java.net

Class URLConnection

java.lang.Object

java.net.URLConnection

Direct Known Subclasses:

HttpURLConnection

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
 

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

Author:

James Gosling

See Also:

URL.openConnection(), connect(), getContent(), getContentEncoding(), getContentLength(), getContentType(), getHeaderField(int), getHeaderField(java.lang.String), getInputStream(), getOutputStream(), setAllowUserInteraction(boolean), setDefaultUseCaches(boolean), setDoInput(boolean), setDoOutput(boolean), setRequestProperty(java.lang.String, java.lang.String), setUseCaches(boolean)

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 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.

Method Summary

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.
static boolean	getDefaultAllowUserInteraction() Returns the default value of the allowUserInteraction field.
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.
String	getHeaderField(int n) Returns the value for the nth header field.
String	getHeaderField(String name) Returns the value of the named header field.
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 nth 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.
InputStream	getInputStream() Returns an input stream that reads from this open connection.
OutputStream	getOutputStream() Returns an output stream that writes to this connection.
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.
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.
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.
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, getClass, hashCode, notify, notifyAll, wait, wait, wait

Field Detail

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)

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.

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)

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

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)

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

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()

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:

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

See Also:

connected, getConnectTimeout(), setConnectTimeout(int)

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)

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()

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

@Nullable
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)

getContentEncoding

@Nullable
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)

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

@Nullable
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)

getDefaultAllowUserInteraction

public static boolean getDefaultAllowUserInteraction()

Returns the default value of the 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.

Returns:

the default value of the allowUserInteraction field.

See Also:

setDefaultAllowUserInteraction(boolean)

getDefaultUseCaches

public boolean getDefaultUseCaches()

Returns the default value of a 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.

Returns:

the default value of a URLConnection's useCaches flag.

See Also:

setDefaultUseCaches(boolean)

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)

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)

getHeaderField

@Nullable
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)

getHeaderField

@Nullable
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.

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.

getHeaderFieldKey

@Nullable
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.

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

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

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.

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()

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

getRequestProperty

@Nullable
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)

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

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)

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()

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()

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()

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()

setDefaultUseCaches

public void setDefaultUseCaches(boolean defaultusecaches)

Sets the default value of the useCaches field to the specified value.

Parameters:

defaultusecaches - the new value.

See Also:

getDefaultUseCaches()

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()

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()

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()

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)

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.

Parameters:

usecaches - a boolean indicating whether or not to allow caching

Throws:

IllegalStateException - if already connected

See Also:

getUseCaches()

toString

public String toString()

Returns a String representation of this URL connection.

Overrides:

toString in class Object

Returns:

a string representation of this URLConnection.