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Java in a Nutshell

Previous Chapter 28
The java.net Package

28.23 java.net.URLConnection (JDK 1.0)

This abstract class defines a network connection to an object specified by a URL. URL.openConnection() returns a URLConnection instance. You would use a URLConnection object when you want more control over the downloading of data than is available through the simpler URL methods.

connect() actually performs the network connection. Other methods that depend on being connected will call this method. getContent() returns the data referred to by the URL, parsed into an appropriate type of Object. If the URL protocol supports read and write operations, then getInputStream() and getOutputStream() respectively return input and output streams to the object referred to by the URL.

getContentLength(), getContentType(), getContentEncoding(), getExpiration(), getDate(), and getLastModified() return the appropriate information about the object referred to by the URL, if that information can be determined (e.g., from HTTP header fields). getHeaderField() returns an HTTP header field specified by name or by number. getHeaderFieldInt() and getHeaderFieldDate() return the value of a named header field parsed as an integer or a date.

There are a number of options that you may specify to control how the URLConnection behaves. These options are set with the various set() methods, and may be queried with corresponding get() methods. The options must be set before the connect() method is called. setDoInput() and setDoOutput() allow you to specify whether you use the URLConnection for input and/or output. The default is input-only. setAllowUserInteraction() specifies whether user interaction (such as typing a password) is allowed during the data transfer. The initial default is false. setDefaultAllowUserInteraction() is a class method that allows you to change the default value for user interaction. setUseCaches() allows you to specify whether a cached version of the URL may be used. You can set this to false to force a URL to be reloaded. setDefaultUseCaches() sets the default value for setUseCaches(). setIfModifiedSince() allows you to specify that a URL should not be fetched (if it is possible to determine its modification date) unless it has been modified since a specified time.

public abstract class URLConnection extends Object {
    // Protected Constructor
            protected URLConnection(URL url);
    // Class Variables
        1.1public static FileNameMap fileNameMap;
    // Protected Instance Variables
            protected boolean allowUserInteraction;
            protected boolean connected;
            protected boolean doInput;
            protected boolean doOutput;
            protected long ifModifiedSince;
            protected URL url;
            protected boolean useCaches;
    // Class Methods
            public static boolean getDefaultAllowUserInteraction();
            public static String getDefaultRequestProperty(String key);
            protected static String guessContentTypeFromName(String fname);
            public static String guessContentTypeFromStream(InputStream is) throws IOException;
            public static synchronized void setContentHandlerFactory(ContentHandlerFactory fac);
            public static void setDefaultAllowUserInteraction(boolean defaultallowuserinteraction);
            public static void setDefaultRequestProperty(String key, String value);
    // Public Instance Methods
            public abstract void connect() throws IOException;
            public boolean getAllowUserInteraction();
            public Object getContent() throws IOException;
            public String getContentEncoding();
            public int getContentLength();
            public String getContentType();
            public long getDate();
            public boolean getDefaultUseCaches();
            public boolean getDoInput();
            public boolean getDoOutput();
            public long getExpiration();
            public String getHeaderField(String name);
            public String getHeaderField(int n);
            public long getHeaderFieldDate(String name, long Default);
            public int getHeaderFieldInt(String name, int Default);
            public String getHeaderFieldKey(int n);
            public long getIfModifiedSince();
            public InputStream getInputStream() throws IOException;
            public long getLastModified();
            public OutputStream getOutputStream() throws IOException;
            public String getRequestProperty(String key);
            public URL getURL();
            public boolean getUseCaches();
            public void setAllowUserInteraction(boolean allowuserinteraction);
            public void setDefaultUseCaches(boolean defaultusecaches);
            public void setDoInput(boolean doinput);
            public void setDoOutput(boolean dooutput);
            public void setIfModifiedSince(long ifmodifiedsince);
            public void setRequestProperty(String key, String value);
            public void setUseCaches(boolean usecaches);
            public String toString();  // Overrides Object

Extended By:


Passed To:


Returned By:

URL.openConnection(), URLStreamHandler.openConnection()

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