安卓高手之路之ClassLoader(四)

显然，应用层的classLoader绝对不仅仅是一个systemclassloader那么简单。那么他一定是与PackageInfo连接起来的。而这个连接的纽带就是ContextImpl。ContextImpl又与apk一一对应。

    @Override
    public ClassLoader getClassLoader() {
        return mPackageInfo != null ?
                mPackageInfo.getClassLoader() : ClassLoader.getSystemClassLoader();
    }

    public ClassLoader getClassLoader() {
        synchronized (this) {
            if (mClassLoader != null) {
                return mClassLoader;
            }

            if (mIncludeCode && !mPackageName.equals("android")) {
                String zip = mAppDir;

                /*
                 * The following is a bit of a hack to inject
                 * instrumentation into the system: If the app
                 * being started matches one of the instrumentation names,
                 * then we combine both the "instrumentation" and
                 * "instrumented" app into the path, along with the
                 * concatenation of both apps' shared library lists.
                 */

                String instrumentationAppDir =
                        mActivityThread.mInstrumentationAppDir;
                String instrumentationAppPackage =
                        mActivityThread.mInstrumentationAppPackage;
                String instrumentedAppDir =
                        mActivityThread.mInstrumentedAppDir;
                String[] instrumentationLibs = null;

                if (mAppDir.equals(instrumentationAppDir)
                        || mAppDir.equals(instrumentedAppDir)) {
                    zip = instrumentationAppDir + ":" + instrumentedAppDir;
                    if (! instrumentedAppDir.equals(instrumentationAppDir)) {
                        instrumentationLibs =
                            getLibrariesFor(instrumentationAppPackage);
                    }
                }

                if ((mSharedLibraries != null) ||
                        (instrumentationLibs != null)) {
                    zip =
                        combineLibs(mSharedLibraries, instrumentationLibs)
                        + ':' + zip;
                }

                /*
                 * With all the combination done (if necessary, actually
                 * create the class loader.
                 */

                if (ActivityThread.localLOGV)
                    Slog.v(ActivityThread.TAG, "Class path: " + zip + ", JNI path: " + mLibDir);

                // Temporarily disable logging of disk reads on the Looper thread
                // as this is early and necessary.
                StrictMode.ThreadPolicy oldPolicy = StrictMode.allowThreadDiskReads();

                mClassLoader =
                    ApplicationLoaders.getDefault().getClassLoader(
                        zip, mLibDir, mBaseClassLoader);
                initializeJavaContextClassLoader();

                StrictMode.setThreadPolicy(oldPolicy);
            } else {
                if (mBaseClassLoader == null) {
                    mClassLoader = ClassLoader.getSystemClassLoader();
                } else {
                    mClassLoader = mBaseClassLoader;
                }
            }
            return mClassLoader;
        }
    }

 mClassLoader =
                    ApplicationLoaders.getDefault().getClassLoader(
                        zip, mLibDir, mBaseClassLoader);

 /*
 * Copyright (C) 2006 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 android.app;

import dalvik.system.PathClassLoader;

import java.util.HashMap;
import java.util.Map;

class ApplicationLoaders
{
    public static ApplicationLoaders getDefault()
    {
        return gApplicationLoaders;
    }

    public ClassLoader getClassLoader(String zip, String libPath, ClassLoader parent)
    {
        /*
         * This is the parent we use if they pass "null" in.  In theory
         * this should be the "system" class loader; in practice we
         * don't use that and can happily (and more efficiently) use the
         * bootstrap class loader.
         */
        ClassLoader baseParent = ClassLoader.getSystemClassLoader().getParent();

        synchronized (mLoaders) {
            if (parent == null) {
                parent = baseParent;
            }

            /*
             * If we're one step up from the base class loader, find
             * something in our cache.  Otherwise, we create a whole
             * new ClassLoader for the zip archive.
             */
            if (parent == baseParent) {
                ClassLoader loader = mLoaders.get(zip);
                if (loader != null) {
                    return loader;
                }
    
                PathClassLoader pathClassloader =
                    new PathClassLoader(zip, libPath, parent);
                
                mLoaders.put(zip, pathClassloader);
                return pathClassloader;
            }

            return new PathClassLoader(zip, parent);
        }
    }

    private final Map<String, ClassLoader> mLoaders = new HashMap<String, ClassLoader>();

    private static final ApplicationLoaders gApplicationLoaders
        = new ApplicationLoaders();
}

 所有的东西都在这里。具体不多说了。看了就明白。

还有一个活动当前调用的classLoader。如下：

static void Dalvik_dalvik_system_VMStack_getCallingClassLoader(const u4* args,
    JValue* pResult)
{
    ClassObject* clazz =
        dvmGetCaller2Class(dvmThreadSelf()->interpSave.curFrame);

    UNUSED_PARAMETER(args);

    if (clazz == NULL)
        RETURN_PTR(NULL);
    RETURN_PTR(clazz->classLoader);
}

 java层为VMStack.java

  native public static ClassLoader getCallingClassLoader();

 可以直接认为是加载当前类的classLoader。如果是BootClassLoader，那么就返回null