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Groovy example source code file (GroovyServlet.java)

This example Groovy source code file (GroovyServlet.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

closure, closure, groovy, groovyscriptengine, groovyscriptengine, groovyservlet, groovyservlet, http, io, ioexception, request, resourceexception, response, runtimeexception, runtimeexception, script, servlet, servletbinding, stringbuffer

The Groovy GroovyServlet.java source code

/*
 * 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.servlet;

import groovy.lang.Closure;
import groovy.util.GroovyScriptEngine;
import groovy.util.ResourceException;
import groovy.util.ScriptException;

import java.io.IOException;

import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.codehaus.groovy.runtime.GroovyCategorySupport;

/**
 * This servlet will run Groovy scripts as Groovlets.  Groovlets are scripts
 * with these objects implicit in their scope:
 *
 * <ul>
 *  <li>request - the HttpServletRequest
 *  <li>response - the HttpServletResponse
 *  <li>application - the ServletContext associated with the servlet
 *  <li>session - the HttpSession associated with the HttpServletRequest
 *  <li>out - the PrintWriter associated with the ServletRequest
 * </ul>
 *
 * <p>Your script sources can be placed either in your web application's normal
 * web root (allows for subdirectories) or in /WEB-INF/groovy/* (also allows
 * subdirectories).
 *
 * <p>To make your web application more groovy, you must add the GroovyServlet
 * to your application's web.xml configuration using any mapping you like, so
 * long as it follows the pattern *.* (more on this below).  Here is the
 * web.xml entry:
 *
 * <pre>
 *    <servlet>
 *      <servlet-name>Groovy</servlet-name>
 *      <servlet-class>groovy.servlet.GroovyServlet</servlet-class>
 *    </servlet>
 *
 *    <servlet-mapping>
 *      <servlet-name>Groovy</servlet-name>
 *      <url-pattern>*.groovy</url-pattern>
 *      <url-pattern>*.gdo</url-pattern>
 *    </servlet-mapping>
 * </pre>
 *
 * <p>The URL pattern does not require the "*.groovy" mapping.  You can, for
 * example, make it more Struts-like but groovy by making your mapping "*.gdo".
 *
 * @author Sam Pullara
 * @author Mark Turansky (markturansky at hotmail.com)
 * @author Guillaume Laforge
 * @author Christian Stein
 * @author Marcel Overdijk
 *
 * @see groovy.servlet.ServletBinding
 */
public class GroovyServlet extends AbstractHttpServlet {

    /**
     * The script engine executing the Groovy scripts for this servlet
     */
    private GroovyScriptEngine gse;

    /**
     * Initialize the GroovyServlet.
     *
     * @throws ServletException
     *  if this method encountered difficulties
     */
    public void init(ServletConfig config) throws ServletException {
        super.init(config);

        // Set up the scripting engine
        gse = createGroovyScriptEngine();

        servletContext.log("Groovy servlet initialized on " + gse + ".");
    }

    /**
     * Handle web requests to the GroovyServlet
     */
    public void service(HttpServletRequest request, HttpServletResponse response) throws IOException {

        // Get the script path from the request - include aware (GROOVY-815)
        final String scriptUri = getScriptUri(request);

        // Set it to HTML by default
        response.setContentType("text/html; charset="+encoding);

        // Set up the script context
        final ServletBinding binding = new ServletBinding(request, response, servletContext);
        setVariables(binding);

        // Run the script
        try {
            Closure closure = new Closure(gse) {

                public Object call() {
                    try {
                        return ((GroovyScriptEngine) getDelegate()).run(scriptUri, binding);
                    } catch (ResourceException e) {
                        throw new RuntimeException(e);
                    } catch (ScriptException e) {
                        throw new RuntimeException(e);
                    }
                }

            };
            GroovyCategorySupport.use(ServletCategory.class, closure);
        } catch (RuntimeException runtimeException) {
            StringBuffer error = new StringBuffer("GroovyServlet Error: ");
            error.append(" script: '");
            error.append(scriptUri);
            error.append("': ");
            Throwable e = runtimeException.getCause();
            /*
             * Null cause?!
             */
            if (e == null) {
                error.append(" Script processing failed.");
                error.append(runtimeException.getMessage());
                if (runtimeException.getStackTrace().length > 0)
                    error.append(runtimeException.getStackTrace()[0].toString());
                servletContext.log(error.toString());
                System.err.println(error.toString());
                runtimeException.printStackTrace(System.err);
                response.sendError(HttpServletResponse.SC_INTERNAL_SERVER_ERROR, error.toString());
                return;
            }
            /*
             * Resource not found.
             */
            if (e instanceof ResourceException) {
                error.append(" Script not found, sending 404.");
                servletContext.log(error.toString());
                System.err.println(error.toString());
                response.sendError(HttpServletResponse.SC_NOT_FOUND);
                return;
            }
            /*
             * Other internal error. Perhaps syntax?!
             */
            servletContext.log("An error occurred processing the request", runtimeException);
            error.append(e.getMessage());
            if (e.getStackTrace().length > 0)
                error.append(e.getStackTrace()[0].toString());
            servletContext.log(e.toString());
            System.err.println(e.toString());
            runtimeException.printStackTrace(System.err);
            response.sendError(HttpServletResponse.SC_INTERNAL_SERVER_ERROR, e.toString());
        }
    }

    /**
     * Hook method to setup the GroovyScriptEngine to use.<br/>
     * Subclasses may override this method to provide a custom
     * engine.
     */
    protected GroovyScriptEngine createGroovyScriptEngine(){
        return new GroovyScriptEngine(this);
    }
}

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