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Android example source code file (Binder.java)

This example Android source code file (Binder.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Android by Example" TM.

Java - Android tags/keywords

android, binder, binderproxy, fileoutputstream, find_potential_leaks, ibinder, iinterface, io, ioexception, parcel, printwriter, reflection, remoteexception, runtimeexception, string, throwable, util, utilities, utils, weakreference

The Binder.java Android example source code

/*
 * 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.os;

import android.util.Config;
import android.util.Log;

import java.io.FileDescriptor;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.PrintWriter;
import java.lang.ref.WeakReference;
import java.lang.reflect.Modifier;

/**
 * Base class for a remotable object, the core part of a lightweight
 * remote procedure call mechanism defined by {@link IBinder}.
 * This class is an implementation of IBinder that provides
 * the standard support creating a local implementation of such an object.
 * 
 * <p>Most developers will not implement this class directly, instead using the
 * <a href="{@docRoot}guide/developing/tools/aidl.html">aidl tool to describe the desired
 * interface, having it generate the appropriate Binder subclass.  You can,
 * however, derive directly from Binder to implement your own custom RPC
 * protocol or simply instantiate a raw Binder object directly to use as a
 * token that can be shared across processes.
 * 
 * @see IBinder
 */
public class Binder implements IBinder {
    /*
     * Set this flag to true to detect anonymous, local or member classes
     * that extend this Binder class and that are not static. These kind
     * of classes can potentially create leaks.
     */
    private static final boolean FIND_POTENTIAL_LEAKS = false;
    private static final String TAG = "Binder";

    private int mObject;
    private IInterface mOwner;
    private String mDescriptor;
    
    /**
     * Return the ID of the process that sent you the current transaction
     * that is being processed.  This pid can be used with higher-level
     * system services to determine its identity and check permissions.
     * If the current thread is not currently executing an incoming transaction,
     * then its own pid is returned.
     */
    public static final native int getCallingPid();
    
    /**
     * Return the ID of the user assigned to the process that sent you the
     * current transaction that is being processed.  This uid can be used with
     * higher-level system services to determine its identity and check
     * permissions.  If the current thread is not currently executing an
     * incoming transaction, then its own uid is returned.
     */
    public static final native int getCallingUid();
    
    /**
     * Reset the identity of the incoming IPC on the current thread.  This can
     * be useful if, while handling an incoming call, you will be calling
     * on interfaces of other objects that may be local to your process and
     * need to do permission checks on the calls coming into them (so they
     * will check the permission of your own local process, and not whatever
     * process originally called you).
     *
     * @return Returns an opaque token that can be used to restore the
     * original calling identity by passing it to
     * {@link #restoreCallingIdentity(long)}.
     *
     * @see #getCallingPid()
     * @see #getCallingUid()
     * @see #restoreCallingIdentity(long)
     */
    public static final native long clearCallingIdentity();

    /**
     * Restore the identity of the incoming IPC on the current thread
     * back to a previously identity that was returned by {@link
     * #clearCallingIdentity}.
     *
     * @param token The opaque token that was previously returned by
     * {@link #clearCallingIdentity}.
     *
     * @see #clearCallingIdentity
     */
    public static final native void restoreCallingIdentity(long token);
    
    /**
     * Flush any Binder commands pending in the current thread to the kernel
     * driver.  This can be
     * useful to call before performing an operation that may block for a long
     * time, to ensure that any pending object references have been released
     * in order to prevent the process from holding on to objects longer than
     * it needs to.
     */
    public static final native void flushPendingCommands();
    
    /**
     * Add the calling thread to the IPC thread pool.  This function does
     * not return until the current process is exiting.
     */
    public static final native void joinThreadPool();
    
    /**
     * Default constructor initializes the object.
     */
    public Binder() {
        init();

        if (FIND_POTENTIAL_LEAKS) {
            final Class<? extends Binder> klass = getClass();
            if ((klass.isAnonymousClass() || klass.isMemberClass() || klass.isLocalClass()) &&
                    (klass.getModifiers() & Modifier.STATIC) == 0) {
                Log.w(TAG, "The following Binder class should be static or leaks might occur: " +
                    klass.getCanonicalName());
            }
        }
    }
    
    /**
     * Convenience method for associating a specific interface with the Binder.
     * After calling, queryLocalInterface() will be implemented for you
     * to return the given owner IInterface when the corresponding
     * descriptor is requested.
     */
    public void attachInterface(IInterface owner, String descriptor) {
        mOwner = owner;
        mDescriptor = descriptor;
    }
    
    /**
     * Default implementation returns an empty interface name.
     */
    public String getInterfaceDescriptor() {
        return mDescriptor;
    }

    /**
     * Default implementation always returns true -- if you got here,
     * the object is alive.
     */
    public boolean pingBinder() {
        return true;
    }

    /**
     * {@inheritDoc}
     *
     * Note that if you're calling on a local binder, this always returns true
     * because your process is alive if you're calling it.
     */
    public boolean isBinderAlive() {
        return true;
    }
    
    /**
     * Use information supplied to attachInterface() to return the
     * associated IInterface if it matches the requested
     * descriptor.
     */
    public IInterface queryLocalInterface(String descriptor) {
        if (mDescriptor.equals(descriptor)) {
            return mOwner;
        }
        return null;
    }
    
    /**
     * Default implementation is a stub that returns false.  You will want
     * to override this to do the appropriate unmarshalling of transactions.
     *
     * <p>If you want to call this, call transact().
     */
    protected boolean onTransact(int code, Parcel data, Parcel reply,
            int flags) throws RemoteException {
        if (code == INTERFACE_TRANSACTION) {
            reply.writeString(getInterfaceDescriptor());
            return true;
        } else if (code == DUMP_TRANSACTION) {
            ParcelFileDescriptor fd = data.readFileDescriptor();
            String[] args = data.readStringArray();
            if (fd != null) {
                try {
                    dump(fd.getFileDescriptor(), args);
                } finally {
                    try {
                        fd.close();
                    } catch (IOException e) {
                    }
                }
            }
            return true;
        }
        return false;
    }

    /**
     * Implemented to call the more convenient version
     * {@link #dump(FileDescriptor, PrintWriter, String[])}.
     */
    public void dump(FileDescriptor fd, String[] args) {
        FileOutputStream fout = new FileOutputStream(fd);
        PrintWriter pw = new PrintWriter(fout);
        try {
            dump(fd, pw, args);
        } finally {
            pw.flush();
        }
    }
    
    /**
     * Print the object's state into the given stream.
     * 
     * @param fd The raw file descriptor that the dump is being sent to.
     * @param fout The file to which you should dump your state.  This will be
     * closed for you after you return.
     * @param args additional arguments to the dump request.
     */
    protected void dump(FileDescriptor fd, PrintWriter fout, String[] args) {
    }

    /**
     * Default implementation rewinds the parcels and calls onTransact.  On
     * the remote side, transact calls into the binder to do the IPC.
     */
    public final boolean transact(int code, Parcel data, Parcel reply,
            int flags) throws RemoteException {
        if (Config.LOGV) Log.v("Binder", "Transact: " + code + " to " + this);
        if (data != null) {
            data.setDataPosition(0);
        }
        boolean r = onTransact(code, data, reply, flags);
        if (reply != null) {
            reply.setDataPosition(0);
        }
        return r;
    }
    
    /**
     * Local implementation is a no-op.
     */
    public void linkToDeath(DeathRecipient recipient, int flags) {
    }

    /**
     * Local implementation is a no-op.
     */
    public boolean unlinkToDeath(DeathRecipient recipient, int flags) {
        return true;
    }
    
    protected void finalize() throws Throwable {
        try {
            destroy();
        } finally {
            super.finalize();
        }
    }
    
    private native final void init();
    private native final void destroy();
    private boolean execTransact(int code, int dataObj, int replyObj,
            int flags) {
        Parcel data = Parcel.obtain(dataObj);
        Parcel reply = Parcel.obtain(replyObj);
        // theoretically, we should call transact, which will call onTransact,
        // but all that does is rewind it, and we just got these from an IPC,
        // so we'll just call it directly.
        boolean res;
        try {
            res = onTransact(code, data, reply, flags);
        } catch (RemoteException e) {
            reply.writeException(e);
            res = true;
        } catch (RuntimeException e) {
            reply.writeException(e);
            res = true;
        }
        reply.recycle();
        data.recycle();
        return res;
    }
}

final class BinderProxy implements IBinder {
    public native boolean pingBinder();
    public native boolean isBinderAlive();
    
    public IInterface queryLocalInterface(String descriptor) {
        return null;
    }
    
    public native String getInterfaceDescriptor() throws RemoteException;
    public native boolean transact(int code, Parcel data, Parcel reply,
            int flags) throws RemoteException;
    public native void linkToDeath(DeathRecipient recipient, int flags)
            throws RemoteException;
    public native boolean unlinkToDeath(DeathRecipient recipient, int flags);

    public void dump(FileDescriptor fd, String[] args) throws RemoteException {
        Parcel data = Parcel.obtain();
        data.writeFileDescriptor(fd);
        data.writeStringArray(args);
        try {
            transact(DUMP_TRANSACTION, data, null, 0);
        } finally {
            data.recycle();
        }
    }
    
    BinderProxy() {
        mSelf = new WeakReference(this);
    }
    
    @Override
    protected void finalize() throws Throwable {
        try {
            destroy();
        } finally {
            super.finalize();
        }
    }
    
    private native final void destroy();
    
    private static final void sendDeathNotice(DeathRecipient recipient) {
        if (Config.LOGV) Log.v("JavaBinder", "sendDeathNotice to " + recipient);
        try {
            recipient.binderDied();
        }
        catch (RuntimeException exc) {
            Log.w("BinderNative", "Uncaught exception from death notification",
                    exc);
        }
    }
    
    final private WeakReference mSelf;
    private int mObject;
}

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