標籤彙整: java 教學 書

XML is a popular data format for several reasons: it is human readable, self-describing, and portable. Unfortunately, many Java-based XML parsers are very large; for example, Sun Microsystems’ jaxp.jar and parser.jar libraries are 1.4 MB each. If you are running with limited memory (for example, in a J2ME (Java 2 Platform, Micro Edition) environment), or bandwidth is at a premium (for example, in an applet), using those large parsers might not be a viable solution.

Those libraries’ large size is partly due to having a lot of functionality—perhaps more than you require. They validate XML DTDs (document type definitions), possibly schemas, and more. However, you might already know that your application will receive valid XML. Also, you might already decide that you want just the UTF-8 character set. Therefore, you really want event-based processing of XML elements and translation of standard XML entities—you want a nonvalidating parser.

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You can easily package an application’s entire set of classes and resources into a Java Archive (JAR). In fact, that is one goal of having jar files. Another is to let users easily execute the application stored in the archive. Why then are jar files second-class citizens in the Java universe—functioning only as archives—when they can be first class, right alongside native executables?

To execute a jar file, you can use the

java

command’s

-jar

option. For example, say you have a runnable jar file called

myjar.jar

. Because the file is runnable, you can execute it like this:

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