URLConnection (Java Platform SE 7 )

java.lang.Object
- java.net.URLConnection

Direct Known Subclasses:

HttpURLConnection, JarURLConnection
```
public abstract class URLConnection
extends Object
```
The abstract class 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.

---------------------------->
time
1. The connection object is created by invoking the openConnection method on a URL.
2. The setup parameters and general request properties are manipulated.
3. The actual connection to the remote object is made, using the connect method.
4. The remote object becomes available. The header fields and the contents of the remote object can be accessed.
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.
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
- getLastModifed
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 getContent, 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.ietf.org/rfc/rfc2616.txt
 
```
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 and mutator methods getFileNameMap and setFileNameMap are added to access it. This change is also described on the Compatibility page. Invoking the close() methods on the InputStream or OutputStream of an URLConnection after a request may free network resources associated with this instance, unless particular protocol specifications specify different behaviours for it.
Since:

JDK1.0

See Also:
URL.openConnection(), connect(), getContent(), getContentEncoding(), getContentLength(), getContentType(), getDate(), getExpiration(), getHeaderField(int), getHeaderField(java.lang.String), getInputStream(), getLastModified(), getOutputStream(), setAllowUserInteraction(boolean), setDefaultUseCaches(boolean), setDoInput(boolean), setDoOutput(boolean), setIfModifiedSince(long), setRequestProperty(java.lang.String, java.lang.String), setUseCaches(boolean)

`openConnection()`	`connect()`
Manipulate parameters that affect the connection to the remote resource.	Interact with the resource; query header fields and contents.

Field Summary

Fields
Modifier and Type	Field and Description
`protected boolean`	`allowUserInteraction` If `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.
`protected boolean`	`connected` If `false`, this connection object has not created a communications link to the specified URL.
`protected boolean`	`doInput` This variable is set by the `setDoInput` method.
`protected boolean`	`doOutput` This variable is set by the `setDoOutput` method.
`protected long`	`ifModifiedSince` Some protocols support skipping the fetching of the object unless the object has been modified more recently than a certain time.
`protected URL`	`url` The URL represents the remote object on the World Wide Web to which this connection is opened.
`protected boolean`	`useCaches` If `true`, the protocol is allowed to use caching whenever it can.

Constructor Summary

Constructors
Modifier Constructor and Description

protected URLConnection(URL url)
Constructs a URL connection to the specified URL.

Constructors
Modifier	Constructor and Description
`protected`	`URLConnection(URL url)` Constructs a URL connection to the specified URL.

Method Summary

Methods
Modifier and Type	Method and Description
`void`	`addRequestProperty(String key, String value)` Adds a general request property specified by a key-value pair.
`abstract void`	`connect()` Opens a communications link to the resource referenced by this URL, if such a connection has not already been established.
`boolean`	`getAllowUserInteraction()` Returns the value of the `allowUserInteraction` field for this object.
`int`	`getConnectTimeout()` Returns setting for connect timeout.
`Object`	`getContent()` Retrieves the contents of this URL connection.
`Object`	`getContent(Class[] classes)` Retrieves the contents of this URL connection.
`String`	`getContentEncoding()` Returns the value of the `content-encoding` header field.
`int`	`getContentLength()` Returns the value of the `content-length` header field.
`long`	`getContentLengthLong()` Returns the value of the `content-length` header field as a long.
`String`	`getContentType()` Returns the value of the `content-type` header field.
`long`	`getDate()` Returns the value of the `date` header field.
`static boolean`	`getDefaultAllowUserInteraction()` Returns the default value of the `allowUserInteraction` field.
`static String`	`getDefaultRequestProperty(String key)` Deprecated. The instance specific getRequestProperty method should be used after an appropriate instance of URLConnection is obtained.
`boolean`	`getDefaultUseCaches()` Returns the default value of a `URLConnection`'s `useCaches` flag.
`boolean`	`getDoInput()` Returns the value of this `URLConnection`'s `doInput` flag.
`boolean`	`getDoOutput()` Returns the value of this `URLConnection`'s `doOutput` flag.
`long`	`getExpiration()` Returns the value of the `expires` header field.
`static FileNameMap`	`getFileNameMap()` Loads filename map (a mimetable) from a data file.
`String`	`getHeaderField(int n)` Returns the value for the `n`^th header field.
`String`	`getHeaderField(String name)` Returns the value of the named header field.
`long`	`getHeaderFieldDate(String name, long Default)` Returns the value of the named field parsed as date.
`int`	`getHeaderFieldInt(String name, int Default)` Returns the value of the named field parsed as a number.
`String`	`getHeaderFieldKey(int n)` Returns the key for the `n`^th header field.
`long`	`getHeaderFieldLong(String name, long Default)` Returns the value of the named field parsed as a number.
`Map<String,List<String>>`	`getHeaderFields()` Returns an unmodifiable Map of the header fields.
`long`	`getIfModifiedSince()` Returns the value of this object's `ifModifiedSince` field.
`InputStream`	`getInputStream()` Returns an input stream that reads from this open connection.
`long`	`getLastModified()` Returns the value of the `last-modified` header field.
`OutputStream`	`getOutputStream()` Returns an output stream that writes to this connection.
`Permission`	`getPermission()` Returns a permission object representing the permission necessary to make the connection represented by this object.
`int`	`getReadTimeout()` Returns setting for read timeout.
`Map<String,List<String>>`	`getRequestProperties()` Returns an unmodifiable Map of general request properties for this connection.
`String`	`getRequestProperty(String key)` Returns the value of the named general request property for this connection.
`URL`	`getURL()` Returns the value of this `URLConnection`'s `URL` field.
`boolean`	`getUseCaches()` Returns the value of this `URLConnection`'s `useCaches` field.
`static String`	`guessContentTypeFromName(String fname)` Tries to determine the content type of an object, based on the specified "file" component of a URL.
`static String`	`guessContentTypeFromStream(InputStream is)` Tries to determine the type of an input stream based on the characters at the beginning of the input stream.
`void`	`setAllowUserInteraction(boolean allowuserinteraction)` Set the value of the `allowUserInteraction` field of this `URLConnection`.
`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.
`static void`	`setContentHandlerFactory(ContentHandlerFactory fac)` Sets the `ContentHandlerFactory` of an application.
`static void`	`setDefaultAllowUserInteraction(boolean defaultallowuserinteraction)` Sets the default value of the `allowUserInteraction` field for all future `URLConnection` objects to the specified value.
`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.
`void`	`setDefaultUseCaches(boolean defaultusecaches)` Sets the default value of the `useCaches` field to the specified value.
`void`	`setDoInput(boolean doinput)` Sets the value of the `doInput` field for this `URLConnection` to the specified value.
`void`	`setDoOutput(boolean dooutput)` Sets the value of the `doOutput` field for this `URLConnection` to the specified value.
`static void`	`setFileNameMap(FileNameMap map)` Sets the FileNameMap.
`void`	`setIfModifiedSince(long ifmodifiedsince)` Sets the value of the `ifModifiedSince` field of this `URLConnection` to the specified value.
`void`	`setReadTimeout(int timeout)` Sets the read timeout to a specified timeout, in milliseconds.
`void`	`setRequestProperty(String key, String value)` Sets the general request property.
`void`	`setUseCaches(boolean usecaches)` Sets the value of the `useCaches` field of this `URLConnection` to the specified value.
`String`	`toString()` Returns a `String` representation of this URL connection.

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

- Field Detail
  - url
```
protected URL url
```
    The URL represents the remote object on the World Wide Web to which this connection is opened.
    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.
    
    See Also:
    getURL(), url
  - doInput
```
protected boolean doInput
```
    This variable is set by the 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.
    
    See Also:
    getDoInput(), setDoInput(boolean)
  - doOutput
```
protected boolean doOutput
```
    This variable is set by the setDoOutput method. Its value is returned by the getDoOutput 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.
    
    See Also:
    getDoOutput(), setDoOutput(boolean)
  - allowUserInteraction
```
protected boolean allowUserInteraction
```
    If 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.
    
    See Also:
    getAllowUserInteraction(), setAllowUserInteraction(boolean), setDefaultAllowUserInteraction(boolean)
  - useCaches
```
protected boolean useCaches
```
    If 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.
    
    See Also:
    setUseCaches(boolean), getUseCaches(), setDefaultUseCaches(boolean)
  - ifModifiedSince
```
protected long ifModifiedSince
```
    Some protocols support skipping the fetching of the object unless the object has been modified more recently than a certain time.
    A nonzero value gives a time as the number of milliseconds 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.
    
    See Also:
    getIfModifiedSince(), setIfModifiedSince(long)
  - connected
```
protected boolean connected
```
    If false, this connection object has not created a communications link to the specified URL. If true, the communications link has been established.
- Constructor Detail
  - URLConnection
```
protected URLConnection(URL url)
```
    Constructs a URL connection to the specified URL. A connection to the object referenced by the URL is not created.
    
    Parameters:
    url - the specified URL.
- Method Detail
  - 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 at lib/content-types.properties under java home.
    
    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 implmentation 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:
    
    7.0
  - 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:
    
    7.0
  - 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. 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.
  - getHeaderField
```
public String getHeaderField(int n)
```
    Returns the value for the n^th header field. It returns null if there are fewer than n+1fields.
    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:
    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 content handler factory has yet been set up, or if the factory's createContentHandler method returns null, then the application loads the class named:
      sun.net.www.content.<contentType>
      where <contentType> is formed by taking the content-type string, replacing all slash characters with a 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.
    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 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 obtaine

Class URLConnection

Field Summary

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Field Detail

url

doInput

doOutput

allowUserInteraction

useCaches

ifModifiedSince

connected

Constructor Detail

URLConnection

Method Detail

getFileNameMap

setFileNameMap

connect

setConnectTimeout

getConnectTimeout

setReadTimeout

getReadTimeout

getURL

getContentLength

getContentLengthLong

getContentType

getContentEncoding

getExpiration

getDate

getLastModified

getHeaderField

getHeaderFields

getHeaderFieldInt

getHeaderFieldLong

getHeaderFieldDate

getHeaderFieldKey

getHeaderField

getContent

getContent

getPermission