org.apache.bsf.engines.java

Class JavaEngine

java.lang.Object

org.apache.bsf.util.BSFEngineImpl

org.apache.bsf.engines.java.JavaEngine

All Implemented Interfaces:

java.beans.PropertyChangeListener, java.util.EventListener, BSFEngine

public class JavaEngine
extends BSFEngineImpl

This is the interface to Java from the Bean Scripting Framework.

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
   }
 }
 
 

$$CLASSNAME$$ will be replaced by a generated classname of the form BSFJava*, and the bsf parameter can be used to retrieve application objects registered with the Bean Scripting Framework.

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.

Field Summary

Fields inherited from class org.apache.bsf.util.BSFEngineImpl

classLoader, classPath, declaredBeans, lang, mgr, tempDir

Constructor Summary

Constructors

Constructor and Description
JavaEngine() Constructor.

Method Summary

Modifier and Type	Method and Description
java.lang.Object	call(java.lang.Object object, java.lang.String method, java.lang.Object[] args) This is used by an application to call into the scripting engine to make a function/method call.
void	compileScript(java.lang.String source, int lineNo, int columnNo, java.lang.Object script, CodeBuffer cb) Default impl of compileScript - generates code that'll create a new manager, and execute the script.
java.lang.Object	eval(java.lang.String source, int lineNo, int columnNo, java.lang.Object oscript) This is used by an application to evaluate a string containing some expression.
void	initialize(BSFManager mgr, java.lang.String lang, java.util.Vector declaredBeans) initialize the engine; called right after construction by the manager.

Methods inherited from class org.apache.bsf.util.BSFEngineImpl

apply, compileApply, compileExpr, declareBean, exec, iexec, propertyChange, terminate, undeclareBean

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

JavaEngine

public JavaEngine()

Constructor.

Method Detail

call

public java.lang.Object call(java.lang.Object object,
                             java.lang.String method,
                             java.lang.Object[] args)
                      throws BSFException

Description copied from interface: BSFEngine

This is used by an application to call into the scripting engine to make a function/method call. The "object" argument is the object whose method is to be called, if that applies. For non-OO languages, this is typically ignored and should be given as null. For pretend-OO languages such as VB, this would be the (String) name of the object. The arguments are given in the args array.

Parameters:

object - object on which to make the call

method - name of the method / procedure to call

args - the arguments to be given to the procedure

Throws:

BSFException - if anything goes wrong while eval'ing a BSFException is thrown. The reason indicates the problem.

compileScript

public void compileScript(java.lang.String source,
                          int lineNo,
                          int columnNo,
                          java.lang.Object script,
                          CodeBuffer cb)
                   throws BSFException

Description copied from class: BSFEngineImpl

Default impl of compileScript - generates code that'll create a new manager, and execute the script.

Specified by:

compileScript in interface BSFEngine

Overrides:

compileScript in class BSFEngineImpl

Parameters:

source - (context info) the source of this script (e.g., filename)

lineNo - (context info) the line number in source for script

columnNo - (context info) the column number in source for script

script - the script to compile

cb - the CodeBuffer to compile into

Throws:

BSFException - if anything goes wrong while compiling a BSFException is thrown. The reason indicates the problem.

eval

public java.lang.Object eval(java.lang.String source,
                             int lineNo,
                             int columnNo,
                             java.lang.Object oscript)
                      throws BSFException

This is used by an application to evaluate a string containing some expression. It should store the "bsf" handle where the script can get to it, for callback purposes.

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.

Parameters:

source - (context info) the source of this expression (e.g., filename)

lineNo - (context info) the line number in source for expr

columnNo - (context info) the column number in source for expr

oscript - the expression to evaluate

Throws:

BSFException - if anything goes wrong while eval'ing a BSFException is thrown. The reason indicates the problem.

initialize

public void initialize(BSFManager mgr,
                       java.lang.String lang,
                       java.util.Vector declaredBeans)
                throws BSFException

Description copied from class: BSFEngineImpl

initialize the engine; called right after construction by the manager. Declared beans are simply kept in a vector and that's it. Subclasses must do whatever they want with it.

Specified by:

initialize in interface BSFEngine

Overrides:

initialize in class BSFEngineImpl

Parameters:

mgr - The BSFManager that's hosting this engine.

lang - Language string which this engine is handling.

declaredBeans - Vector of BSFDeclaredObject containing beans that should be declared into the language runtime at init time as best as possible.

Throws:

BSFException - if anything goes wrong while init'ing a BSFException is thrown. The reason indicates the problem.