ParamTag.java

/*
 * Copyright 1999-2004 The Apache Software Foundation.
 *
 * 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 org.anodyneos.xp.tag.core;

import java.io.UnsupportedEncodingException;
import java.net.URLEncoder;
import java.util.LinkedList;
import java.util.List;

import javax.servlet.jsp.el.ELException;

import org.anodyneos.xp.XpException;
import org.anodyneos.xp.XpOutput;
import org.anodyneos.xp.tagext.XpTag;
import org.anodyneos.xp.tagext.XpTagSupport;
import org.xml.sax.SAXException;

/**
 * <p>
 * Support for tag handlers for <param>, the URL parameter subtag for
 * <import> in JSTL 1.0.
 * </p>
 *
 * @see ParamParent, ImportSupport, URLEncodeSupport
 * @author Shawn Bayern
 */

public class ParamTag extends XpTagSupport {

    // *********************************************************************
    // Protected state

    protected String name; // 'name' attribute

    protected String value; // 'value' attribute

    // *********************************************************************
    // Constructor and initialization

    public ParamTag() {
        name = value = null;
    }

    // *********************************************************************
    // Tag logic

    // simply send our name and value to our appropriate ancestor
    public void doTag(XpOutput out) throws XpException, SAXException,
            ELException {
        XpTag t = findAncestorWithClass(this, ParamParent.class);
        if (t == null) {
            throw new XpException("No ParamParent found.");
        }

        // take no action for null or empty names
        if (name == null || name.equals("")) {
            return;
        }

        // send the parameter to the appropriate ancestor
        ParamParent parent = (ParamParent) t;
        String value = this.value;
        if (value == null) {
            if (getXpBody() == null) {
                value = "";
            } else {
                value = getXpBody().invokeToString().trim();
            }
        }

        parent.addParameter(name, value);

    }

    // for tag attribute
    public void setName(String name) {
        this.name = name;
    }

    // for tag attribute
    public void setValue(String value) {
        this.value = value;
    }

    // *********************************************************************
    // Support for parameter management

    /**
     * Provides support for aggregating query parameters in URLs. Specifically,
     * accepts a series of parameters, ensuring that - newer parameters will
     * precede older ones in the output URL - all supplied parameters precede
     * those in the input URL
     */
    public static class ParamManager {

        // *********************************
        // Private state

        private List names = new LinkedList();

        private List values = new LinkedList();

        private boolean done = false;

        // *********************************
        // Public interface

        /** Adds a new parameter to the list. */
        public void addParameter(String name, String value) {
            if (done)
                throw new IllegalStateException();
            if (name != null) {
                names.add(name);
                if (value != null)
                    values.add(value);
                else
                    values.add("");
            }
        }

        /**
         * Produces a new URL with the stored parameters, in the appropriate
         * order.
         */
        public String aggregateParams(String url, String fragment, String encoding)
        throws UnsupportedEncodingException {
            if (done) {
                throw new IllegalStateException();
            }
            done = true;

            if (names.isEmpty() && (null == fragment)) {
                return url;
            }

            int poundIndex = url.indexOf('#');
            int questionMarkIndex = url.indexOf('?');

            if (questionMarkIndex > poundIndex) {
                questionMarkIndex = -1;
            }

            // fragment
            String workingFragment = null;
            if (null != fragment) {
                workingFragment = URLEncoder.encode(fragment, encoding);
            } else if (-1 != poundIndex) {
                workingFragment = url.substring(poundIndex + 1);
            }

            // oldQuery
            String oldQuery = null;
            if (-1 != questionMarkIndex) {
                if (-1 == poundIndex) {
                    oldQuery = url.substring(questionMarkIndex + 1);
                } else {
                    oldQuery = url.substring(questionMarkIndex + 1, poundIndex);
                }
            }

            // build the URL
            StringBuilder workingUrl = new StringBuilder();

            // base
            if (-1 == poundIndex && -1 == questionMarkIndex) {
                workingUrl.append(url);
            } else if (-1 != questionMarkIndex) {
                workingUrl.append(url.substring(0, questionMarkIndex));
            } else if (-1 != poundIndex) {
                workingUrl.append(url.substring(0, poundIndex));
            }

            // newQuery
            boolean queryStarted = false;
            if (! names.isEmpty()) {
                workingUrl.append('?');
                queryStarted = true;
                for (int i = 0; i < names.size(); i++) {
                    workingUrl.append(URLEncoder.encode((String) names.get(i), encoding));
                    workingUrl.append('=');
                    workingUrl.append(URLEncoder.encode((String) values.get(i), encoding));
                    if (i < (names.size() - 1)) {
                        workingUrl.append("&");
                    }
                }
            }

            // old query params
            if (null != oldQuery && oldQuery.length() > 0) {
                if (! queryStarted) {
                    workingUrl.append('?');
                } else {
                    workingUrl.append('&');
                }
                workingUrl.append(oldQuery);
            }

            // fragment
            if (null != workingFragment && workingFragment.length() > 0) {
                workingUrl.append("#");
                workingUrl.append(workingFragment);
            }

            return workingUrl.toString();
        }
    }
}