When the JVM begins to process an application, it can optionally load an instance of the SecurityManager class. Every attempt to access external resources, such as executing a read or write to a file, will need to obtain permission from the security manager.

Prior to version 1.2, a SecurityManager subclass would override methods such as checkRead() and checkWrite() with code that examined the request and threw an exception if it was judged invalid. With version 1.2 a more elaborate and flexible Permissions and Security Policy file scheme was put into effect.

In Chapter 14 : HTTP Server - SecurityManager we look further at how to set up a security manager.

Note that the application in a browser that runs applets has by default an extremely restrictive security manager that blocks virtually all accesses other than reading files from the applets site and opening web pages to other sites.

References & Web Resources

	Part I	Part II	Part III
Java Core	1  2  3  4  5  6  7  8  9  10  11  12	13 14 15 16 17 18 19 20 21	22 23 24
Supplements	1  2  3  4  5  6  7  8  9  10  11  12
Tech	1  2  3  4  5  6  7  8  9  10  11  12
Physics	1  2  3  4  5  6  7  8  9  10  11  12

Java is a trademark of Sun Microsystems, Inc.