property.java

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    public void setClasspathRef(Reference r) {
        createClasspath().setRefid(r);
    }

    /**
     * Get the classpath used when looking up a resource.
     * @return the classpath
     * @since Ant 1.5
     */
    public Path getClasspath() {
        return classpath;
    }

    /**
     * @param userProperty ignored
     * @deprecated since 1.5.x.
     *             This was never a supported feature and has been
     *             deprecated without replacement.
     * @ant.attribute ignore="true"
     */
    public void setUserProperty(boolean userProperty) {
        log("DEPRECATED: Ignoring request to set user property in Property"
            + " task.", Project.MSG_WARN);
    }

    /**
     * get the value of this property
     * @return the current value or the empty string
     */
    public String toString() {
        return value == null ? "" : value;
    }

    /**
     * set the property in the project to the value.
     * if the task was give a file, resource or env attribute
     * here is where it is loaded
     * @throws BuildException on error
     */
    public void execute() throws BuildException {
        if (getProject() == null) {
            throw new IllegalStateException("project has not been set");
        }

        if (name != null) {
            if (value == null && ref == null) {
                throw new BuildException("You must specify value, location or "
                                         + "refid with the name attribute",
                                         getLocation());
            }
        } else {
            if (url == null && file == null && resource == null && env == null) {
                throw new BuildException("You must specify url, file, resource or "
                                         + "environment when not using the "
                                         + "name attribute", getLocation());
            }
        }

        if (url == null && file == null && resource == null && prefix != null) {
            throw new BuildException("Prefix is only valid when loading from "
                                     + "a url, file or resource", getLocation());
        }

        if ((name != null) && (value != null)) {
            addProperty(name, value);
        }

        if (file != null) {
            loadFile(file);
        }

        if (url != null) {
            loadUrl(url);
        }

        if (resource != null) {
            loadResource(resource);
        }

        if (env != null) {
            loadEnvironment(env);
        }

        if ((name != null) && (ref != null)) {
            try {
                addProperty(name,
                            ref.getReferencedObject(getProject()).toString());
            } catch (BuildException be) {
                if (fallback != null) {
                    addProperty(name,
                                ref.getReferencedObject(fallback).toString());
                } else {
                    throw be;
                }
            }
        }
    }

    /**
     * load properties from a url
     * @param url url to load from
     * @throws BuildException on error
     */
    protected void loadUrl(URL url) throws BuildException {
        Properties props = new Properties();
        log("Loading " + url, Project.MSG_VERBOSE);
        try {
            InputStream is = url.openStream();
            try {
                props.load(is);
            } finally {
                if (is != null) {
                    is.close();
                }
            }
            addProperties(props);
        } catch (IOException ex) {
            throw new BuildException(ex, getLocation());
        }
    }


    /**
     * load properties from a file
     * @param file file to load
     * @throws BuildException on error
     */
    protected void loadFile(File file) throws BuildException {
        Properties props = new Properties();
        log("Loading " + file.getAbsolutePath(), Project.MSG_VERBOSE);
        try {
            if (file.exists()) {
                FileInputStream  fis = null;
                try {
                    fis = new FileInputStream(file);
                    props.load(fis);
                } finally {
                    if (fis != null) {
                        fis.close();
                    }
                }
                addProperties(props);
            } else {
                log("Unable to find property file: " + file.getAbsolutePath(),
                    Project.MSG_VERBOSE);
            }
        } catch (IOException ex) {
            throw new BuildException(ex, getLocation());
        }
    }

    /**
     * load properties from a resource in the current classpath
     * @param name name of resource to load
     */
    protected void loadResource(String name) {
        Properties props = new Properties();
        log("Resource Loading " + name, Project.MSG_VERBOSE);
        InputStream is = null;
        try {
            ClassLoader cL = null;

            if (classpath != null) {
                cL = getProject().createClassLoader(classpath);
            } else {
                cL = this.getClass().getClassLoader();
            }

            if (cL == null) {
                is = ClassLoader.getSystemResourceAsStream(name);
            } else {
                is = cL.getResourceAsStream(name);
            }

            if (is != null) {
                props.load(is);
                addProperties(props);
            } else {
                log("Unable to find resource " + name, Project.MSG_WARN);
            }
        } catch (IOException ex) {
            throw new BuildException(ex, getLocation());
        } finally {
            if (is != null) {
                try {
                    is.close();
                } catch (IOException e) {
                    // ignore
                }
            }
        }

    }

    /**
     * load the environment values
     * @param prefix prefix to place before them
     */
    protected void loadEnvironment(String prefix) {
        Properties props = new Properties();
        if (!prefix.endsWith(".")) {
            prefix += ".";
        }
        log("Loading Environment " + prefix, Project.MSG_VERBOSE);
        Vector osEnv = Execute.getProcEnvironment();
        for (Enumeration e = osEnv.elements(); e.hasMoreElements();) {
            String entry = (String) e.nextElement();
            int pos = entry.indexOf('=');
            if (pos == -1) {
                log("Ignoring: " + entry, Project.MSG_WARN);
            } else {
                props.put(prefix + entry.substring(0, pos),
                entry.substring(pos + 1));
            }
        }
        addProperties(props);
    }

    /**
     * iterate through a set of properties,
     * resolve them then assign them
     * @param props the properties to iterate over
     */
    protected void addProperties(Properties props) {
        resolveAllProperties(props);
        Enumeration e = props.keys();
        while (e.hasMoreElements()) {
            String propertyName = (String) e.nextElement();
            String propertyValue = props.getProperty(propertyName);

            String v = getProject().replaceProperties(propertyValue);

            if (prefix != null) {
                propertyName = prefix + propertyName;
            }

            addProperty(propertyName, v);
        }
    }

    /**
     * add a name value pair to the project property set
     * @param n name of property
     * @param v value to set
     */
    protected void addProperty(String n, String v) {
        if (userProperty) {
            if (getProject().getUserProperty(n) == null) {
                getProject().setInheritedProperty(n, v);
            } else {
                log("Override ignored for " + n, Project.MSG_VERBOSE);
            }
        } else {
            getProject().setNewProperty(n, v);
        }
    }

    /**
     * resolve properties inside a properties hashtable
     * @param props properties object to resolve
     */
    private void resolveAllProperties(Properties props) throws BuildException {
        for (Enumeration e = props.keys(); e.hasMoreElements();) {
            String propertyName = (String) e.nextElement();
            Stack referencesSeen = new Stack();
            resolve(props, propertyName, referencesSeen);
        }
    }

    /**
     * Recursively expand the named property using the project's
     * reference table and the given set of properties - fail if a
     * circular definition is detected.
     *
     * @param props properties object to resolve
     * @param name of the property to resolve
     * @param referencesSeen stack of all property names that have
     * been tried to expand before coming here.
     */
    private void resolve(Properties props, String name, Stack referencesSeen)
        throws BuildException {
        if (referencesSeen.contains(name)) {
            throw new BuildException("Property " + name + " was circularly "
                                     + "defined.");
        }

        String propertyValue = props.getProperty(name);
        Vector fragments = new Vector();
        Vector propertyRefs = new Vector();
        PropertyHelper.getPropertyHelper(
            this.getProject()).parsePropertyString(
                propertyValue, fragments, propertyRefs);

        if (propertyRefs.size() != 0) {
            referencesSeen.push(name);
            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();
                    fragment = getProject().getProperty(propertyName);
                    if (fragment == null) {
                        if (props.containsKey(propertyName)) {
                            resolve(props, propertyName, referencesSeen);
                            fragment = props.getProperty(propertyName);
                        } else {
                            fragment = "${" + propertyName + "}";
                        }
                    }
                }
                sb.append(fragment);
            }
            propertyValue = sb.toString();
            props.put(name, propertyValue);
            referencesSeen.pop();
        }
    }
}