java.net.URLConnection Maven / Gradle / Ivy
/*
This is not an official specification document, and usage is restricted.
NOTICE
(c) 2005-2007 Sun Microsystems, Inc. All Rights Reserved.
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Any work generated from this file, such as unified javadocs or compiled
stub files, must be accompanied by this notice in its entirety.
This work corresponds to the API signatures of JSR 219: Foundation
Profile 1.1. In the event of a discrepency between this work and the
JSR 219 specification, which is available at
http://www.jcp.org/en/jsr/detail?id=219, the latter takes precedence.
*/
package java.net;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.Hashtable;
import java.text.DateFormat;
import java.util.StringTokenizer;
import java.util.Collections;
import java.util.Map;
import java.security.Permission;
import java.security.AccessController;
/**
* 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
* - The connection object is created by invoking the
*
openConnection method on a URL.
* - The setup parameters and general request properties are manipulated.
*
- The actual connection to the remote object is made, using the
*
connect method.
* - 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/rfc2068.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 {@link #getFileNameMap() getFileNameMap} and
* {@link #setFileNameMap(java.net.FileNameMap) setFileNameMap} are added
* to access it. This change is also described on the
* Compatibility page.
*
* Calling 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.
*
* @author James Gosling
* @version 1.75, 05/03/00
* @see java.net.URL#openConnection()
* @see java.net.URLConnection#connect()
* @see java.net.URLConnection#getContent()
* @see java.net.URLConnection#getContentEncoding()
* @see java.net.URLConnection#getContentLength()
* @see java.net.URLConnection#getContentType()
* @see java.net.URLConnection#getDate()
* @see java.net.URLConnection#getExpiration()
* @see java.net.URLConnection#getHeaderField(int)
* @see java.net.URLConnection#getHeaderField(java.lang.String)
* @see java.net.URLConnection#getInputStream()
* @see java.net.URLConnection#getLastModified()
* @see java.net.URLConnection#getOutputStream()
* @see java.net.URLConnection#setAllowUserInteraction(boolean)
* @see java.net.URLConnection#setDefaultUseCaches(boolean)
* @see java.net.URLConnection#setDoInput(boolean)
* @see java.net.URLConnection#setDoOutput(boolean)
* @see java.net.URLConnection#setIfModifiedSince(long)
* @see java.net.URLConnection#setRequestProperty(java.lang.String, java.lang.String)
* @see java.net.URLConnection#setUseCaches(boolean)
* @since JDK1.0
*/
public abstract class URLConnection
{
/**
* 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 java.net.URLConnection#getURL()
* @see java.net.URLConnection#url
*/
protected URL url;
/**
* 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 java.net.URLConnection#getDoInput()
* @see java.net.URLConnection#setDoInput(boolean)
*/
protected boolean doInput;
/**
* 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 java.net.URLConnection#getDoOutput()
* @see java.net.URLConnection#setDoOutput(boolean)
*/
protected boolean doOutput;
/**
* 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 java.net.URLConnection#getAllowUserInteraction()
* @see java.net.URLConnection#setAllowUserInteraction(boolean)
* @see java.net.URLConnection#setDefaultAllowUserInteraction(boolean)
*/
protected boolean allowUserInteraction;
/**
* 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 java.net.URLConnection#setUseCaches(boolean)
* @see java.net.URLConnection#getUseCaches()
* @see java.net.URLConnection#setDefaultUseCaches(boolean)
*/
protected boolean useCaches;
/**
* 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 java.net.URLConnection#getIfModifiedSince()
* @see java.net.URLConnection#setIfModifiedSince(long)
*/
protected long ifModifiedSince;
/**
* If false, this connection object has not created a
* communications link to the specified URL. If true,
* the communications link has been established.
*/
protected boolean connected;
/**
* Constructs a URL connection to the specified URL. A connection to
* the object referenced by the URL is not created.
*
* @param url the specified URL.
*/
protected URLConnection(URL url) { }
/**
* 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.
*
* @return the FileNameMap
* @since 1.2
* @see #setFileNameMap(java.net.FileNameMap)
*/
public static synchronized FileNameMap getFileNameMap() {
return null;
}
/**
* 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.
*
* @param map the FileNameMap to be set
* @exception SecurityException if a security manager exists and its
* checkSetFactory method doesn't allow the operation.
* @see SecurityManager#checkSetFactory
* @see #getFileNameMap()
* @since 1.2
*/
public static void setFileNameMap(FileNameMap map) { }
/**
* 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.
*
* @exception IOException if an I/O error occurs while opening the
* connection.
* @see java.net.URLConnection#connected
*/
public abstract void connect() throws IOException;
/**
* Returns the value of this URLConnection's URL
* field.
*
* @return the value of this URLConnection's URL
* field.
* @see java.net.URLConnection#url
*/
public URL getURL() {
return null;
}
/**
* Returns the value of the content-length header field.
*
* @return the content length of the resource that this connection's URL
* references, or -1 if the content length is
* not known.
*/
public int getContentLength() {
return 0;
}
/**
* Returns the value of the content-type header field.
*
* @return the content type of the resource that the URL references,
* or null if not known.
* @see java.net.URLConnection#getHeaderField(java.lang.String)
*/
public String getContentType() {
return null;
}
/**
* Returns the value of the content-encoding header field.
*
* @return the content encoding of the resource that the URL references,
* or null if not known.
* @see java.net.URLConnection#getHeaderField(java.lang.String)
*/
public String getContentEncoding() {
return null;
}
/**
* Returns the value of the expires header field.
*
* @return 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 java.net.URLConnection#getHeaderField(java.lang.String)
*/
public long getExpiration() {
return -1;
}
/**
* Returns the value of the date header field.
*
* @return 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 java.net.URLConnection#getHeaderField(java.lang.String)
*/
public long getDate() {
return -1;
}
/**
* Returns the value of the last-modified header field.
* The result is the number of milliseconds since January 1, 1970 GMT.
*
* @return the date the resource referenced by this
* URLConnection was last modified, or 0 if not known.
* @see java.net.URLConnection#getHeaderField(java.lang.String)
*/
public long getLastModified() {
return -1;
}
/**
* 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.
*
*
* @param name the name of a header field.
* @return the value of the named header field, or null
* if there is no such field in the header.
*/
public String getHeaderField(String name) {
return null;
}
/**
* 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.
*
* @return a Map of header fields
* @since 1.4
*/
public Map getHeaderFields() {
return null;
}
/**
* 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.
*
* @param name the name of the header field.
* @param Default the default value.
* @return the value of the named field, parsed as an integer. The
* Default value is returned if the field is
* missing or malformed.
*/
public int getHeaderFieldInt(String name, int Default) {
return 0;
}
/**
* 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.
*
* @param name the name of the header field.
* @param Default a default value.
* @return the value of the field, parsed as a date. The value of the
* Default argument is returned if the field is
* missing or malformed.
*/
public long getHeaderFieldDate(String name, long Default) {
return -1;
}
/**
* Returns the key for the nth header field.
* It returns null if there are fewer than n+1 fields.
*
* @param n an index, where n>=0
* @return the key for the nth header field,
* or null if there are fewer than n+1
* fields.
*/
public String getHeaderFieldKey(int n) {
return null;
}
/**
* 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
* {@link #getHeaderFieldKey(int) getHeaderFieldKey} method to iterate through all
* the headers in the message.
*
* @param n an index, where n>=0
* @return the value of the nth header field
* or null if there are fewer than n+1 fields
* @see java.net.URLConnection#getHeaderFieldKey(int)
*/
public String getHeaderField(int n) {
return null;
}
/**
* 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:
*
* - 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.
* - 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.
*
*
* @return the object fetched. The instanceof operator
* should be used to determine the specific kind of object
* returned.
* @exception IOException if an I/O error occurs while
* getting the content.
* @exception UnknownServiceException if the protocol does not support
* the content type.
* @see java.net.ContentHandlerFactory#createContentHandler(java.lang.String)
* @see java.net.URLConnection#getContentType()
* @see java.net.URLConnection#setContentHandlerFactory(java.net.ContentHandlerFactory)
*/
public Object getContent() throws IOException {
return null;
}
/**
* Retrieves the contents of this URL connection.
*
* @param classes the Class array
* indicating the requested types
* @return 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.
* @exception IOException if an I/O error occurs while
* getting the content.
* @exception UnknownServiceException if the protocol does not support
* the content type.
* @see java.net.URLConnection#getContent()
* @see java.net.ContentHandlerFactory#createContentHandler(java.lang.String)
* @see java.net.URLConnection#getContent(java.lang.Class[])
* @see java.net.URLConnection#setContentHandlerFactory(java.net.ContentHandlerFactory)
*/
public Object getContent(Class[] classes) throws IOException {
return null;
}
/**
* 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 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.
*
* @return the permission object representing the permission
* necessary to make the connection represented by this
* URLConnection.
*
* @exception IOException if the computation of the permission
* requires network or file I/O and an exception occurs while
* computing it.
*/
public Permission getPermission() throws IOException {
return null;
}
/**
* Returns an input stream that reads from this open connection.
*
* @return an input stream that reads from this open connection.
* @exception IOException if an I/O error occurs while
* creating the input stream.
* @exception UnknownServiceException if the protocol does not support
* input.
*/
public InputStream getInputStream() throws IOException {
return null;
}
/**
* Returns an output stream that writes to this connection.
*
* @return an output stream that writes to this connection.
* @exception IOException if an I/O error occurs while
* creating the output stream.
* @exception UnknownServiceException if the protocol does not support
* output.
*/
public OutputStream getOutputStream() throws IOException {
return null;
}
/**
* Returns a String representation of this URL connection.
*
* @return a string representation of this URLConnection.
*/
public String toString() {
return null;
}
/**
* 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.
*
* @param doinput the new value.
* @throws IllegalStateException if already connected
* @see java.net.URLConnection#doInput
* @see #getDoInput()
*/
public void setDoInput(boolean doinput) { }
/**
* Returns the value of this URLConnection's
* doInput flag.
*
* @return the value of this URLConnection's
* doInput flag.
* @see #setDoInput(boolean)
*/
public boolean getDoInput() {
return false;
}
/**
* 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.
*
* @param dooutput the new value.
* @throws IllegalStateException if already connected
* @see #getDoOutput()
*/
public void setDoOutput(boolean dooutput) { }
/**
* Returns the value of this URLConnection's
* doOutput flag.
*
* @return the value of this URLConnection's
* doOutput flag.
* @see #setDoOutput(boolean)
*/
public boolean getDoOutput() {
return false;
}
/**
* Set the value of the allowUserInteraction field of
* this URLConnection.
*
* @param allowuserinteraction the new value.
* @throws IllegalStateException if already connected
* @see #getAllowUserInteraction()
*/
public void setAllowUserInteraction(boolean allowuserinteraction) { }
/**
* Returns the value of the allowUserInteraction field for
* this object.
*
* @return the value of the allowUserInteraction field for
* this object.
* @see #setAllowUserInteraction(boolean)
*/
public boolean getAllowUserInteraction() {
return false;
}
/**
* Sets the default value of the
* allowUserInteraction field for all future
* URLConnection objects to the specified value.
*
* @param defaultallowuserinteraction the new value.
* @see #getDefaultAllowUserInteraction()
*/
public static void setDefaultAllowUserInteraction(boolean
defaultallowuserinteraction)
{ }
/**
* 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.
*
* @return the default value of the allowUserInteraction
* field.
* @see #setDefaultAllowUserInteraction(boolean)
*/
public static boolean getDefaultAllowUserInteraction() {
return false;
}
/**
* 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.
*
* @param usecaches a boolean indicating whether
* or not to allow caching
* @throws IllegalStateException if already connected
* @see #getUseCaches()
*/
public void setUseCaches(boolean usecaches) { }
/**
* Returns the value of this URLConnection's
* useCaches field.
*
* @return the value of this URLConnection's
* useCaches field.
* @see #setUseCaches(boolean)
*/
public boolean getUseCaches() {
return false;
}
/**
* Sets the value of the ifModifiedSince field of
* this URLConnection to the specified value.
*
* @param ifmodifiedsince the new value.
* @throws IllegalStateException if already connected
* @see #getIfModifiedSince()
*/
public void setIfModifiedSince(long ifmodifiedsince) { }
/**
* Returns the value of this object's ifModifiedSince field.
*
* @return the value of this object's ifModifiedSince field.
* @see #setIfModifiedSince(long)
*/
public long getIfModifiedSince() {
return -1;
}
/**
* 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.
*
* @return the default value of a URLConnection's
* useCaches flag.
* @see #setDefaultUseCaches(boolean)
*/
public boolean getDefaultUseCaches() {
return false;
}
/**
* Sets the default value of the useCaches field to the
* specified value.
*
* @param defaultusecaches the new value.
* @see #getDefaultUseCaches()
*/
public void setDefaultUseCaches(boolean defaultusecaches) { }
/**
* 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-seperated list syntax which enables multiple
* properties to be appended into a single property.
*
* @param key the keyword by which the request is known
* (e.g., "accept").
* @param value the value associated with it.
* @throws IllegalStateException if already connected
* @throws NullPointerException if key is null
* @see #getRequestProperty(java.lang.String)
*/
public void setRequestProperty(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.
*
* @param key the keyword by which the request is known
* (e.g., "accept").
* @param value the value associated with it.
* @throws IllegalStateException if already connected
* @throws NullPointerException if key is null
* @see #getRequestProperties(java.lang.String)
* @since 1.4
*/
public void addRequestProperty(String key, String value) { }
/**
* Returns the value of the named general request property for this
* connection.
*
* @param key the keyword by which the request is known (e.g., "accept").
* @return 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 #setRequestProperty(java.lang.String, java.lang.String)
*/
public String getRequestProperty(String key) {
return null;
}
/**
* 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.
*
* @return a Map of the general request properties for this connection.
* @throws IllegalStateException if already connected
* @since 1.4
*/
public Map getRequestProperties() {
return null;
}
/**
* 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.
*
* @param fac the desired factory.
* @exception Error if the factory has already been defined.
* @exception SecurityException if a security manager exists and its
* checkSetFactory method doesn't allow the operation.
* @see java.net.ContentHandlerFactory
* @see java.net.URLConnection#getContent()
* @see SecurityManager#checkSetFactory
*/
public static synchronized void
setContentHandlerFactory(ContentHandlerFactory fac)
{ }
/**
* 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.
*
* @param fname a filename.
* @return a guess as to what the content type of the object is,
* based upon its file name.
* @see java.net.URLConnection#getContentType()
*/
public static String guessContentTypeFromName(String fname) {
return null;
}
/**
* 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.
*
* @param is an input stream that supports marks.
* @return a guess at the content type, or null if none
* can be determined.
* @exception IOException if an I/O error occurs while reading the
* input stream.
* @see java.io.InputStream#mark(int)
* @see java.io.InputStream#markSupported()
* @see java.net.URLConnection#getContentType()
*/
public static String guessContentTypeFromStream(InputStream is)
throws IOException
{
return null;
}
}