URLConnections - Java Network Programming - page 223

Pass each name and value in the query string to URLEncoder.encode() before
adding it to the query string.
4. Open a URLConnection to the URL of the program that will accept the data.
5. Set doOutput to true by invoking setDoOutput(true) .
6. Write the query string onto the URLConnection 's OutputStream .
7. Close the URLConnection 's OutputStream .
8. Read the server response from the URLConnection 's InputStream .
GET should only be used for safe operations that can be bookmarked and linked to. POST
should be used for unsafe operations that should not be bookmarked or linked to.
The getOutputStream() method is also used for the PUT request method, a means of
storing files on a web server. The data to be stored is written onto the OutputStream
that getOutputStream() returns. However, this can be done only from within the
HttpURLConnection subclass of URLConnection , so discussion of PUT will have to wait
a little while.
Security Considerations for URLConnections
URLConnection objects are subject to all the usual security restrictions about making
network connections, reading or writing files, and so forth. For instance, a URLConnec
tion can be created by an untrusted applet only if the URLConnection is pointing to the
host that the applet came from. However, the details can be a little tricky because dif‐
ferent URL schemes and their corresponding connections can have different security
implications. For example, a jar URL that points into the applet's own jar file should be
fine. However, a file URL that points to a local hard drive should not be.
Before attempting to connect a URL, you may want to know whether the connection
will be allowed. For this purpose, the URLConnection class has a getPermission()
method:
public Permission getPermission () throws IOException
This returns a java.security.Permission object that specifies what permission is
needed to connect to the URL. It returns null if no permission is needed (e.g., there's
no security manager in place). Subclasses of URLConnection return different subclasses
of java.security.Permission . For instance, if the underlying URL points to
www.gwbush.com , getPermission() returns a java.net.SocketPermission for the
host www.gwbush.com with the connect and resolve actions.