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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.BufferedReader;
import java.io.IOException;
import java.io.PrintWriter;
import java.io.Reader;
import java.io.StringWriter;
import java.io.Writer;
import java.util.Map;
import org.codehaus.groovy.control.CompilationFailedException;
import org.codehaus.groovy.runtime.InvokerHelper;
/**
* Processes template source files substituting variables and expressions into
* placeholders in a template source text to produce the desired output.
*
* 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.SimpleTemplateEngine()
* 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>SimpleTemplate</servlet-name>
* <servlet-class>groovy.servlet.TemplateServlet</servlet-class>
* <init-param>
* <param-name>template.engine</param-name>
* <param-value>groovy.text.SimpleTemplateEngine</param-value>
* </init-param>
* </servlet>
*
* In this case, your template source file should be HTML with the appropriate embedded placeholders.
*
* @author sam
* @author Christian Stein
* @author Paul King
* @author Alex Tkachman
*/
public class SimpleTemplateEngine extends TemplateEngine {
private boolean verbose;
private static int counter = 1;
private GroovyShell groovyShell;
public SimpleTemplateEngine() {
this(GroovyShell.class.getClassLoader());
}
public SimpleTemplateEngine(boolean verbose) {
this(GroovyShell.class.getClassLoader());
setVerbose(verbose);
}
public SimpleTemplateEngine(ClassLoader parentLoader) {
this(new GroovyShell(parentLoader));
}
public SimpleTemplateEngine(GroovyShell groovyShell) {
this.groovyShell = groovyShell;
}
public Template createTemplate(Reader reader) throws CompilationFailedException, IOException {
SimpleTemplate template = new SimpleTemplate();
String script = template.parse(reader);
if (verbose) {
System.out.println("\n-- script source --");
System.out.print(script);
System.out.println("\n-- script end --\n");
}
try {
template.script = groovyShell.parse(script, "SimpleTemplateScript" + counter++ + ".groovy");
} 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());
}
return template;
}
/**
* @param verbose true if you want the engine to display the template source file for debugging purposes
*/
public void setVerbose(boolean verbose) {
this.verbose = verbose;
}
public boolean isVerbose() {
return verbose;
}
private static class SimpleTemplate implements Template {
protected Script script;
public Writable make() {
return make(null);
}
public Writable make(final Map map) {
return new Writable() {
/**
* Write the template document with the set binding applied to the writer.
*
* @see groovy.lang.Writable#writeTo(java.io.Writer)
*/
public Writer writeTo(Writer writer) {
Binding binding;
if (map == null)
binding = new Binding();
else
binding = new Binding(map);
Script scriptObject = InvokerHelper.createScript(script.getClass(), binding);
PrintWriter pw = new PrintWriter(writer);
scriptObject.setProperty("out", pw);
scriptObject.run();
pw.flush();
return writer;
}
/**
* Convert the template and binding into a result String.
*
* @see java.lang.Object#toString()
*/
public String toString() {
StringWriter sw = new StringWriter();
writeTo(sw);
return sw.toString();
}
};
}
/**
* Parse the text document looking for <% or <%= and then call out to the appropriate handler, otherwise copy the text directly
* into the script while escaping quotes.
*
* @param reader a reader for the template text
* @return the parsed text
* @throws IOException if something goes wrong
*/
protected String parse(Reader reader) throws IOException {
if (!reader.markSupported()) {
reader = new BufferedReader(reader);
}
StringWriter sw = new StringWriter();
startScript(sw);
int c;
while ((c = reader.read()) != -1) {
if (c == '<') {
reader.mark(1);
c = reader.read();
if (c != '%') {
sw.write('<');
reader.reset();
} else {
reader.mark(1);
c = reader.read();
if (c == '=') {
groovyExpression(reader, sw);
} else {
reader.reset();
groovySection(reader, sw);
}
}
continue; // at least '<' is consumed ... read next chars.
}
if (c == '$') {
reader.mark(1);
c = reader.read();
if (c != '{') {
sw.write('$');
reader.reset();
} else {
reader.mark(1);
sw.write("${");
processGSstring(reader, sw);
}
continue; // at least '$' is consumed ... read next chars.
}
if (c == '\"') {
sw.write('\\');
}
/*
* Handle raw new line characters.
*/
if (c == '\n' || c == '\r') {
if (c == '\r') { // on Windows, "\r\n" is a new line.
reader.mark(1);
c = reader.read();
if (c != '\n') {
reader.reset();
}
}
sw.write("\n");
continue;
}
sw.write(c);
}
endScript(sw);
return sw.toString();
}
private void startScript(StringWriter sw) {
sw.write("out.print(\"\"\"");
}
private void endScript(StringWriter sw) {
sw.write("\"\"\");\n");
sw.write("\n/* Generated by SimpleTemplateEngine */");
}
private void processGSstring(Reader reader, StringWriter sw) throws IOException {
int c;
while ((c = reader.read()) != -1) {
if (c != '\n' && c != '\r') {
sw.write(c);
}
if (c == '}') {
break;
}
}
}
/**
* Closes the currently open write and writes out the following text as a GString expression until it reaches an end %>.
*
* @param reader a reader for the template text
* @param sw a StringWriter to write expression content
* @throws IOException if something goes wrong
*/
private void groovyExpression(Reader reader, StringWriter sw) throws IOException {
sw.write("${");
int c;
while ((c = reader.read()) != -1) {
if (c == '%') {
c = reader.read();
if (c != '>') {
sw.write('%');
} else {
break;
}
}
if (c != '\n' && c != '\r') {
sw.write(c);
}
}
sw.write("}");
}
/**
* Closes the currently open write and writes the following text as normal Groovy script code until it reaches an end %>.
*
* @param reader a reader for the template text
* @param sw a StringWriter to write expression content
* @throws IOException if something goes wrong
*/
private void groovySection(Reader reader, StringWriter sw) throws IOException {
sw.write("\"\"\");");
int c;
while ((c = reader.read()) != -1) {
if (c == '%') {
c = reader.read();
if (c != '>') {
sw.write('%');
} else {
break;
}
}
/* Don't eat EOL chars in sections - as they are valid instruction separators.
* See https://issues.apache.org/jira/browse/GROOVY-980
*/
// if (c != '\n' && c != '\r') {
sw.write(c);
//}
}
sw.write(";\nout.print(\"\"\"");
}
}
}