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The Apache Commons JEXL library is an implementation of the JSTL Expression Language with extensions.
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.commons.jexl3.scripting;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.PrintWriter;
import java.io.Reader;
import java.io.Writer;
import javax.script.AbstractScriptEngine;
import javax.script.Bindings;
import javax.script.Compilable;
import javax.script.CompiledScript;
import javax.script.ScriptContext;
import javax.script.ScriptEngine;
import javax.script.ScriptEngineFactory;
import javax.script.ScriptException;
import javax.script.SimpleBindings;
import org.apache.commons.jexl3.JexlBuilder;
import org.apache.commons.jexl3.JexlContext;
import org.apache.commons.jexl3.JexlEngine;
import org.apache.commons.jexl3.JexlScript;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
/**
* Implements the JEXL ScriptEngine for JSF-223.
*
* This implementation gives access to both ENGINE_SCOPE and GLOBAL_SCOPE bindings.
* When a JEXL script accesses a variable for read or write,
* this implementation checks first ENGINE and then GLOBAL scope.
* The first one found is used.
* If no variable is found, and the JEXL script is writing to a variable,
* it will be stored in the ENGINE scope.
*
*
* The implementation also creates the "JEXL" script object as an instance of the
* class {@link JexlScriptObject} for access to utility methods and variables.
*
* See
* Java Scripting API
* Javadoc.
*
* @since 2.0
*/
public class JexlScriptEngine extends AbstractScriptEngine implements Compilable {
/** The logger. */
private static final Log LOG = LogFactory.getLog(JexlScriptEngine.class);
/** The shared expression cache size. */
private static final int CACHE_SIZE = 512;
/** Reserved key for context (mandated by JSR-223). */
public static final String CONTEXT_KEY = "context";
/** Reserved key for JexlScriptObject. */
public static final String JEXL_OBJECT_KEY = "JEXL";
/** The JexlScriptObject instance. */
private final JexlScriptObject jexlObject;
/** The factory which created this instance. */
private final ScriptEngineFactory parentFactory;
/** The JEXL EL engine. */
private final JexlEngine jexlEngine;
/**
* Default constructor.
*
* Only intended for use when not using a factory.
* Sets the factory to {@link JexlScriptEngineFactory}.
*/
public JexlScriptEngine() {
this(FactorySingletonHolder.DEFAULT_FACTORY);
}
/**
* Implements engine and engine context properties for use by JEXL scripts.
* Those properties are allways bound to the default engine scope context.
*
* The following properties are defined:
*
*
* - in - refers to the engine scope reader that defaults to reading System.err
* - out - refers the engine scope writer that defaults to writing in System.out
* - err - refers to the engine scope writer that defaults to writing in System.err
* - logger - the JexlScriptEngine logger
* - System - the System.class
*
*
* @since 2.0
*/
public class JexlScriptObject {
/**
* Gives access to the underlying JEXL engine shared between all ScriptEngine instances.
* Although this allows to manipulate various engine flags (lenient, debug, cache...)
* for all JexlScriptEngine instances, you probably should only do so
* if you are in strict control and sole user of the JEXL scripting feature.
*
* @return the shared underlying JEXL engine
*/
public JexlEngine getEngine() {
return jexlEngine;
}
/**
* Gives access to the engine scope output writer (defaults to System.out).
*
* @return the engine output writer
*/
public PrintWriter getOut() {
final Writer out = context.getWriter();
if (out instanceof PrintWriter) {
return (PrintWriter) out;
} else if (out != null) {
return new PrintWriter(out, true);
} else {
return null;
}
}
/**
* Gives access to the engine scope error writer (defaults to System.err).
*
* @return the engine error writer
*/
public PrintWriter getErr() {
final Writer error = context.getErrorWriter();
if (error instanceof PrintWriter) {
return (PrintWriter) error;
} else if (error != null) {
return new PrintWriter(error, true);
} else {
return null;
}
}
/**
* Gives access to the engine scope input reader (defaults to System.in).
*
* @return the engine input reader
*/
public Reader getIn() {
return context.getReader();
}
/**
* Gives access to System class.
*
* @return System.class
*/
public Class getSystem() {
return System.class;
}
/**
* Gives access to the engine logger.
*
* @return the JexlScriptEngine logger
*/
public Log getLogger() {
return LOG;
}
}
/**
* Create a scripting engine using the supplied factory.
*
* @param factory the factory which created this instance.
* @throws NullPointerException if factory is null
*/
public JexlScriptEngine(final ScriptEngineFactory factory) {
if (factory == null) {
throw new NullPointerException("ScriptEngineFactory must not be null");
}
parentFactory = factory;
jexlEngine = EngineSingletonHolder.DEFAULT_ENGINE;
jexlObject = new JexlScriptObject();
}
@Override
public Bindings createBindings() {
return new SimpleBindings();
}
@Override
public Object eval(final Reader reader, final ScriptContext context) throws ScriptException {
// This is mandated by JSR-223 (see SCR.5.5.2 Methods)
if (reader == null || context == null) {
throw new NullPointerException("script and context must be non-null");
}
return eval(readerToString(reader), context);
}
@Override
public Object eval(final String script, final ScriptContext context) throws ScriptException {
// This is mandated by JSR-223 (see SCR.5.5.2 Methods)
if (script == null || context == null) {
throw new NullPointerException("script and context must be non-null");
}
// This is mandated by JSR-223 (end of section SCR.4.3.4.1.2 - JexlScript Execution)
context.setAttribute(CONTEXT_KEY, context, ScriptContext.ENGINE_SCOPE);
try {
JexlScript jexlScript = jexlEngine.createScript(script);
JexlContext ctxt = new JexlContextWrapper(context);
return jexlScript.execute(ctxt);
} catch (Exception e) {
throw new ScriptException(e.toString());
}
}
@Override
public ScriptEngineFactory getFactory() {
return parentFactory;
}
@Override
public CompiledScript compile(final String script) throws ScriptException {
// This is mandated by JSR-223
if (script == null) {
throw new NullPointerException("script must be non-null");
}
try {
JexlScript jexlScript = jexlEngine.createScript(script);
return new JexlCompiledScript(jexlScript);
} catch (Exception e) {
throw new ScriptException(e.toString());
}
}
@Override
public CompiledScript compile(final Reader script) throws ScriptException {
// This is mandated by JSR-223
if (script == null) {
throw new NullPointerException("script must be non-null");
}
return compile(readerToString(script));
}
/**
* Read from a reader into a local buffer and return a String with
* the contents of the reader.
*
* @param scriptReader to be read.
* @return the contents of the reader as a String.
* @throws ScriptException on any error reading the reader.
*/
private static String readerToString(Reader scriptReader) throws ScriptException {
StringBuilder buffer = new StringBuilder();
BufferedReader reader;
if (scriptReader instanceof BufferedReader) {
reader = (BufferedReader) scriptReader;
} else {
reader = new BufferedReader(scriptReader);
}
try {
String line;
while ((line = reader.readLine()) != null) {
buffer.append(line).append('\n');
}
return buffer.toString();
} catch (IOException e) {
throw new ScriptException(e);
}
}
/**
* Holds singleton JexlScriptEngineFactory (IODH).
*/
private static class FactorySingletonHolder {
/** non instantiable. */
private FactorySingletonHolder() {}
/** The engine factory singleton instance. */
private static final JexlScriptEngineFactory DEFAULT_FACTORY = new JexlScriptEngineFactory();
}
/**
* Holds singleton JexlScriptEngine (IODH).
* A single JEXL engine and JexlUberspect is shared by all instances of JexlScriptEngine.
*/
private static class EngineSingletonHolder {
/** non instantiable. */
private EngineSingletonHolder() {}
/** The JEXL engine singleton instance. */
private static final JexlEngine DEFAULT_ENGINE = new JexlBuilder().logger(LOG).cache(CACHE_SIZE).create();
}
/**
* Wrapper to help convert a JSR-223 ScriptContext into a JexlContext.
*
* Current implementation only gives access to ENGINE_SCOPE binding.
*/
private final class JexlContextWrapper implements JexlContext {
/** The wrapped script context. */
private final ScriptContext scriptContext;
/**
* Creates a context wrapper.
*
* @param theContext the engine context.
*/
private JexlContextWrapper (final ScriptContext theContext){
scriptContext = theContext;
}
@Override
public Object get(final String name) {
final Object o = scriptContext.getAttribute(name);
if (JEXL_OBJECT_KEY.equals(name)) {
if (o != null) {
LOG.warn("JEXL is a reserved variable name, user defined value is ignored");
}
return jexlObject;
}
return o;
}
@Override
public void set(final String name, final Object value) {
int scope = scriptContext.getAttributesScope(name);
if (scope == -1) { // not found, default to engine
scope = ScriptContext.ENGINE_SCOPE;
}
scriptContext.getBindings(scope).put(name , value);
}
@Override
public boolean has(final String name) {
Bindings bnd = scriptContext.getBindings(ScriptContext.ENGINE_SCOPE);
return bnd.containsKey(name);
}
}
/**
* Wrapper to help convert a JEXL JexlScript into a JSR-223 CompiledScript.
*/
private final class JexlCompiledScript extends CompiledScript {
/** The underlying JEXL expression instance. */
private final JexlScript script;
/**
* Creates an instance.
*
* @param theScript to wrap
*/
private JexlCompiledScript(final JexlScript theScript) {
script = theScript;
}
@Override
public String toString() {
return script.getSourceText();
}
@Override
public Object eval(final ScriptContext context) throws ScriptException {
// This is mandated by JSR-223 (end of section SCR.4.3.4.1.2 - JexlScript Execution)
context.setAttribute(CONTEXT_KEY, context, ScriptContext.ENGINE_SCOPE);
try {
JexlContext ctxt = new JexlContextWrapper(context);
return script.execute(ctxt);
} catch (Exception e) {
throw new ScriptException(e.toString());
}
}
@Override
public ScriptEngine getEngine() {
return JexlScriptEngine.this;
}
}
}
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