Java Doc for JavaEngine.java in  » Scripting » bsf-2.4.0 » org » apache » bsf » engines » java » Java Source Code / Java DocumentationJava Source Code and Java Documentation

The Java code must be written script-style -- that is, just the body of the function, without class or method headers or footers. The JavaEngine will generate those via a "boilerplate" wrapper:

 
 import java.lang.*;
 import java.util.*;
 public class $$CLASSNAME$$ {
 static public Object BSFJavaEngineEntry(org.apache.bsf.BSFManager bsf) {
 // Your code will be placed here
 }
 }
 
 

If you use the placeholder string $$CLASSNAME$$ elsewhere in your script -- including within text strings -- BSFJavaEngine will replace it with the generated name of the class before the Java code is compiled.

Hazards:

NOTE that it is your responsibility to convert the code into an acceptable Java string. If you're invoking the JavaEngine directly (as in the JSPLikeInJava example) that means \"quoting\" characters that would otherwise cause trouble.

ALSO NOTE that it is your responsibility to return an object, or null in lieu thereof!

Since the code has to be compiled to a Java classfile, invoking it involves a fair amount of computation to load and execute the compiler. We are currently making an attempt to manage that by caching the class after it has been loaded, but the indexing is fairly primitive. It has been suggested that the Bean Scripting Framework may want to support preload-and-name-script and execute-preloaded-script-by-name options to provide better control over when and how much overhead occurs.

author:
   Joe Kesselman

Note that Java compilation imposes serious overhead, but in exchange you get full Java performance once the classes have been created (minus the cache lookup cost).

Nobody knows whether javac is threadsafe. I'm going to serialize access to protect it.

There is no published API for invoking javac as a class. There's a trick that seems to work for Java 1.1.x, but it stopped working in Java 1.2. We will attempt to use it, then if necessary fall back on invoking javac via the command line.