/src/bsh/BshScriptEngine.java

package bsh;



import javax.script.AbstractScriptEngine;

import javax.script.Bindings;

import javax.script.Compilable;

import javax.script.CompiledScript;

import javax.script.Invocable;

import javax.script.ScriptContext;

import javax.script.ScriptEngine;

import javax.script.ScriptEngineFactory;

import javax.script.ScriptException;

import javax.script.SimpleBindings;

import java.io.IOException;

import java.io.OutputStream;

import java.io.PrintStream;

import java.io.Reader;

import java.io.Writer;

import java.util.ArrayList;

import java.util.Collections;

import java.util.HashMap;

import java.util.List;

import java.util.Map;



/*

	Adopted from http://ikayzo.org/svn/beanshell/BeanShell/engine/src/bsh/engine/BshScriptEngine.java

	Notes

	This engine supports open-ended pluggable scriptcontexts

*/



public class BshScriptEngine extends AbstractScriptEngine implements Compilable, Invocable {

	// The BeanShell global namespace for the interpreter is stored in the

	// engine scope map under this key.

	static final String engineNameSpaceKey = "org_beanshell_engine_namespace";



	private BshScriptEngineFactory factory;

	private bsh.Interpreter interpreter;





	public BshScriptEngine() {

		this(null);

	}





	public BshScriptEngine(BshScriptEngineFactory factory) {

		this.factory = factory;

		getInterpreter(); // go ahead and prime the interpreter now

	}





	protected Interpreter getInterpreter() {

		if (interpreter == null) {

			this.interpreter = new bsh.Interpreter();

			interpreter.setNameSpace(null); // should always be set by context

		}



		return interpreter;

	}





	public Object eval(String script, ScriptContext scriptContext) throws ScriptException {

		return evalSource(script, scriptContext);

	}





	public Object eval(Reader reader, ScriptContext scriptContext) throws ScriptException {

		return evalSource(reader, scriptContext);

	}



	/*

		This is the primary implementation method.

		We respect the String/Reader difference here in BeanShell because

		BeanShell will do a few extra things in the string case... e.g.

		tack on a trailing ";" semicolon if necessary.

	*/





	private Object evalSource(Object source, ScriptContext scriptContext) throws ScriptException {

		bsh.NameSpace contextNameSpace = getEngineNameSpace(scriptContext);

		Interpreter bsh = getInterpreter();

		bsh.setNameSpace(contextNameSpace);



		bsh.setOut(toPrintStream(scriptContext.getWriter()));

		bsh.setErr(toPrintStream(scriptContext.getErrorWriter()));



		try {

			if (source instanceof Reader) {

				return bsh.eval((Reader) source);

			} else {

				return bsh.eval((String) source);

			}

		} catch (ParseException e) {

			// explicit parsing error

			throw new ScriptException(e.toString(), e.getErrorSourceFile(), e.getErrorLineNumber());

		} catch (TargetError e) {

			// The script threw an application level exception

			// set it as the cause ?

			ScriptException se = new ScriptException(e.toString(), e.getErrorSourceFile(), e.getErrorLineNumber());

			se.initCause(e.getTarget());

			throw se;

		} catch (EvalError e) {

			// The script couldn't be evaluated properly

			throw new ScriptException(e.toString(), e.getErrorSourceFile(), e.getErrorLineNumber());

		} catch (InterpreterError e) {

			// The interpreter had a fatal problem

			throw new ScriptException(e.toString());

		}

	}





	private PrintStream toPrintStream(final Writer writer) {

		// This is a big hack, convert writer to PrintStream

		return new PrintStream(new WriterOutputStream(writer));

	}





	/*

		Check the context for an existing global namespace embedded

		in the script context engine scope.  If none exists, ininitialize the

		context with one.

	*/





	private static NameSpace getEngineNameSpace(ScriptContext scriptContext) {

		NameSpace ns = (NameSpace) scriptContext.getAttribute(engineNameSpaceKey, ScriptContext.ENGINE_SCOPE);



		if (ns == null) {

			// Create a global namespace for the interpreter

			Map<String, Object> engineView = new ScriptContextEngineView(scriptContext);

			ns = new ExternalNameSpace(null/*parent*/, "javax_script_context", engineView);



			scriptContext.setAttribute(engineNameSpaceKey, ns, ScriptContext.ENGINE_SCOPE);

		}



		return ns;

	}





	public Bindings createBindings() {

		return new SimpleBindings();

	}





	public ScriptEngineFactory getFactory() {

		if (factory == null) {

			factory = new BshScriptEngineFactory();

		}

		return factory;

	}





	/**

	 * Compiles the script (source represented as a {@code String}) for later

	 * execution.

	 *

	 * @param script The source of the script, represented as a {@code String}.

	 * @return An subclass of {@code CompiledScript} to be executed later

	 *         using one of the {@code eval} methods of {@code CompiledScript}.

	 * @throws ScriptException	  if compilation fails.

	 * @throws NullPointerException if the argument is null.

	 */



	public CompiledScript compile(String script) throws ScriptException {

		try {

			final PreparsedScript preparsed = new PreparsedScript(script);

			return new CompiledScript() {



				@Override

				public Object eval(ScriptContext context) throws ScriptException {

					final HashMap<String, Object> map = new HashMap<String, Object>();

					final List<Integer> scopes = new ArrayList<Integer>(context.getScopes());

					Collections.sort(scopes); // lowest scope at first pos

					Collections.reverse(scopes); // highest scope at first pos

					for (final Integer scope : scopes) {

						map.putAll(context.getBindings(scope));

					}

					preparsed.setOut(toPrintStream(context.getWriter()));

					preparsed.setErr(toPrintStream(context.getErrorWriter()));

					try {

						return preparsed.invoke(map);

					} catch (final EvalError e) {

						throw constructScriptException(e);

					}

				}





				@Override

				public ScriptEngine getEngine() {

					return BshScriptEngine.this;

				}



			};

		} catch (final EvalError e) {

			throw constructScriptException(e);

		}

	}





	private ScriptException constructScriptException(final EvalError e) {

		return new ScriptException(e.getMessage(), e.getErrorSourceFile(), e.getErrorLineNumber());

	}





	private static String convertToString(Reader reader) throws IOException {

		final StringBuffer buffer = new StringBuffer(64);

		char[] cb = new char[64];

		int len;

		while ((len = reader.read(cb)) != -1) {

			buffer.append(cb, 0, len);

		}

		return buffer.toString();

	}



	

	/**

	 * Compiles the script (source read from {@code Reader}) for later

	 * execution.  Functionality is identical to {@code compile(String)} other

	 * than the way in which the source is passed.

	 *

	 * @param script The reader from which the script source is obtained.

	 * @return An implementation of {@code CompiledScript} to be executed

	 *         later using one of its {@code eval} methods of

	 *         {@code CompiledScript}.

	 * @throws ScriptException	  if compilation fails.

	 * @throws NullPointerException if argument is null.

	 */

	public CompiledScript compile(Reader script) throws ScriptException {

		try {

			return compile(convertToString(script));

		} catch (IOException e) {

			throw new ScriptException(e);

		}

	}





	/**

	 * Calls a procedure compiled during a previous script execution, which is

	 * retained in the state of the {@code ScriptEngine{@code .

	 *

	 * @param name The name of the procedure to be called.

	 * @param thiz If the procedure is a member  of a class defined in the script

	 *             and thiz is an instance of that class returned by a previous execution or

	 *             invocation, the named method is called through that instance. If classes are

	 *             not supported in the scripting language or if the procedure is not a member

	 *             function of any class, the argument must be {@code null}.

	 * @param args Arguments to pass to the procedure.  The rules for converting

	 *             the arguments to scripting variables are implementation-specific.

	 * @return The value returned by the procedure.  The rules for converting the

	 *         scripting variable returned by the procedure to a Java Object are

	 *         implementation-specific.

	 * @throws javax.script.ScriptException if an error occurrs during invocation

	 *                                      of the method.

	 * @throws NoSuchMethodException		if method with given name or matching argument

	 *                                      types cannot be found.

	 * @throws NullPointerException		 if method name is null.

	 */

	public Object invokeMethod(Object thiz, String name, Object... args) throws ScriptException, NoSuchMethodException {

		if (!(thiz instanceof bsh.This)) {

			throw new ScriptException("Illegal objec type: " + thiz.getClass());

		}



		bsh.This bshObject = (bsh.This) thiz;



		try {

			return bshObject.invokeMethod(name, args);

		} catch (ParseException e) {

			// explicit parsing error

			throw new ScriptException(e.toString(), e.getErrorSourceFile(), e.getErrorLineNumber());

		} catch (TargetError e) {

			// The script threw an application level exception

			// set it as the cause ?

			ScriptException se = new ScriptException(e.toString(), e.getErrorSourceFile(), e.getErrorLineNumber());

			se.initCause(e.getTarget());

			throw se;

		} catch (EvalError e) {

			// The script couldn't be evaluated properly

			throw new ScriptException(e.toString(), e.getErrorSourceFile(), e.getErrorLineNumber());

		} catch (InterpreterError e) {

			// The interpreter had a fatal problem

			throw new ScriptException(e.toString());

		}

	}





	/**

	 * Same as invoke(Object, String, Object...) with {@code null} as the

	 * first argument.  Used to call top-level procedures defined in scripts.

	 *

	 * @param args Arguments to pass to the procedure

	 * @return The value returned by the procedure

	 * @throws javax.script.ScriptException if an error occurrs during invocation

	 *                                      of the method.

	 * @throws NoSuchMethodException		if method with given name or matching

	 *                                      argument types cannot be found.

	 * @throws NullPointerException		 if method name is null.

	 */

	public Object invokeFunction(String name, Object... args) throws ScriptException, NoSuchMethodException {

		return invokeMethod(getGlobal(), name, args);

	}





	/**

	 * Returns an implementation of an interface using procedures compiled in the

	 * interpreter. The methods of the interface may be implemented using the

	 * {@code invoke} method.

	 *

	 * @param clasz The {@code Class} object of the interface to return.

	 * @return An instance of requested interface - null if the requested interface

	 *         is unavailable, i. e. if compiled methods in the

	 *         {@code ScriptEngine} cannot be found matching the ones in the

	 *         requested interface.

	 * @throws IllegalArgumentException if the specified {@code Class} object

	 *                                  does not exist or is not an interface.

	 */

	public <T> T getInterface(Class<T> clasz) {

		return clasz.cast(getGlobal().getInterface(clasz));

	}





	/**

	 * Returns an implementation of an interface using member functions of a

	 * scripting object compiled in the interpreter. The methods of the interface

	 * may be implemented using invoke(Object, String, Object...) method.

	 *

	 * @param thiz  The scripting object whose member functions are used to

	 *              implement the methods of the interface.

	 * @param clasz The {@code Class} object of the interface to return.

	 * @return An instance of requested interface - null if the requested

	 *         interface is unavailable, i. e. if compiled methods in the

	 *         {@code ScriptEngine} cannot be found matching the ones in the

	 *         requested interface.

	 * @throws IllegalArgumentException if the specified {@code Class} object

	 *                                  does not exist or is not an interface, or if the specified Object is null

	 *                                  or does not represent a scripting object.

	 */

	public <T> T getInterface(Object thiz, Class<T> clasz) {

		if (!(thiz instanceof bsh.This)) {

			throw new IllegalArgumentException("invalid object type: " + thiz.getClass());

		}



		bsh.This bshThis = (bsh.This) thiz;

		return clasz.cast(bshThis.getInterface(clasz));

	}





	private bsh.This getGlobal() {

		// requires 2.0b5 to make getThis() public

		return getEngineNameSpace(getContext()).getThis(getInterpreter());

	}



	/*

		This is a total hack.  We need to introduce a writer to the

		Interpreter.

	*/



	class WriterOutputStream extends OutputStream {



		Writer writer;





		WriterOutputStream(Writer writer) {

			this.writer = writer;

		}





		public void write(int b) throws IOException {

			writer.write(b);

		}





		public void flush() throws IOException {

			writer.flush();

		}





		public void close() throws IOException {

			writer.close();

		}

	}



}