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Groovy: A powerful, dynamic language for the JVM
/*
* 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 groovy.text;
import groovy.lang.*;
import java.io.IOException;
import java.io.Reader;
import java.security.AccessController;
import java.security.PrivilegedAction;
import java.util.Map;
import java.util.concurrent.atomic.AtomicInteger;
import org.codehaus.groovy.control.CompilationFailedException;
/**
* Processes template source files substituting variables and expressions into
* placeholders in a template source text to produce the desired output using
* a streaming approach. This engine has equivalent functionality to the
* {@link SimpleTemplateEngine} but creates the template using writable
* closures making it potentially more scalable for large templates or in streaming scenarios.
*
* The template engine uses JSP style <% %> script and <%= %> expression syntax
* or GString style expressions. The variable 'out' is bound to the writer that the template
* is being written to.
*
* Frequently, the template source will be in a file but here is a simple
* example providing the template as a string:
*
* def binding = [
* firstname : "Grace",
* lastname : "Hopper",
* accepted : true,
* title : 'Groovy for COBOL programmers'
* ]
* def engine = new groovy.text.GStringTemplateEngine()
* def text = '''\
* Dear <%= firstname %> $lastname,
*
* We <% if (accepted) print 'are pleased' else print 'regret' %> \
* to inform you that your paper entitled
* '$title' was ${ accepted ? 'accepted' : 'rejected' }.
*
* The conference committee.
* '''
* def template = engine.createTemplate(text).make(binding)
* println template.toString()
*
* This example uses a mix of the JSP style and GString style placeholders
* but you can typically use just one style if you wish. Running this
* example will produce this output:
*
* Dear Grace Hopper,
*
* We are pleased to inform you that your paper entitled
* 'Groovy for COBOL programmers' was accepted.
*
* The conference committee.
*
* The template engine can also be used as the engine for {@link groovy.servlet.TemplateServlet} by placing the
* following in your web.xml file (plus a corresponding servlet-mapping element):
*
* <servlet>
* <servlet-name>GStringTemplate</servlet-name>
* <servlet-class>groovy.servlet.TemplateServlet</servlet-class>
* <init-param>
* <param-name>template.engine</param-name>
* <param-value>groovy.text.GStringTemplateEngine</param-value>
* </init-param>
* </servlet>
*
* In this case, your template source file should be HTML with the appropriate embedded placeholders.
*
* @author [email protected]
* @author Paul King
*/
public class GStringTemplateEngine extends TemplateEngine {
private final ClassLoader parentLoader;
private static AtomicInteger counter = new AtomicInteger();
private static final boolean reuseClassLoader = Boolean.getBoolean("groovy.GStringTemplateEngine.reuseClassLoader");
public GStringTemplateEngine() {
this(GStringTemplate.class.getClassLoader());
}
public GStringTemplateEngine(ClassLoader parentLoader) {
this.parentLoader = parentLoader;
}
/* (non-Javadoc)
* @see groovy.text.TemplateEngine#createTemplate(java.io.Reader)
*/
public Template createTemplate(final Reader reader) throws CompilationFailedException, ClassNotFoundException, IOException {
return new GStringTemplate(reader, parentLoader);
}
private static class GStringTemplate implements Template {
final Closure template;
/**
* Turn the template into a writable Closure
* When executed the closure evaluates all the code embedded in the
* template and then writes a GString containing the fixed and variable items
* to the writer passed as a parameter
*
* For example:
*
* '<%= "test" %> of expr and <% test = 1 %>${test} script.'
*
*
* would compile into:
*
* { out -> out << "${"test"} of expr and "; test = 1 ; out << "${test} script."}.asWritable()
*
*
* @param reader
* @param parentLoader
* @throws CompilationFailedException
* @throws ClassNotFoundException
* @throws IOException
*/
GStringTemplate(final Reader reader, final ClassLoader parentLoader) throws CompilationFailedException, ClassNotFoundException, IOException {
final StringBuilder templateExpressions = new StringBuilder("package groovy.tmp.templates\n def getTemplate() { return { out -> out << \"\"\"");
boolean writingString = true;
while (true) {
int c = reader.read();
if (c == -1) break;
if (c == '<') {
c = reader.read();
if (c == '%') {
c = reader.read();
if (c == '=') {
parseExpression(reader, writingString, templateExpressions);
writingString = true;
continue;
} else {
parseSection(c, reader, writingString, templateExpressions);
writingString = false;
continue;
}
} else {
appendCharacter('<', templateExpressions, writingString);
writingString = true;
}
} else if (c == '"') {
appendCharacter('\\', templateExpressions, writingString);
writingString = true;
} else if (c == '$') {
appendCharacter('$', templateExpressions, writingString);
writingString = true;
c = reader.read();
if (c == '{') {
appendCharacter('{', templateExpressions, writingString);
writingString = true;
parseGSstring(reader, writingString, templateExpressions);
writingString = true;
continue;
}
}
appendCharacter((char) c, templateExpressions, writingString);
writingString = true;
}
if (writingString) {
templateExpressions.append("\"\"\"");
}
templateExpressions.append("}}");
// Use a new class loader by default for each class so each class can be independently garbage collected
final GroovyClassLoader loader = reuseClassLoader && parentLoader instanceof GroovyClassLoader?(GroovyClassLoader)parentLoader:(
(GroovyClassLoader) AccessController.doPrivileged(new PrivilegedAction() {
public Object run() {
return new GroovyClassLoader(parentLoader);
}
}));
final Class groovyClass;
try {
groovyClass = loader.parseClass(new GroovyCodeSource(templateExpressions.toString(), "GStringTemplateScript" + counter.incrementAndGet() + ".groovy", "x"));
} catch (Exception e) {
throw new GroovyRuntimeException("Failed to parse template script (your template may contain an error or be trying to use expressions not currently supported): " + e.getMessage());
}
try {
final GroovyObject script = (GroovyObject) groovyClass.newInstance();
this.template = (Closure) script.invokeMethod("getTemplate", null);
// GROOVY-6521: must set strategy to DELEGATE_FIRST, otherwise writing
// books = 'foo' in a template would store 'books' in the binding of the template script itself ("script")
// instead of storing it in the delegate, which is a Binding too
this.template.setResolveStrategy(Closure.DELEGATE_FIRST);
} catch (InstantiationException e) {
throw new ClassNotFoundException(e.getMessage());
} catch (IllegalAccessException e) {
throw new ClassNotFoundException(e.getMessage());
}
}
private static void appendCharacter(final char c,
final StringBuilder templateExpressions,
final boolean writingString) {
if (!writingString) {
templateExpressions.append("out << \"\"\"");
}
templateExpressions.append(c);
}
private void parseGSstring(Reader reader, boolean writingString, StringBuilder templateExpressions) throws IOException {
if (!writingString) {
templateExpressions.append("\"\"\"; ");
}
while (true) {
int c = reader.read();
if (c == -1) break;
templateExpressions.append((char) c);
if (c == '}') {
break;
}
}
}
/**
* Parse a <% .... %> section
* if we are writing a GString close and append ';'
* then write the section as a statement
*
* @param pendingC
* @param reader
* @param writingString
* @param templateExpressions
* @throws IOException
*/
private static void parseSection(final int pendingC,
final Reader reader,
final boolean writingString,
final StringBuilder templateExpressions)
throws IOException {
if (writingString) {
templateExpressions.append("\"\"\"; ");
}
templateExpressions.append((char) pendingC);
while (true) {
int c = reader.read();
if (c == -1) break;
if (c == '%') {
c = reader.read();
if (c == '>') break;
templateExpressions.append('%');
}
templateExpressions.append((char) c);
}
templateExpressions.append(";\n ");
}
/**
* Parse a <%= .... %> expression
*
* @param reader
* @param writingString
* @param templateExpressions
* @throws IOException
*/
private static void parseExpression(final Reader reader,
final boolean writingString,
final StringBuilder templateExpressions)
throws IOException {
if (!writingString) {
templateExpressions.append("out << \"\"\"");
}
templateExpressions.append("${");
while (true) {
int c = reader.read();
if (c == -1) break;
if (c == '%') {
c = reader.read();
if (c == '>') break;
templateExpressions.append('%');
}
templateExpressions.append((char) c);
}
templateExpressions.append('}');
}
public Writable make() {
return make(null);
}
public Writable make(final Map map) {
final Closure template = ((Closure) this.template.clone()).asWritable();
Binding binding = new Binding(map);
template.setDelegate(binding);
return (Writable) template;
}
}
}