Security and the Network

As much as we look forward to writing a great variety of powerful network-based applications, our efforts may be limited because of security concerns. Many Web browsers, such as Mozilla and Microsoft Internet Explorer, by default prohibit Java applets from doing file processing on the machines on which they execute. Think about it. A Java applet is designed to be sent to your browser via an HTML document that could be downloaded from any Web server in the world. Often you will know very little about the sources of Java applets that will execute on your system. To allow these applets free rein with your files could be disastrous.

A more subtle situation occurs with limiting the machines to which executing applets can make network connections. To build truly collaborative applications, we would ideally like to have our applets communicate with machines almost anywhere. The Java security manager in a Web browser often restricts an applet so that it can communicate only with the machine from which it was originally downloaded.

These restrictions may seem too strict. However, the Java Security API now provides capabilities for digitally signed applets that will enable browsers to determine whether an applet is downloaded from a trusted source. A trusted applet can be given additional access to the computer on which it is executing. The features of the Java Security API and additional networking capabilities are discussed in our text Advanced Java 2 Platform How to Program.