Fix the exception thrown by getDeclaredFields if the class is unavailable.

http://b/issue?id=2634005

Change-Id: I1ebad41a29c9527565efea539b8f2b31f117f370

1 files changed, 131 insertions, 0 deletions

diff --git a/support/src/test/java/tests/util/ClassLoaderBuilder.java b/support/src/test/java/tests/util/ClassLoaderBuilder.java
new file mode 100644
index 0000000..8fd18c2
--- /dev/null
+++ b/support/src/test/java/tests/util/ClassLoaderBuilder.java
@@ -0,0 +1,131 @@
+/*
+ * Copyright (C) 2010 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 tests.util;
+
+import java.io.File;
+import java.net.MalformedURLException;
+import java.net.URL;
+import java.net.URLClassLoader;
+import java.util.ArrayList;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Set;
+
+/**
+ * Builds a configured class loader. The constructed class loader can load a
+ * private copy of a class in addition to the copy in the application class
+ * loader. It can also refuse to load a class altogether, even if that class
+ * exists on the classpath.
+ */
+public final class ClassLoaderBuilder {
+    private ClassLoader parent = ClassLoaderBuilder.class.getClassLoader();
+    private final Set<String> prefixesToNotInherit = new HashSet<String>();
+    private final Set<String> prefixesToLoad = new HashSet<String>();
+
+    public ClassLoaderBuilder parent(ClassLoader parent) {
+        this.parent = parent;
+        return this;
+    }
+
+    /**
+     * @param classNamePrefix the prefix of classes that can be loaded by both
+     *     the constructed class loader and the application class loader.
+     */
+    public ClassLoaderBuilder withPrivateCopy(String classNamePrefix) {
+        prefixesToLoad.add(classNamePrefix);
+        return this;
+    }
+
+    /**
+     * @param classNamePrefix the prefix of classes that will not be loaded by
+     *     this class loader. Attempts to load such classes will fail at runtime
+     *     with a NoClassDefFoundError.
+     */
+    public ClassLoaderBuilder without(String classNamePrefix) {
+        prefixesToNotInherit.add(classNamePrefix);
+        return this;
+    }
+
+    public ClassLoader build() {
+        // make a defensive copy in case this builder is reused!
+        final Set<String> prefixesToNotInherit = new HashSet<String>(this.prefixesToNotInherit);
+        final Set<String> prefixesToLoad = new HashSet<String>(this.prefixesToLoad);
+
+        /*
+         * To load two copies of a given class in the VM, we end up creating two
+         * new class loaders: a bridge class loader and a leaf class loader.
+         *
+         * The bridge class loader is a child of the application class loader.
+         * It never loads any classes. All it does is decide when to delegate to
+         * the application class loader (which has a copy of everything) and
+         * when to fail.
+         *
+         * The leaf class loader is a child of the bridge class loader. It
+         * uses the same classpath as the application class loader. It loads
+         * anything that its parent failed on.
+         */
+
+        ClassLoader bridge = new ClassLoader(parent) {
+            @Override protected Class<?> loadClass(String className, boolean resolve)
+                    throws ClassNotFoundException {
+                for (String prefix : prefixesToLoad) {
+                    if (className.startsWith(prefix)) {
+                        /* ClassNotFoundException causes the child loader to load the class. */
+                        throw new ClassNotFoundException();
+                    }
+                }
+
+                for (String prefix : prefixesToNotInherit) {
+                    if (className.startsWith(prefix)) {
+                        /* NoClassDefFoundError prevents the class from being loaded at all. */
+                        throw new NoClassDefFoundError();
+                    }
+                }
+
+                return super.loadClass(className, resolve);
+            }
+        };
+
+        try {
+            // first try to create a PathClassLoader for a dalvik VM...
+            String classPath = System.getProperty("java.class.path");
+            return (ClassLoader) Class.forName("dalvik.system.PathClassLoader")
+                    .getConstructor(String.class, ClassLoader.class)
+                    .newInstance(classPath, bridge);
+        } catch (Exception ignored) {
+        }
+
+        // fall back to a URLClassLoader on a JVM
+        List<URL> classpath = new ArrayList<URL>();
+        classpath.addAll(classpathToUrls("java.class.path"));
+        classpath.addAll(classpathToUrls("sun.boot.class.path"));
+        return new URLClassLoader(classpath.toArray(new URL[classpath.size()]), bridge);
+    }
+
+    private List<URL> classpathToUrls(String propertyName) {
+        try {
+            String classpath = System.getProperty(propertyName);
+            List<URL> result = new ArrayList<URL>();
+            for (String pathElement : classpath.split(File.pathSeparator)) {
+                result.add(new File(pathElement).toURI().toURL());
+            }
+            return result;
+        } catch (MalformedURLException e) {
+            throw new RuntimeException(e);
+        }
+    }
+}