Class 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:

  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
  • 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 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:
1.0
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)

Field Summary

Fields
Modifier and Type Field 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 Description
protected URLConnection​(URL url)

Constructs a URL connection to the specified URL.

Method Summary

All Methods Static Methods Instance Methods Abstract Methods Concrete Methods Deprecated Methods
Modifier and Type Method 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.
static boolean getDefaultUseCaches​(String protocol)

Returns the default value of the useCaches flag for the given protocol.
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 nth 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 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.
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. 0 return implies that the option is disabled (i.e., timeout of infinity).
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.
void setDefaultUseCaches​(boolean defaultusecaches)

Sets the default value of the useCaches field to the specified value.
static void setDefaultUseCaches​(String protocol, boolean defaultVal)

Sets the default value of the useCaches field for the named protocol to the given 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 declared in 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.

The default setting may be overridden per protocol with setDefaultUseCaches(String,boolean).

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.

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 nth 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 nth header field, or null if there are fewer than n+1 fields.

getHeaderField

public String getHeaderField​(int n)

Returns the value for the nth 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 nth 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()