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Groovy example source code file (XmlTemplateEngine.java)

This example Groovy source code file (XmlTemplateEngine.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java - Groovy tags/keywords

groovyshell, groovyshell, gspprinter, gspprinter, io, parser, printwriter, sax, saxexception, script, string, string, util, weakreference, writable, xml, xmltemplate, xmltemplateengine, xmltemplateengine

The Groovy XmlTemplateEngine.java source code

/*
 * Copyright 2003-2009 the original author or authors.
 *
 * Licensed 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.Binding;
import groovy.lang.GroovyRuntimeException;
import groovy.lang.GroovyShell;
import groovy.lang.Script;
import groovy.lang.Writable;
import groovy.util.IndentPrinter;
import groovy.util.Node;
import groovy.util.XmlNodePrinter;
import groovy.util.XmlParser;
import groovy.xml.QName;
import org.codehaus.groovy.control.CompilationFailedException;
import org.codehaus.groovy.runtime.InvokerHelper;
import org.xml.sax.SAXException;

import javax.xml.parsers.ParserConfigurationException;
import java.io.IOException;
import java.io.PrintWriter;
import java.io.Reader;
import java.io.StringWriter;
import java.io.Writer;
import java.lang.ref.WeakReference;
import java.util.HashMap;
import java.util.Map;

/**
 * Template engine for use in templating scenarios where both the template
 * source and the expected output are intended to be XML.
 * </p>
 * Templates may use the normal '${expression}' and '$variable' notations
 * to insert an arbitrary expression into the template.
 * In addition, support is also provided for special tags:
 * <gsp:scriptlet> (for inserting code fragments) and
 * <gsp:expression> (for code fragments which produce output).
 * </p>
 * Comments and processing instructions
 * will be removed as part of processing and special XML characters such as
 * <, >, " and ' will be escaped using the respective XML notation.
 * The output will also be indented using standard XML pretty printing.
 * </p>
 * The xmlns namespace definition for <code>gsp: tags will be removed
 * but other namespace definitions will be preserved (but may change to an
 * equivalent position within the XML tree).
 * </p>
 * Normally, the template source will be in a file but here is a simple
 * example providing the XML template as a string:
 * <pre>
 * def binding = [firstname:"Jochen", lastname:"Theodorou",
 *                nickname:"blackdrag", salutation:"Dear"]
 * def engine = new groovy.text.XmlTemplateEngine()
 * def text = '''\
 * <?xml version="1.0" encoding="UTF-8"?>
 * <document xmlns:gsp='http://groovy.codehaus.org/2005/gsp' xmlns:foo='baz' type='letter'>
 *   <gsp:scriptlet>def greeting = "${salutation}est"</gsp:scriptlet>
 *   <gsp:expression>greeting</gsp:expression>
 *   <foo:to>$firstname "$nickname" $lastname</foo:to>
 *   How are you today?
 * </document>
 * '''
 * def template = engine.createTemplate(text).make(binding)
 * println template.toString()
 * </pre>
 * This example will produce this output:
 * <pre>
 * <document type='letter'>
 * Dearest
 * <foo:to xmlns:foo='baz'>
 *   Jochen &quot;blackdrag&quot; Theodorou
 * </foo:to>
 * How are you today?
 * </document>
 * </pre>
 * The XML 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):
 * <pre>
 * <servlet>
 *   <servlet-name>XmlTemplate</servlet-name>
 *   <servlet-class>groovy.servlet.TemplateServlet</servlet-class>
 *   <init-param>
 *     <param-name>template.engine</param-name>
 *     <param-value>groovy.text.XmlTemplateEngine</param-value>
 *   </init-param>
 * </servlet>
 * </pre>
 *
 * @author Christian Stein
 * @author Paul King
 */
public class XmlTemplateEngine extends TemplateEngine {

    private static int counter = 1;

    private static class GspPrinter extends XmlNodePrinter {

        public GspPrinter(PrintWriter out, String indent) {
            this(new IndentPrinter(out, indent));
        }

        public GspPrinter(IndentPrinter out) {
            super(out, "\\\"");
            setQuote("'");
        }

        protected void printGroovyTag(String tag, String text) {
            if (tag.equals("scriptlet")) {
                out.print(text);
                out.print("\n");
                return;
            }
            if (tag.equals("expression")) {
                printLineBegin();
                out.print("${");
                out.print(text);
                out.print("}");
                printLineEnd();
                return;
            }
            throw new RuntimeException("Unsupported 'gsp:' tag named \"" + tag + "\".");
        }

        protected void printSimpleItem(Object value) {
            this.printLineBegin();
            out.print(escapeSpecialChars(InvokerHelper.toString(value)));
            printLineEnd();
        }

        private String escapeSpecialChars(String s) {
            StringBuilder sb = new StringBuilder();
            boolean inGString = false;
            for (int i = 0; i < s.length(); i++) {
                final char c = s.charAt(i);
                switch (c) {
                    case '$':
                        sb.append("$");
                        if (i < s.length() - 1 && s.charAt(i + 1) == '{') inGString = true;
                        break;
                    case '<':
                        append(sb, c, "<", inGString);
                        break;
                    case '>':
                        append(sb, c, ">", inGString);
                        break;
                    case '"':
                        append(sb, c, """, inGString);
                        break;
                    case '\'':
                        append(sb, c, "'", inGString);
                        break;
                    case '}':
                        sb.append(c);
                        inGString = false;
                        break;
                    default:
                        sb.append(c);
                }
            }
            return sb.toString();
        }

        private void append(StringBuilder sb, char plainChar, String xmlString, boolean inGString) {
            if (inGString) {
                sb.append(plainChar);
            } else {
                sb.append(xmlString);
            }
        }

        protected void printLineBegin() {
            out.print("out.print(\"\"\"");
            out.printIndent();
        }

        protected void printLineEnd(String comment) {
            out.print("\\n\"\"\");");
            if (comment != null) {
                out.print(" // ");
                out.print(comment);
            }
            out.print("\n");
        }

        protected boolean printSpecialNode(Node node) {
            Object name = node.name();
            if (name != null && name instanceof QName) {
                QName qn = (QName) name;
                // check uri and for legacy cases just check prefix name (not recommended)
                if (qn.getNamespaceURI().equals("http://groovy.codehaus.org/2005/gsp") || qn.getPrefix().equals("gsp")) {
                    String s = qn.getLocalPart();
                    if (s.length() == 0) {
                        throw new RuntimeException("No local part after 'gsp:' given in node " + node);
                    }
                    printGroovyTag(s, node.text());
                    return true;
                }
            }
            return false;
        }
    }

    private static class XmlTemplate implements Template {

        private final Script script;

        public XmlTemplate(Script script) {
            this.script = script;
        }

        public Writable make() {
            return make(new HashMap());
        }

        public Writable make(Map map) {
            if (map == null) {
                throw new IllegalArgumentException("map must not be null");
            }
            return new XmlWritable(script, new Binding(map));
        }
    }

    private static class XmlWritable implements Writable {

        private final Binding binding;
        private final Script script;
        private WeakReference result;

        public XmlWritable(Script script, Binding binding) {
            this.script = script;
            this.binding = binding;
            this.result = new WeakReference(null);
        }

        public Writer writeTo(Writer out) {
            Script scriptObject = InvokerHelper.createScript(script.getClass(), binding);
            PrintWriter pw = new PrintWriter(out);
            scriptObject.setProperty("out", pw);
            scriptObject.run();
            pw.flush();
            return out;
        }

        public String toString() {
            if (result.get() != null) {
                return result.get().toString();
            }
            String string = writeTo(new StringWriter(1024)).toString();
            result = new WeakReference(string);
            return string;
        }
    }

    public static final String DEFAULT_INDENTATION = "  ";

    private final GroovyShell groovyShell;
    private final XmlParser xmlParser;
    private String indentation;

    public XmlTemplateEngine() throws SAXException, ParserConfigurationException {
        this(DEFAULT_INDENTATION, false);
    }

    public XmlTemplateEngine(String indentation, boolean validating) throws SAXException, ParserConfigurationException {
        this(new XmlParser(validating, true), new GroovyShell());
        setIndentation(indentation);
    }

    public XmlTemplateEngine(XmlParser xmlParser, ClassLoader parentLoader) {
        this(xmlParser, new GroovyShell(parentLoader));
    }

    public XmlTemplateEngine(XmlParser xmlParser, GroovyShell groovyShell) {
        this.groovyShell = groovyShell;
        this.xmlParser = xmlParser;
        setIndentation(DEFAULT_INDENTATION);
    }

    public Template createTemplate(Reader reader) throws CompilationFailedException, ClassNotFoundException, IOException {
        Node root ;
        try {
            root = xmlParser.parse(reader);
        } catch (SAXException e) {
            throw new RuntimeException("Parsing XML source failed.", e);
        }

        if (root == null) {
            throw new IOException("Parsing XML source failed: root node is null.");
        }

        StringWriter writer = new StringWriter(1024);
        writer.write("/* Generated by XmlTemplateEngine */\n");
        new GspPrinter(new PrintWriter(writer), indentation).print(root);

        Script script;
        try {
            script = groovyShell.parse(writer.toString(), "XmlTemplateScript" + 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 new XmlTemplate(script);
    }

    public String getIndentation() {
        return indentation;
    }

    public void setIndentation(String indentation) {
        if (indentation == null) {
            indentation = DEFAULT_INDENTATION;
        }
        this.indentation = indentation;
    }

    public String toString() {
        return "XmlTemplateEngine";
    }

}

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