Accessing Native methods from a Java Applet

www.ebsolutech.com

by Sanket Bakshi, s.bakshi@ebsolutech.com

Overview

The Java Sandbox

The Java security model is one of the key architectural features that make Java a technology for networked environments. This is necessary as the security is the major concern when the computer is hooked to a network. Also, the Java code, many a times, has to be downloaded onto the client machine before executing it, like in case of an applet or a Jini service object. This makes the computer more vulnerable to network attacks. The Java security model, better known as the Sandbox addresses this security concern. In a Sandbox, all the code that comes from a source that is not trusted is allowed to run in a restricted environment of the ‘Sandbox’. This gives the code very few privileges and does not allow it to tamper with the system. Operations like reading or writing a file or loading a native library etc. performed by such code are strongly opposed by the Sandbox architecture.

Digital Certificates

Digital certificates are online documents that authenticate user identities, provide the codes that encrypt and decrypt messages over the Web, and ensure that transmitted data has not been altered.

A Certificate Authority (CA) is the Web-based mechanism that distributes and revokes certificates and guarantees data integrity by digitally "signing" a user's certificate.

JNI

The JNI (Java Native Interface) technology is a practical extension of the NMI (Native Method Interface) model provided in the JDK 1.0. The JNI allows a Java programmer, access to any native resources. The JNI can be used to access already written native code or in cases where platform dependant functionalities not provided by Java are required or it can be even used when a low level language – e.g. Assembly language, performs a critical task beyond the scope of Java.

Java Plug-ins

The Java Plug-in software allows Java applets and Java Beans components to run in a browser using Sun's Java Runtime Environment, instead of the browser's default Java runtime. The Java Plug-in works with Netscape Navigator and Microsoft Internet Explorer. The plug-in requires the <OBJECT> and <EMBED> tags be embedded in the HTML page instead of the applet tag. This allows code compatibility between the browsers as a common Runtime environment is created which works independent of the browser.

Browser Versions

Not all versions of Navigator and Explorer understand signed applets. In fact, only the following do:

Many of the Java functions and facilities are also not supported by all the browsers available. Like for instance, Internet Explorer 4.0 does not support the use of JFC (Java Foundation Classes).

Nevertheless, the use of a Java Plug-in reduces these compatibility problems to a great extent. The use of a plug-in as mentioned earlier, runs the Java code in a Runtime Environment, which is common for all the browsers. The Plug-in overrides the default JRE provided by the browser.