Accessing Native methods from a Java Applet
by Sanket Bakshi, s.bakshi@ebsolutech.com |
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Previous
section: Overview
The
applet is a Java code that has a capability to embed itself into a HTML page.
The applet life cycle starts when the page in which it is embedded is loaded.
An applet is created by extending the Applet class in the java. Applet package.
The java.applet package provides
an API that gives applets some capabilities that applications don't have.
Here are
some other things that current browsers and other applet viewers let applets
do:
o Applets can
usually make network connections to the host they came from.
o Applets running
within a Web browser can easily cause HTML documents to be displayed.
o Applets can
invoke public methods of other applets on the same page.
o Applets that are
loaded from the local file system (from a directory in the user's CLASSPATH) have none of the restrictions that applets
loaded over the network do.
o Although most
applets stop running once you leave their page, they don't have to.
o The applets can
also incorporate into themselves a dynamic GUI.
Every
browser implements security policies to keep applets from compromising system
security. However, the implementation of the security policies differs from
browser to browser. Also, security policies are subject to change. For example,
if a browser is developed for use only in trusted environments, then its
security policies will likely be much more lax than those described here.
Current
browsers impose the following restrictions on any applet that is loaded over
the network:
o An applet cannot
load libraries or define native methods.
o It cannot
ordinarily read or write files on the host that's executing it.
o It cannot make
network connections except to the host that it came from.
o It cannot start
any program on the host that's executing it.
o It cannot read
certain system properties.
o Windows that an
applet brings up look different than windows that an application brings up.
Each
browser has a SecurityManager object that
implements its security policies. When a SecurityManager detects a violation, it throws a SecurityException. Your applet can
catch this SecurityException and react appropriately.
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