Ant example source code file (PropertyHelper.java)

This example Ant source code file (PropertyHelper.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 - Ant tags/keywords

buildexception, enumeration, hashtable, hashtable, object, object, override, propertyhelper, propertyhelper, setting, string, string, stringbuffer, util, vector

The PropertyHelper.java source code

/*
 *  Licensed to the Apache Software Foundation (ASF) under one or more
 *  contributor license agreements.  See the NOTICE file distributed with
 *  this work for additional information regarding copyright ownership.
 *  The ASF licenses this file to You 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.apache.tools.ant;

import java.util.Hashtable;
import java.util.Vector;
import java.util.Enumeration;


/* ISSUES:
 - ns param. It could be used to provide "namespaces" for properties, which
 may be more flexible.
 - Object value. In ant1.5 String is used for Properties - but it would be nice
 to support generic Objects (the property remains immutable - you can't change
 the associated object). This will also allow JSP-EL style setting using the
 Object if an attribute contains only the property (name="${property}" could
 avoid Object->String->Object conversion)
 - Currently we "chain" only for get and set property (probably most users
 will only need that - if they need more they can replace the top helper).
 Need to discuss this and find if we need more.
 */

/** NOT FINAL. API MAY CHANGE
 *
 * Deals with properties - substitution, dynamic properties, etc.
 *
 * This is the same code as in Ant1.5. The main addition is the ability
 * to chain multiple PropertyHelpers and to replace the default.
 *
 * @since Ant 1.6
 */
public class PropertyHelper {

    private Project project;
    private PropertyHelper next;

    /** Project properties map (usually String to String). */
    private Hashtable properties = new Hashtable();

    /**
     * Map of "user" properties (as created in the Ant task, for example).
     * Note that these key/value pairs are also always put into the
     * project properties, so only the project properties need to be queried.
     * Mapping is String to String.
     */
    private Hashtable userProperties = new Hashtable();

    /**
     * Map of inherited "user" properties - that are those "user"
     * properties that have been created by tasks and not been set
     * from the command line or a GUI tool.
     * Mapping is String to String.
     */
    private Hashtable inheritedProperties = new Hashtable();

    /**
     * Default constructor.
     */
    protected PropertyHelper() {
    }

    //override facility for subclasses to put custom hashtables in


    // --------------------  Hook management  --------------------

    /**
     * Set the project for which this helper is performing property resolution
     *
     * @param p the project instance.
     */
    public void setProject(Project p) {
        this.project = p;
    }

    /** There are 2 ways to hook into property handling:
     *  - you can replace the main PropertyHelper. The replacement is required
     * to support the same semantics (of course :-)
     *
     *  - you can chain a property helper capable of storing some properties.
     *  Again, you are required to respect the immutability semantics (at
     *  least for non-dynamic properties)
     *
     * @param next the next property helper in the chain.
     */
    public void setNext(PropertyHelper next) {
        this.next = next;
    }

    /**
     * Get the next property helper in the chain.
     *
     * @return the next property helper.
     */
    public PropertyHelper getNext() {
        return next;
    }

    /**
     * Factory method to create a property processor.
     * Users can provide their own or replace it using "ant.PropertyHelper"
     * reference. User tasks can also add themselves to the chain, and provide
     * dynamic properties.
     *
     * @param project the project fro which the property helper is required.
     *
     * @return the project's property helper.
     */
    public static synchronized
        PropertyHelper getPropertyHelper(Project project) {
        PropertyHelper helper
            = (PropertyHelper) project.getReference(MagicNames.REFID_PROPERTY_HELPER);
        if (helper != null) {
            return helper;
        }
        helper = new PropertyHelper();
        helper.setProject(project);

        project.addReference(MagicNames.REFID_PROPERTY_HELPER, helper);
        return helper;
    }

    // --------------------  Methods to override  --------------------

    /**
     * Sets a property. Any existing property of the same name
     * is overwritten, unless it is a user property. Will be called
     * from setProperty().
     *
     * If all helpers return false, the property will be saved in
     * the default properties table by setProperty.
     *
     * @param ns   The namespace that the property is in (currently
     *             not used.
     * @param name The name of property to set.
     *             Must not be <code>null.
     * @param value The new value of the property.
     *              Must not be <code>null.
     * @param inherited True if this property is inherited (an [sub]ant[call] property).
     * @param user      True if this property is a user property.
     * @param isNew     True is this is a new property.
     * @return true if this helper has stored the property, false if it
     *    couldn't. Each helper should delegate to the next one (unless it
     *    has a good reason not to).
     */
    public boolean setPropertyHook(String ns, String name,
                                   Object value,
                                   boolean inherited, boolean user,
                                   boolean isNew) {
        if (getNext() != null) {
            boolean subst = getNext().setPropertyHook(ns, name, value,
                    inherited, user, isNew);
            // If next has handled the property
            if (subst) {
                return true;
            }
        }
        return false;
    }

    /** Get a property. If all hooks return null, the default
     * tables will be used.
     *
     * @param ns namespace of the sought property.
     * @param name name of the sought property.
     * @param user True if this is a user property.
     * @return The property, if returned by a hook, or null if none.
     */
    public Object getPropertyHook(String ns, String name, boolean user) {
        if (getNext() != null) {
            Object o = getNext().getPropertyHook(ns, name, user);
            if (o != null) {
                return o;
            }
        }
        // Experimental/Testing, will be removed
        if (name.startsWith("toString:")) {
            name = name.substring("toString:".length());
            Object v = project.getReference(name);
            return (v == null) ? null : v.toString();
        }
        return null;
    }

    // -------------------- Optional methods   --------------------
    // You can override those methods if you want to optimize or
    // do advanced things (like support a special syntax).
    // The methods do not chain - you should use them when embedding ant
    // (by replacing the main helper)

    /**
     * Parses a string containing <code>${xxx} style property
     * references into two lists. The first list is a collection
     * of text fragments, while the other is a set of string property names.
     * <code>null entries in the first list indicate a property
     * reference from the second list.
     *
     * It can be overridden with a more efficient or customized version.
     *
     * @param value     Text to parse. Must not be <code>null.
     * @param fragments List to add text fragments to.
     *                  Must not be <code>null.
     * @param propertyRefs List to add property names to.
     *                     Must not be <code>null.
     *
     * @exception BuildException if the string contains an opening
     *                           <code>${ without a closing
     *                           <code>}
     */
    public void parsePropertyString(String value, Vector fragments,
                                    Vector propertyRefs)
        throws BuildException {
        parsePropertyStringDefault(value, fragments, propertyRefs);
    }

    /**
     * Replaces <code>${xxx} style constructions in the given value
     * with the string value of the corresponding data types.
     *
     * @param ns    The namespace for the property.
     * @param value The string to be scanned for property references.
     *              May be <code>null, in which case this
     *              method returns immediately with no effect.
     * @param keys  Mapping (String to String) of property names to their
     *              values. If <code>null, only project properties will
     *              be used.
     *
     * @exception BuildException if the string contains an opening
     *                           <code>${ without a closing
     *                           <code>}
     * @return the original string with the properties replaced, or
     *         <code>null if the original string is null.
     */
    public String replaceProperties(String ns, String value, Hashtable keys)
            throws BuildException {
        if (value == null || value.indexOf('$') == -1) {
            return value;
        }
        Vector fragments = new Vector();
        Vector propertyRefs = new Vector();
        parsePropertyString(value, fragments, propertyRefs);

        StringBuffer sb = new StringBuffer();
        Enumeration i = fragments.elements();
        Enumeration j = propertyRefs.elements();

        while (i.hasMoreElements()) {
            String fragment = (String) i.nextElement();
            if (fragment == null) {
                String propertyName = (String) j.nextElement();
                Object replacement = null;

                // try to get it from the project or keys
                // Backward compatibility
                if (keys != null) {
                    replacement = keys.get(propertyName);
                }
                if (replacement == null) {
                    replacement = getProperty(ns, propertyName);
                }

                if (replacement == null) {
                    project.log("Property \"" + propertyName
                            + "\" has not been set", Project.MSG_VERBOSE);
                }
                fragment = (replacement != null)
                        ? replacement.toString()
                        : "${" + propertyName + "}";
            }
            sb.append(fragment);
        }
        return sb.toString();
    }

    // -------------------- Default implementation  --------------------
    // Methods used to support the default behavior and provide backward
    // compatibility. Some will be deprecated, you should avoid calling them.


    /** Default implementation of setProperty. Will be called from Project.
     *  This is the original 1.5 implementation, with calls to the hook
     *  added.
     *  @param ns      The namespace for the property (currently not used).
     *  @param name    The name of the property.
     *  @param value   The value to set the property to.
     *  @param verbose If this is true output extra log messages.
     *  @return true if the property is set.
     */
    public synchronized boolean setProperty(String ns, String name,
                                            Object value, boolean verbose) {
        // user (CLI) properties take precedence
        if (null != userProperties.get(name)) {
            if (verbose) {
                project.log("Override ignored for user property \"" + name
                    + "\"", Project.MSG_VERBOSE);
            }
            return false;
        }

        boolean done = setPropertyHook(ns, name, value, false, false, false);
        if (done) {
            return true;
        }

        if (null != properties.get(name) && verbose) {
            project.log("Overriding previous definition of property \"" + name
                + "\"", Project.MSG_VERBOSE);
        }

        if (verbose) {
            project.log("Setting project property: " + name + " -> "
                + value, Project.MSG_DEBUG);
        }
        properties.put(name, value);
        return true;
    }

    /**
     * Sets a property if no value currently exists. If the property
     * exists already, a message is logged and the method returns with
     * no other effect.
     *
     * @param ns   The namespace for the property (currently not used).
     * @param name The name of property to set.
     *             Must not be <code>null.
     * @param value The new value of the property.
     *              Must not be <code>null.
     * @since Ant 1.6
     */
    public synchronized void setNewProperty(String ns, String name,
                                            Object value) {
        if (null != properties.get(name)) {
            project.log("Override ignored for property \"" + name
                + "\"", Project.MSG_VERBOSE);
            return;
        }

        boolean done = setPropertyHook(ns, name, value, false, false, true);
        if (done) {
            return;
        }

        project.log("Setting project property: " + name + " -> "
            + value, Project.MSG_DEBUG);
        if (name != null && value != null) {
            properties.put(name, value);
        }
    }

    /**
     * Sets a user property, which cannot be overwritten by
     * set/unset property calls. Any previous value is overwritten.
     * @param ns   The namespace for the property (currently not used).
     * @param name The name of property to set.
     *             Must not be <code>null.
     * @param value The new value of the property.
     *              Must not be <code>null.
     */
    public synchronized void setUserProperty(String ns, String name,
                                             Object value) {
        project.log("Setting ro project property: " + name + " -> "
            + value, Project.MSG_DEBUG);
        userProperties.put(name, value);

        boolean done = setPropertyHook(ns, name, value, false, true, false);
        if (done) {
            return;
        }
        properties.put(name, value);
    }

    /**
     * Sets an inherited user property, which cannot be overwritten by set/unset
     * property calls. Any previous value is overwritten. Also marks
     * these properties as properties that have not come from the
     * command line.
     *
     * @param ns   The namespace for the property (currently not used).
     * @param name The name of property to set.
     *             Must not be <code>null.
     * @param value The new value of the property.
     *              Must not be <code>null.
     */
    public synchronized void setInheritedProperty(String ns, String name,
                                                  Object value) {
        inheritedProperties.put(name, value);

        project.log("Setting ro project property: " + name + " -> "
            + value, Project.MSG_DEBUG);
        userProperties.put(name, value);

        boolean done = setPropertyHook(ns, name, value, true, false, false);
        if (done) {
            return;
        }
        properties.put(name, value);
    }

    // -------------------- Getting properties  --------------------

    /**
     * Returns the value of a property, if it is set.  You can override
     * this method in order to plug your own storage.
     *
     * @param ns   The namespace for the property (currently not used).
     * @param name The name of the property.
     *             May be <code>null, in which case
     *             the return value is also <code>null.
     * @return the property value, or <code>null for no match
     *         or if a <code>null name is provided.
     */
    public synchronized Object getProperty(String ns, String name) {
        if (name == null) {
            return null;
        }

        Object o = getPropertyHook(ns, name, false);
        if (o != null) {
            return o;
        }

        return properties.get(name);
    }
    /**
     * Returns the value of a user property, if it is set.
     *
     * @param ns   The namespace for the property (currently not used).
     * @param name The name of the property.
     *             May be <code>null, in which case
     *             the return value is also <code>null.
     * @return the property value, or <code>null for no match
     *         or if a <code>null name is provided.
     */
    public synchronized Object getUserProperty(String ns, String name) {
        if (name == null) {
            return null;
        }
        Object o = getPropertyHook(ns, name, true);
        if (o != null) {
            return o;
        }
        return  userProperties.get(name);
    }


    // -------------------- Access to property tables  --------------------
    // This is used to support ant call and similar tasks. It should be
    // deprecated, it is possible to use a better (more efficient)
    // mechanism to preserve the context.

    /**
     * Returns a copy of the properties table.
     * @return a hashtable containing all properties
     *         (including user properties).
     */
    public Hashtable getProperties() {
        return new Hashtable(properties);
        // There is a better way to save the context. This shouldn't
        // delegate to next, it's for backward compatibility only.
    }

    /**
     * Returns a copy of the user property hashtable
     * @return a hashtable containing just the user properties
     */
    public Hashtable getUserProperties() {
        return new Hashtable(userProperties);
    }

    /**
     * special back door for subclasses, internal access to
     * the hashtables
     * @return the live hashtable of all properties
     */
    protected Hashtable getInternalProperties() {
        return properties;
    }

    /**
     * special back door for subclasses, internal access to
     * the hashtables
     *
     * @return the live hashtable of user properties
     */
    protected Hashtable getInternalUserProperties() {
        return userProperties;
    }

    /**
     * special back door for subclasses, internal access to
     * the hashtables
     *
     * @return the live hashtable inherited properties
     */
    protected Hashtable getInternalInheritedProperties() {
        return inheritedProperties;
    }


    /**
     * Copies all user properties that have not been set on the
     * command line or a GUI tool from this instance to the Project
     * instance given as the argument.
     *
     * <p>To copy all "user" properties, you will also have to call
     * {@link #copyUserProperties copyUserProperties}.</p>
     *
     * @param other the project to copy the properties to.  Must not be null.
     *
     * @since Ant 1.6
     */
    public void copyInheritedProperties(Project other) {
        Enumeration e = inheritedProperties.keys();
        while (e.hasMoreElements()) {
            String arg = e.nextElement().toString();
            if (other.getUserProperty(arg) != null) {
                continue;
            }
            Object value = inheritedProperties.get(arg);
            other.setInheritedProperty(arg, value.toString());
        }
    }

    /**
     * Copies all user properties that have been set on the command
     * line or a GUI tool from this instance to the Project instance
     * given as the argument.
     *
     * <p>To copy all "user" properties, you will also have to call
     * {@link #copyInheritedProperties copyInheritedProperties}.</p>
     *
     * @param other the project to copy the properties to.  Must not be null.
     *
     * @since Ant 1.6
     */
    public void copyUserProperties(Project other) {
        Enumeration e = userProperties.keys();
        while (e.hasMoreElements()) {
            Object arg = e.nextElement();
            if (inheritedProperties.containsKey(arg)) {
                continue;
            }
            Object value = userProperties.get(arg);
            other.setUserProperty(arg.toString(), value.toString());
        }
    }

    // -------------------- Property parsing  --------------------
    // Moved from ProjectHelper. You can override the static method -
    // this is used for backward compatibility (for code that calls
    // the parse method in ProjectHelper).

    /** Default parsing method. It is here only to support backward compatibility
     * for the static ProjectHelper.parsePropertyString().
     */
    static void parsePropertyStringDefault(String value, Vector fragments,
                                    Vector propertyRefs)
        throws BuildException {
        int prev = 0;
        int pos;
        //search for the next instance of $ from the 'prev' position
        while ((pos = value.indexOf("$", prev)) >= 0) {

            //if there was any text before this, add it as a fragment
            //TODO, this check could be modified to go if pos>prev;
            //seems like this current version could stick empty strings
            //into the list
            if (pos > 0) {
                fragments.addElement(value.substring(prev, pos));
            }
            //if we are at the end of the string, we tack on a $
            //then move past it
            if (pos == (value.length() - 1)) {
                fragments.addElement("$");
                prev = pos + 1;
            } else if (value.charAt(pos + 1) != '{') {
                //peek ahead to see if the next char is a property or not
                //not a property: insert the char as a literal
                /*
                fragments.addElement(value.substring(pos + 1, pos + 2));
                prev = pos + 2;
                */
                if (value.charAt(pos + 1) == '$') {
                    //backwards compatibility two $ map to one mode
                    fragments.addElement("$");
                    prev = pos + 2;
                } else {
                    //new behaviour: $X maps to $X for all values of X!='$'
                    fragments.addElement(value.substring(pos, pos + 2));
                    prev = pos + 2;
                }

            } else {
                //property found, extract its name or bail on a typo
                int endName = value.indexOf('}', pos);
                if (endName < 0) {
                    throw new BuildException("Syntax error in property: "
                                                 + value);
                }
                String propertyName = value.substring(pos + 2, endName);
                fragments.addElement(null);
                propertyRefs.addElement(propertyName);
                prev = endName + 1;
            }
        }
        //no more $ signs found
        //if there is any tail to the file, append it
        if (prev < value.length()) {
            fragments.addElement(value.substring(prev));
        }
    }

}