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Groovy: A powerful, dynamic language for the JVM
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/*
 * 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.Binding;
import groovy.xml.MarkupBuilder;

import java.io.IOException;
import java.util.Enumeration;
import java.util.HashMap;
import java.util.Map;

import javax.servlet.ServletContext;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Servlet-specific binding extension to lazy load the writer or the output
 * stream from the response.
 * 
 * 
 * 
Default variables bound
 * 
 * "request" : the HttpServletRequest object
 * "response" : the HttpServletResponse object
 * "context" : the ServletContext object 
 * "application" : same as context
 * "session" : convenient for request.getSession(false) - can be null!
 * "params" : map of all form parameters - can be empty
 * "headers" : map of all request header fields
 * 
 * 
 * 
 * 
Implicite bound variables
 * 
 * "out" : response.getWriter() 
 * "sout" : response.getOutputStream() 
 * "html" : new MarkupBuilder(response.getWriter()) 
 * 
 * 
 * 
 * @author Guillaume Laforge
 * @author Christian Stein
 */
public class ServletBinding extends Binding {

    private final Binding binding;

    private final ServletContext context;

    private final HttpServletRequest request;

    private final HttpServletResponse response;

    private MarkupBuilder html;

    /**
     * Initializes a servlet binding.
     */
    public ServletBinding(HttpServletRequest request, HttpServletResponse response, ServletContext context) {
        this.binding = new Binding();
        this.request = request;
        this.response = response;
        this.context = context;

        /*
         * Bind the default variables.
         */
        binding.setVariable("request", request);
        binding.setVariable("response", response);
        binding.setVariable("context", context);
        binding.setVariable("application", context);

        /*
         * Bind the HTTP session object - if there is one.
         * Note: we don't create one here!
         */
        binding.setVariable("session", request.getSession(false));

        /*
         * Bind form parameter key-value hash map.
         *
         * If there are multiple, they are passed as an array.
         */
        Map params = new HashMap();
        for (Enumeration names = request.getParameterNames(); names.hasMoreElements();) {
            String name = (String) names.nextElement();
            if (!binding.getVariables().containsKey(name)) {
                String[] values = request.getParameterValues(name);
                if (values.length == 1) {
                    params.put(name, values[0]);
                } else {
                    params.put(name, values);
                }
            }
        }
        binding.setVariable("params", params);

        /*
         * Bind request header key-value hash map.
         */
        Map headers = new HashMap();
        for (Enumeration names = request.getHeaderNames(); names.hasMoreElements();) {
            String headerName = (String) names.nextElement();
            String headerValue = request.getHeader(headerName);
            headers.put(headerName, headerValue);
        }
        binding.setVariable("headers", headers);
    }

    public void setVariable(String name, Object value) {
        /*
         * Check sanity.
         */
        if (name == null) {
            throw new IllegalArgumentException("Can't bind variable to null key.");
        }
        if (name.length() == 0) {
            throw new IllegalArgumentException("Can't bind variable to blank key name. [length=0]");
        }
        /*
         * Check implicite key names. See getVariable(String)!
         */
        if ("out".equals(name)) {
            throw new IllegalArgumentException("Can't bind variable to key named '" + name + "'.");
        }
        if ("sout".equals(name)) {
            throw new IllegalArgumentException("Can't bind variable to key named '" + name + "'.");
        }
        if ("html".equals(name)) {
            throw new IllegalArgumentException("Can't bind variable to key named '" + name + "'.");
        }
        /*
         * TODO Check default key names. See constructor(s).
         */
        
        /*
         * All checks passed, set the variable.
         */
        binding.setVariable(name, value);
    }

    public Map getVariables() {
        return binding.getVariables();
    }

    /**
     * @return a writer, an output stream, a markup builder or another requested object
     */
    public Object getVariable(String name) {
        /*
         * Check sanity.
         */
        if (name == null) {
            throw new IllegalArgumentException("No variable with null key name.");
        }
        if (name.length() == 0) {
            throw new IllegalArgumentException("No variable with blank key name. [length=0]");
        }
        /*
         * Check implicite key names. See setVariable(String, Object)!
         */
        try {
            if ("out".equals(name)) {
                return response.getWriter();
            }
            if ("sout".equals(name)) {
                return response.getOutputStream();
            }
            if ("html".equals(name)) {
                if (html == null) {
                    html = new MarkupBuilder(response.getWriter());
                }
                return html;
            }
        } catch (IOException e) {
            String message = "Failed to get writer or output stream from response.";
            context.log(message, e);
            throw new RuntimeException(message, e);
        }
        /*
         * Still here? Delegate to the binding object.
         */
        return binding.getVariable(name);
    }
}