Add an XPath Ant task to be used in the android_rules.xml file.

This task is designed to run XPath expression targetting Android XML files.
It will handle the Android namespace with the 'android' prefix, and store
the result of the XPath into a property.

Change-Id: I9094f5661d5e1ef86553ee1c54bdeca62366e0cd
classname: XPathTask
classpath: anttasks.jar, sdklib.jar

Usage:
<xpathtask input="path/of/file/to/read" output="name.of.property.to.write"
    expression="/xpath/expression/to/evaluate" />

tools/anttasks/src/com/android/ant/XPathTask.java

@@ -0,0 +1,80 @@
+/*
+ * Copyright (C) 2009 The Android Open Source Project
+ *
+ * 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 com.android.ant;
+
+import org.apache.tools.ant.BuildException;
+import org.apache.tools.ant.Task;
+import org.apache.tools.ant.types.Path;
+import org.xml.sax.InputSource;
+
+import java.io.FileInputStream;
+import java.io.FileNotFoundException;
+
+import javax.xml.xpath.XPath;
+import javax.xml.xpath.XPathExpressionException;
+
+/**
+ * Android specific XPath task.
+ * The goal is to get the result of an XPath expression on Android XML files. The android namespace
+ * (http://schemas.android.com/apk/res/android) must be associated to the "android" prefix.
+ */
+public class XPathTask extends Task {
+
+    private Path mManifestFile;
+    private String mProperty;
+    private String mExpression;
+
+    public void setInput(Path manifestFile) {
+        mManifestFile = manifestFile;
+    }
+
+    public void setOutput(String property) {
+        mProperty = property;
+    }
+
+    public void setExpression(String expression) {
+        mExpression = expression;
+    }
+
+    @Override
+    public void execute() throws BuildException {
+        try {
+            if (mManifestFile == null || mManifestFile.list().length == 0) {
+                throw new BuildException("input attribute is missing!");
+            }
+
+            if (mProperty == null) {
+                throw new BuildException("output attribute is missing!");
+            }
+
+            if (mExpression == null) {
+                throw new BuildException("expression attribute is missing!");
+            }
+
+            XPath xpath = AndroidXPathFactory.newXPath();
+
+            String file = mManifestFile.list()[0];
+            String result = xpath.evaluate(mExpression, new InputSource(new FileInputStream(file)));
+
+            getProject().setProperty(mProperty, result);
+        } catch (XPathExpressionException e) {
+            throw new BuildException(e);
+        } catch (FileNotFoundException e) {
+            throw new BuildException(e);
+        }
+    }
+}