java.lang.Object java.net.URLConnection
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() |
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Manipulate parameters that affect the connection to the remote resource. | Interact with the resource; query header fields and contents. |
The setup parameters are modified using the following methods:
and the general request properties are modified using the method:
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:
Certain header fields are accessed frequently. The methods:
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:
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. Invokinghttp://www.ietf.org/rfc/rfc2068.txt
Field Summary | |
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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 | |
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protected |
URLConnection
(
URL
url) Constructs a URL connection to the specified URL. |
Method Summary | |
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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. |
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. |
Map |
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 |
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
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. |
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 |
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clone , equals , finalize , getClass , hashCode , notify , notifyAll , wait , wait , wait |
Field Detail |
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protected URL url
The value of this field can be accessed by the getURL method.
The default value of this variable is the value of the URL argument in the URLConnection constructor.
protected boolean doInput
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.
protected boolean doOutput
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.
protected boolean allowUserInteraction
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.
protected boolean useCaches
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.
protected long ifModifiedSince
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.
protected boolean connected
Constructor Detail |
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protected URLConnection(URL url)
Method Detail |
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public static FileNameMap getFileNameMap()
public static void setFileNameMap(FileNameMap map)
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.
public abstract void connect() throws IOException
If the connect method is called when the connection has already been opened (indicated by the connected field having the value true), the call is ignored.
URLConnection objects go through two phases: first they are created, then they are connected. After being created, and before being connected, various options can be specified (e.g., doInput and UseCaches). After connecting, it is an error to try to set them. Operations that depend on being connected, like getContentLength, will implicitly perform the connection, if necessary.
public void setConnectTimeout (int timeout)
Some non-standard implmentation of this method may ignore the specified timeout. To see the connect timeout set, please call getConnectTimeout().
public int getConnectTimeout ()
0 return implies that the option is disabled (i.e., timeout of infinity).
public void setReadTimeout (int timeout)
Some non-standard implementation of this method ignores the specified timeout. To see the read timeout set, please call getReadTimeout().
public int getReadTimeout ()
public URL getURL()
public int getContentLength()
public String getContentType()
public String getContentEncoding()
public long getExpiration()
public long getDate()
public long getLastModified()
public String getHeaderField(String name)
If called on a connection that sets the same header multiple times with possibly different values, only the last value is returned.
public Map getHeaderFields()
public int getHeaderFieldInt(String name, int Default)
This form of getHeaderField exists because some connection types (e.g., http-ng) have pre-parsed headers. Classes for that connection type can override this method and short-circuit the parsing.
public long getHeaderFieldDate(String name, long Default)
This form of getHeaderField exists because some connection types (e.g., http-ng) have pre-parsed headers. Classes for that connection type can override this method and short-circuit the parsing.
public String getHeaderFieldKey(int n)
public String getHeaderField(int n)
This method can be used in conjunction with the getHeaderFieldKey method to iterate through all the headers in the message.
public Object getContent() throws IOException
This method first determines the content type of the object by calling the getContentType method. If this is the first time that the application has seen that specific content type, a content handler for that content type is created:
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.sun.net.www.content.<contentType>
public Object getContent(Class[] classes) throws IOException
public Permission getPermission() throws IOException
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.
public InputStream getInputStream() throws IOException
public OutputStream getOutputStream() throws IOException
public String toString()
public void setDoInput(boolean doinput)
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.
public boolean getDoInput()
public void setDoOutput(boolean dooutput)
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.
public boolean getDoOutput()
public void setAllowUserInteraction(boolean allowuserinteraction)
public boolean getAllowUserInteraction()
public static void setDefaultAllowUserInteraction(boolean defaultallowuserinteraction)
public static boolean getDefaultAllowUserInteraction()
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.
public void setUseCaches(boolean usecaches)
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.
public boolean getUseCaches()
public void setIfModifiedSince(long ifmodifiedsince)
public long getIfModifiedSince()
public boolean getDefaultUseCaches()
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.
public void setDefaultUseCaches(boolean defaultusecaches)
public void setRequestProperty(String key, String value)
NOTE: HTTP requires all request properties which can legally have multiple instances with the same key to use a comma-seperated list syntax which enables multiple properties to be appended into a single property.
public void addRequestProperty(String key, String value)
public String getRequestProperty(String key)
public Map getRequestProperties()
public static void setDefaultRequestProperty(String key, String value)
public static String getDefaultRequestProperty(String key)
public static void setContentHandlerFactory(ContentHandlerFactory fac)
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.
public static String guessContentTypeFromName(String fname)
public static String guessContentTypeFromStream(InputStream is) throws IOException
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.