- localsocket是什么
- localsocket通信实例
在弄清localsocket是什么之前，有必要先了解下socket是什么。socket通常翻译为套接字，它是为了方便让两台机器能互相通信的一套技术，该套技术封装好了繁琐的tcp/ip协议，向外提供出简单的api简化了通信实现的过程，其可以实现不同层面，不同应用，跨进程跨网络的通信。依据socket提供的数据传输特性可分为如下几个大类：
- stream socket: 提供双向、有序、可靠、非重复的数据通信。大致可以认为它封装的tcp通信协议。
- datagram socket: 提供双向数据通信，数据不一定按顺序到达。大致可以认为它封装的是udp通信协议。
- sequential socket: 提供双向、有序、可靠数据通信，数据包有最大限制，并且必须把这个包完整的接受才能进行读取。
- raw socket: 提供相对tcp/udp而言较下层的通信协议访问，如果使用非tcp/udp的通信协议可以使用该类型的socket。
socket通信过程如下图
而android中的localsocket是基于unix-domain socket的，unix-domain socket是在socket的基础上衍生出来的一种ipc通信机制，因此localsocket解决的是同一台主机上不同进程间互相通信的问题。其相对于网络通信使用的socket不需要经过网络协议栈，不需要打包拆包、计算校验，自然的执行效率也高。与大名鼎鼎的binder机制作用一样，都在android系统中作为ipc通信手段被广泛使用。
在去代码看看
frameworks/base/core/java/android/net/localsocket.java
public class localsocket implements closeable {
private final localsocketimpl impl;
private volatile boolean implcreated;
private localsocketaddress localaddress;
private boolean isbound;
private boolean isconnected;
private final int socktype;
/** unknown socket type (used for constructor with existing file descriptor) */
/* package */ static final int socket_unknown = 0;
/** datagram socket type */
public static final int socket_dgram = 1;
/** stream socket type */
public static final int socket_stream = 2;
/** sequential packet socket type */
public static final int socket_seqpacket = 3;
// ...从上述代码片段引出了几个重要的相关类：
-
localsocketimpl: 如果看过jdk源码中的socket模块，其中有一个socketimpl类，客户端socket和服务端socket都是通过socketimpl创建出来的。对比来看localsocketimpl的作用跟socketimpl类似，不过这里还差一个服务端socket，查看localsocketimpl的类注释，
/** socket implementation used for android.net.localsocket and android.net.localserversocket. supports only af_local sockets. */ class localsocketimpl {类注释里清楚的阐述了localsocketimpl的作用，它是localsocket和localserversocket的实现类，并且只支持af_local类型的socket，而af_local就是unix域的本地socket类型。这里又出现了一个重要类localserversocket，它就是差的那个服务端socket.
-
localserversocket: 服务端的socket。
-
localsocketaddress: af_local类型socket的地址，做为localsocket和 localserversocket互相通信的标示。这个标示可以放在三个不同的namespace下。具体如下
abstract linux 抽象命名空间 reserved android系统预定的命名空间，其路径在/dev/socket下 filesystem 传统的文件系统命名空间 android系统可以通过命令
adb shell netstat -apn
查看socket所处的命名空间，下图是本地截取的部分输出。
一般两个不同的应用之间如果要相互通信，首先想到的ag真人游戏的解决方案都是利用aidl，这里我们用localsocket来实现。通过该例子来实践下localsocket。
先看看运行效果图。
testlocalsocketserver和testlocalsocketclient是不同的两个应用，我们从testlocalsocketclient输入一个字串，然后在testlocalsocketserver显示出来。
testlocalsocketserver核心代码：
public class serveractivity extends activity {
private localserversocket mserversocket = null;
private localsocket msocket = null;
private textview mshowmsg = null;
private inputstream minputstream = null;
private static final string socket_name = "com.azhengye.testsocket";
private static final string tag = "azhengye-socket";
private final handler mhandler = new handler() {
public void handlemessage(android.os.message msg) {
string dispmesg = (string) msg.obj;
mshowmsg.settext(dispmesg);
};
};
@override
protected void oncreate(bundle savedinstancestate) {
super.oncreate(savedinstancestate);
setcontentview(r.layout.activity_main);
button button = (button) findviewbyid(r.id.replay_btn);
mshowmsg = (textview) findviewbyid(r.id.display_msg);
createserversocket();// 创建localserversocket
new thread(new runnable() {
@override
public void run() {
acceptmsg();//必须要在子线程里接收消息
}
}).start();
}
private void createserversocket() {
if (mserversocket == null) {
try {
/**注意这里new出localserversocket的同时，系统层已经同步做了bind和listen。
* 我们看看new的过程：
* public localserversocket(string name) throws ioexception {
* impl = new localsocketimpl();
* impl.create(localsocket.socket_stream);
* localaddress = new localsocketaddress(name);
* impl.bind(localaddress);
* impl.listen(listen_backlog);
* }
*/
mserversocket = new localserversocket(socket_name);
} catch (ioexception ex) {
throw new runtimeexception(
"error binding to local socket " ex);
}
}
}
private void acceptmsg() {
try {
msocket = mserversocket.accept();//accept是个阻塞方法，这就是必须要在子线程接收消息的原因。
} catch (ioexception e1) {
e1.printstacktrace();
}
while (true) {
try {
byte[] buffer = new byte[1024];
minputstream = msocket.getinputstream();
int count = minputstream.read(buffer);
string key = new string(arrays.copyofrange(buffer, 0, count));
log.d(tag, "serveractivity msocketoutstream==" key);
if ("stop".equals(key)) {
closesocketresource();
break;
}
message msg = mhandler.obtainmessage();
msg.obj = key;
msg.sendtotarget();
} catch (ioexception e) {
log.d(tag, "exception==" e.fillinstacktrace().getmessage());
e.printstacktrace();
}
}
}
private void closesocketresource() {
closeslient(minputstream);
closeslient(msocket);
try {
if (mserversocket != null) {
mserversocket.close();
mserversocket = null;
}
} catch (ioexception ex) {
log.e(tag, "failed closing serversocket" ex.fillinstacktrace());
}
}
private void closeslient(closeable closeable){
try {
if (closeable != null) {
closeable.close();
closeable = null;
}
} catch (ioexception ex) {
log.e(tag, "failed closing : " closeable);
}
}
}启动testlocalsocketserver使用命令：
adb shell netstat -apn|grep testsocket
输出
unix 2 [ acc ] stream listening 898034 12421/[email protected]则表明testlocalsocketserver已经就绪，等待客户端socket接入发送消息了。
testlocalsocketclient核心代码：
public class clientactivity extends activity implements onclicklistener{
private localsocket msocket;
private outputstream mout;
private edittext medittext = null;
private static final string socket_name = "com.azhengye.testsocket";//这里必须要跟testlocalsocketserver中定义的一样
private static final string tag = "azhengye-socket";
@override
protected void oncreate(bundle savedinstancestate) {
super.oncreate(savedinstancestate);
setcontentview(r.layout.activity_main);
connect();
medittext = (edittext) findviewbyid(r.id.input_msg);
findviewbyid(r.id.replay_btn).setonclicklistener(this);
findviewbyid(r.id.stop_btn).setonclicklistener(this);
}
private boolean connect() {
if (msocket != null) {
return true;
}
try {
msocket = new localsocket();//创建localsocket，模拟客户端
localsocketaddress address = new localsocketaddress(socket_name,
localsocketaddress.namespace.abstract);
msocket.connect(address);//连接testlocalsocketserver
} catch (ioexception ex) {
return false;
}
return true;
}
private boolean writecommand(string cmdstring) {
final byte[] cmd = cmdstring.getbytes();
final int len = cmd.length;
try {
mout = msocket.getoutputstream();
mout.write(cmd, 0, len);
log.i(tag, "clientactivity write " new string(cmd));
} catch (ioexception ex) {
log.e(tag, "clientactivity write error:" ex.fillinstacktrace());
return false;
}
return true;
}
@override
public void onclick(view v) {
switch (v.getid()) {
case r.id.replay_btn:
writecommand(medittext.gettext().tostring());
break;
case r.id.stop_btn:
writecommand("stop");
break;
default:
break;
}
}
}启动testlocalsocketclient使用命令：
adb shell netstat -apn|grep testsocket
输出
unix 3 [ ] stream connected 902376 12421/[email protected]则表明testlocalsocketclient已经连接上了testlocalsocketserver，可以给testlocalsocketserver发送消息了。