bug 44241 add JavaConstantResource to read string constants.

git-svn-id: https://svn.apache.org/repos/asf/ant/core/trunk@612079 13f79535-47bb-0310-9956-ffa450edef68

src/main/org/apache/tools/ant/types/resources/JavaConstantResource.java

@@ -0,0 +1,66 @@
+/*
+ * Copyright  2008 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.apache.tools.ant.types.resources;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.ByteArrayInputStream;
+import java.lang.reflect.Field;
+
+/**
+ * A resource that is a java constant.
+ * This lets you extract values off the classpath and use them elsewhere
+ * @since Ant1.7
+ *
+ */
+
+public class JavaConstantResource extends AbstractClasspathResource {
+    /**
+     * open the inpout stream from a specific classloader
+     *
+     * @param cl the classloader to use. Will be null if the system classloader is used
+     * @return an open input stream for the resource
+     * @throws IOException if an error occurs.
+     */
+    protected InputStream openInputStream(ClassLoader cl) throws IOException {
+        Class clazz;
+        String constant = getName();
+        int index1 = constant.lastIndexOf('.');
+        if (index1 < 0) {
+            throw new IOException("No class name in " + constant);
+        }
+        int index = index1;
+        String classname = constant.substring(0, index);
+        String fieldname = constant.substring(index + 1, constant.length());
+        try {
+            clazz = cl!=null?Class.forName(classname,true,cl):Class.forName(classname);
+            Field field = clazz.getField(fieldname);
+            String value=field.get(null).toString();
+            return new ByteArrayInputStream(value.getBytes("UTF-8"));
+        } catch (ClassNotFoundException e) {
+            throw new IOException("Class not found:"+ classname);
+        } catch (NoSuchFieldException e) {
+            throw new IOException("Field not found:" + fieldname+ " in "+classname);
+        } catch (IllegalAccessException e) {
+            throw new IOException("Illegal access to :" + fieldname + " in " + classname);
+        } catch (NullPointerException npe) {
+            throw new IOException("Not a static field: " + fieldname + " in " + classname);
+        }
+    }
+
+
+}