on the request properties and header fields of an http connection can be found at:
http://www.w3.org/hypertext/WWW/Protocols/HTTP1.0/draft-ietf-http-spec.html Note about fileNameMap: In versions prior to JDK 1.1.6, field fileNameMap of URLConnection was public. In JDK 1.1.6 and later, fileNameMap is private; accessor method getFileNameMap() and mutator method setFileNameMap(FileNameMap) are added to access it. This change is also described on the JDK 1.1.x Compatibility page.
allowUserInteraction true, this URL is being examined in a context in which it makes sense to allow user interactions such as popping up an authentication dialog. connected false, this connection object has not created a communications link to the specified URL. doInput setDoInput method. doOutput setDoOutput method. ifModifiedSince url useCaches true, the protocol is allowed to use caching whenever it can. 
URLConnection(URL) 
connect() getAllowUserInteraction() allowUserInteraction field for this object. getContent() getContentEncoding() content-encoding header field. getContentLength() content-length header field. getContentType() content-type header field. getDate() date header field. 
getDefaultAllowUserInteraction() allowUserInteraction field. getDefaultRequestProperty(String) getDefaultUseCaches() URLConnection's useCaches flag. getDoInput() URLConnection's doInput flag. getDoOutput() URLConnection's doOutput flag. getExpiration() expires header field. getFileNameMap() getHeaderField(int) nth header field. getHeaderField(String) getHeaderFieldDate(String, long) getHeaderFieldInt(String, int) getHeaderFieldKey(int) nth header field. getIfModifiedSince() ifModifiedSince field. getInputStream() getLastModified() last-modified header field. getOutputStream() getRequestProperty(String) getURL() URLConnection's URL field. getUseCaches() URLConnection's useCaches field. guessContentTypeFromName(String) guessContentTypeFromStream(InputStream) setAllowUserInteraction(boolean) allowUserInteraction field of this URLConnection. setContentHandlerFactory(ContentHandlerFactory) ContentHandlerFactory of an application. setDefaultAllowUserInteraction(boolean) allowUserInteraction field for all future URLConnection objects to the specified value. setDefaultRequestProperty(String, String) setDefaultUseCaches(boolean) useCaches field to the specified value. setDoInput(boolean) doInput field for this URLConnection to the specified value. setDoOutput(boolean) doOutput field for this URLConnection to the specified value. setFileNameMap(FileNameMap) setIfModifiedSince(long) ifModifiedSince field of this URLConnection to the specified value. setRequestProperty(String, String) setUseCaches(boolean) useCaches field of this URLConnection to the specified value. toString() String representation of this URL connection. 
url
protected URL url
The value of this field can be accessed by the getURL method.
The default value of this variable is the value of the URL argument in the URLConnection constructor.
doInput
protected boolean doInput
setDoInput method. Its value is returned by the getDoInput method. A URL connection can be used for input and/or output. Setting the doInput flag to true indicates that the application intends to read data from the URL connection.
The default value of this field is true.
doOutput
protected boolean doOutput
setDoOutput method. Its value is returned by the getDoInput method. A URL connection can be used for input and/or output. Setting the doOutput flag to true indicates that the application intends to write data to the URL connection.
The default value of this field is false.
allowUserInteraction
protected boolean allowUserInteraction
true, this URL is being examined in a context in which it makes sense to allow user interactions such as popping up an authentication dialog. If false, then no user interaction is allowed. The value of this field can be set by the setAllowUserInteraction method. Its value is returned by the getAllowUserInteraction method. Its default value is the value of the argument in the last invocation of the setDefaultAllowUserInteraction method.
useCaches
protected boolean useCaches
true, the protocol is allowed to use caching whenever it can. If false, the protocol must always try to get a fresh copy of the object. This field is set by the setUseCaches method. Its value is returned by the getUseCaches method.
Its default value is the value given in the last invocation of the setDefaultUseCaches method.
ifModifiedSince
protected long ifModifiedSince
A nonzero value gives a time as the number of seconds since January 1, 1970, GMT. The object is fetched only if it has been modified more recently than that time.
This variable is set by the setIfModifiedSince method. Its value is returned by the getIfModifiedSince method.
The default value of this field is 0, indicating that the fetching must always occur.
connected
protected boolean connected
false, this connection object has not created a communications link to the specified URL. If true, the communications link has been established.
URLConnection
protected URLConnection(URL url)
getFileNameMap
public static FileNameMap getFileNameMap()
setFileNameMap
public static void setFileNameMap(FileNameMap map)
connect
public abstract void connect() throws IOException
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.
getURL
public URL getURL()
URLConnection's URL field. URLConnection's URL field. getContentLength
public int getContentLength()
content-length header field. -1 if the content length is not known. getContentType
public String getContentType()
content-type header field. null if not known. getContentEncoding
public String getContentEncoding()
content-encoding header field. null if not known. getExpiration
public long getExpiration()
expires header field. getDate
public long getDate()
date header field. 0 if not known. The value returned is the number of seconds since January 1, 1970 GMT. getLastModified
public long getLastModified()
last-modified header field. The result is the number of seconds since January 1, 1970 GMT. URLConnection was last modified, or 0 if not known. getHeaderField
public String getHeaderField(String name)
null if there is no such field in the header. getHeaderFieldInt
public int getHeaderFieldInt(String name,
int Default)
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.
Default value is returned if the field is missing or malformed. getHeaderFieldDate
public long getHeaderFieldDate(String name,
long Default)
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.
Default argument is returned if the field is missing or malformed. getHeaderFieldKey
public String getHeaderFieldKey(int n)
nth header field. nth header field, or null if there are fewer than n fields. getHeaderField
public String getHeaderField(int n)
nth header field. It returns null if there are fewer than n fields. This method can be used in conjunction with the getHeaderFieldKey method to iterate through all the headers in the message.
nth header field. getContent
public Object getContent() throws IOException
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:
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. createContentHandler method returns null, then the application loads the class named: sun.net.www.content.<contentType> period ('.'), and all other non-alphanumeric characters with the underscore character '_'. The alphanumeric characters are specifically the 26 uppercase ASCII letters 'A' through 'Z', the 26 lowercase ASCII letters 'a' through 'z', and the 10 ASCII digits '0' through '9'. If the specified class does not exist, or is not a subclass of ContentHandler, then an UnknownServiceException is thrown. instanceOf operation should be used to determine the specific kind of object returned. getInputStream
public InputStream getInputStream() throws IOException
getOutputStream
public OutputStream getOutputStream() throws IOException
toString
public String toString()
String representation of this URL connection. URLConnection. setDoInput
public void setDoInput(boolean doinput)
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 unless DoOutput is explicitly set to true, in which case DoInput defaults to false.
getDoInput
public boolean getDoInput()
URLConnection's doInput flag. URLConnection's doInput flag. setDoOutput
public void setDoOutput(boolean dooutput)
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.
getDoOutput
public boolean getDoOutput()
URLConnection's doOutput flag. URLConnection's doOutput flag. setAllowUserInteraction
public void setAllowUserInteraction(boolean allowuserinteraction)
allowUserInteraction field of this URLConnection. getAllowUserInteraction
public boolean getAllowUserInteraction()
allowUserInteraction field for this object. allowUserInteraction field for this object. setDefaultAllowUserInteraction
public static void setDefaultAllowUserInteraction(boolean defaultallowuserinteraction)
allowUserInteraction field for all future URLConnection objects to the specified value. getDefaultAllowUserInteraction
public static boolean getDefaultAllowUserInteraction()
allowUserInteraction field. Ths 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.
allowUserInteraction field. setUseCaches
public void setUseCaches(boolean usecaches)
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.
getUseCaches
public boolean getUseCaches()
URLConnection's useCaches field. URLConnection's useCaches field. setIfModifiedSince
public void setIfModifiedSince(long ifmodifiedsince)
ifModifiedSince field of this URLConnection to the specified value. getIfModifiedSince
public long getIfModifiedSince()
ifModifiedSince field. ifModifiedSince field. getDefaultUseCaches
public boolean getDefaultUseCaches()
URLConnection's useCaches flag. Ths 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.
URLConnection's useCaches flag. setDefaultUseCaches
public void setDefaultUseCaches(boolean defaultusecaches)
useCaches field to the specified value. setRequestProperty
public void setRequestProperty(String key, String value)
accept"). getRequestProperty
public String getRequestProperty(String key)
setDefaultRequestProperty
public static void setDefaultRequestProperty(String key, String value)
URLConnection is created, it is initialized with these properties. accept"). getDefaultRequestProperty
public static String getDefaultRequestProperty(String key)
setContentHandlerFactory
public static synchronized void setContentHandlerFactory(ContentHandlerFactory fac)
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
guessContentTypeFromName
protected static String guessContentTypeFromName(String fname)
getContentType method. guessContentTypeFromStream
public static String guessContentTypeFromStream(InputStream is) throws IOException
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.
null if none can be determined. All Packages Class Hierarchy This Package Previous Next Index