groovy-core/src/main/groovy/text/SimpleTemplateEngine.java

/*
 * $Id$
 *
 * Copyright 2003-2007 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.GroovyShell;
import groovy.lang.Script;
import groovy.lang.Writable;

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;

/**
 * This simple template engine uses JSP <% %> script and <%= %> expression syntax.  It also lets you use normal groovy expressions in
 * the template text much like the new JSP EL functionality.  The variable 'out' is bound to the writer that the template is being written to.
 *
 * @author sam
 * @author Christian Stein
 */
public class SimpleTemplateEngine extends TemplateEngine {

    private final boolean verbose;

    public SimpleTemplateEngine() {
        this(false);
    }

    public SimpleTemplateEngine(boolean verbose) {
        this.verbose = verbose;
    }

    public Template createTemplate(Reader reader) throws CompilationFailedException, IOException {
        return createTemplate(GroovyShell.class.getClassLoader(), reader);
    }

    public Template createTemplate(ClassLoader parentLoader, Reader reader)
            throws CompilationFailedException, IOException {
        SimpleTemplate template = new SimpleTemplate();
        GroovyShell shell = new GroovyShell(parentLoader);
        String script = template.parse(reader);
        if (verbose) {
            System.out.println("\n-- script source --");
            System.out.print(script);
            System.out.println("\n-- script end --\n");
        }
        template.script = shell.parse(script);
        return template;
    }

    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() {
                    try {
                        StringWriter sw = new StringWriter();
                        writeTo(sw);
                        return sw.toString();
                    } catch (Exception e) {
                        return e.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
         * @throws IOException if something goes wrong
         * @return the parsed text
         */
        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 == '\"') {
                    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\");\nout.print(\"");
                    continue;
                }
                sw.write(c);
            }
            endScript(sw);
            return sw.toString();
        }

        private void startScript(StringWriter sw) {
            sw.write("/* Generated by SimpleTemplateEngine */\n");
            sw.write("out.print(\"");
        }

        private void endScript(StringWriter sw) {
            sw.write("\");\n");
        }

        /**
         * 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("\");out.print(\"${");
            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("}\");\nout.print(\"");
        }

        /**
         * 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 http://jira.codehaus.org/browse/GROOVY-980
                 */
                // if (c != '\n' && c != '\r') {
                sw.write(c);
                //}
            }
            sw.write(";\nout.print(\"");
        }

    }
}