该类继承自SocketImpl类
该类引入了如下包:
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.FileDescriptor;
import sun.net.ConnectionResetException;
import sun.net.NetHooks;
import sun.net.ResourceManager;
该类的类头注释如下:
/**
* Default Socket Implementation. This implementation does
* not implement any security checks.
* Note this class should <b>NOT</b> be public.
*
* @author Steven B. Byrne
*/
大意如下:
默认的套接字实现方式
该实现方式不执行一些安全检查
该类非public类
该类含有如下的成员变量:
超时时间
int timeout;
IP服务类型
private int trafficClass;
中止读取信号
private boolean shut_rd = false;
中止写入信号
private boolean shut_wr = false;
套接字输入流
private SocketInputStream socketInputStream = null;
套接字输出流
private SocketOutputStream socketOutputStream = null;
使用文件描述符的线程数
protected int fdUseCount = 0;
文件描述符控制锁
protected final Object fdLock = new Object();
文件描述符的关闭状态
protected boolean closePending = false;
连接状态指示
private int CONNECTION_NOT_RESET = 0;
private int CONNECTION_RESET_PENDING = 1;
private int CONNECTION_RESET = 2;
针对上述种类的状态记录
private int resetState;
重置锁
private final Object resetLock = new Object();
判定是TCP还是UDP(true是TCP,false是UDP;不过不是很清楚为啥要叫字段stream……)
protected boolean stream;
常量声明
public final static int SHUT_RD = 0;
public final static int SHUT_WR = 1;
该类含有如下的成员方法:
构造函数(同步的构造函数,需要运输层传送方法)
protected synchronized void create(boolean stream) throws IOException {
this.stream = stream;
if (!stream) {//为UDP
ResourceManager.beforeUdpCreate();
// only create the fd after we know we will be able to create the socket
fd = new FileDescriptor();
try {
socketCreate(false);//创建UDP的Socket
} catch (IOException ioe) {
ResourceManager.afterUdpClose();
fd = null;
throw ioe;
}
} else {//创建TCP
fd = new FileDescriptor();
socketCreate(true);
}
if (socket != null)
socket.setCreated();//父类包含的Socket变量
if (serverSocket != null)
serverSocket.setCreated();//父类包含的ServerSocket
}
创建连接(目标主机名和目的端口
protected void connect(String host, int port)
throws UnknownHostException, IOException
{
boolean connected = false;
try {
InetAddress address = InetAddress.getByName(host);//DNS获得主机地址
this.port = port;
this.address = address;
connectToAddress(address, port, timeout);//创建连接
connected = true;
} finally {
if (!connected) {//连接失败
try {
close();//关闭Socket
} catch (IOException ioe) {
/* Do nothing. If connect threw an exception then
it will be passed up the call stack */
}
}
}
}
创建连接(主机地址和端口
protected void connect(InetAddress address, int port) throws IOException {
this.port = port;
this.address = address;
try {
connectToAddress(address, port, timeout);
return;
} catch (IOException e) {
// everything failed
close();
throw e;
}
}
创建连接(一个完成SockAddress接口的(主机地址),和连接时限)
protected void connect(SocketAddress address, int timeout)
throws IOException {
boolean connected = false;
try {
if (address == null || !(address instanceof InetSocketAddress))//不是实际地址就炸
throw new IllegalArgumentException("unsupported address type");
InetSocketAddress addr = (InetSocketAddress) address;
if (addr.isUnresolved())
throw new UnknownHostException(addr.getHostName());
this.port = addr.getPort();
this.address = addr.getAddress();
connectToAddress(this.address, port, timeout);
connected = true;
} finally {
if (!connected) {
try {
close();
} catch (IOException ioe) {
/* Do nothing. If connect threw an exception then
it will be passed up the call stack */
}
}
}
}
创建连接(上面一个的进化版,多了时限
private void connectToAddress(InetAddress address, int port, int timeout) throws IOException {
if (address.isAnyLocalAddress()) {//判定是不是本地地址
doConnect(InetAddress.getLocalHost(), port, timeout);
} else {
doConnect(address, port, timeout);
}
}
网络连接权限(根据具体的操作号,后面对应的实体种类不同),该方法只是整合参数,具体设置在SocketSetOption里
public void setOption(int opt, Object val) throws SocketException {
if (isClosedOrPending()) {//判定当前套接字状态
throw new SocketException("Socket Closed");
}
boolean on = true;
switch (opt) {//根据操作权限码选择
/* check type safety b4 going native. These should never
* fail, since only java.Socket* has access to
* PlainSocketImpl.setOption().
*/
case SO_LINGER:
if (val == null || (!(val instanceof Integer) && !(val instanceof Boolean)))
throw new SocketException("Bad parameter for option");
if (val instanceof Boolean) {
/* true only if disabling - enabling should be Integer */
on = false;
}
break;
case SO_TIMEOUT://设置超时时限
if (val == null || (!(val instanceof Integer)))
throw new SocketException("Bad parameter for SO_TIMEOUT");
int tmp = ((Integer) val).intValue();
if (tmp < 0)
throw new IllegalArgumentException("timeout < 0");
timeout = tmp;
break;
case IP_TOS://设置IP头控制字段(type of service
if (val == null || !(val instanceof Integer)) {
throw new SocketException("bad argument for IP_TOS");
}
trafficClass = ((Integer)val).intValue();//设置控制字段
break;
case SO_BINDADDR://绑定地址
throw new SocketException("Cannot re-bind socket");
case TCP_NODELAY://TCP 无延迟发包
if (val == null || !(val instanceof Boolean))
throw new SocketException("bad parameter for TCP_NODELAY");
on = ((Boolean)val).booleanValue();
break;
case SO_SNDBUF:
case SO_RCVBUF://设置发送和接收缓冲大小
if (val == null || !(val instanceof Integer) ||
!(((Integer)val).intValue() > 0)) {
throw new SocketException("bad parameter for SO_SNDBUF " +
"or SO_RCVBUF");
}
break;
case SO_KEEPALIVE://链接保持
if (val == null || !(val instanceof Boolean))
throw new SocketException("bad parameter for SO_KEEPALIVE");
on = ((Boolean)val).booleanValue();
break;
case SO_OOBINLINE:
if (val == null || !(val instanceof Boolean))
throw new SocketException("bad parameter for SO_OOBINLINE");
on = ((Boolean)val).booleanValue();
break;
case SO_REUSEADDR://重定位地址
if (val == null || !(val instanceof Boolean))
throw new SocketException("bad parameter for SO_REUSEADDR");
on = ((Boolean)val).booleanValue();
break;
default:
throw new SocketException("unrecognized TCP option: " + opt);
}
socketSetOption(opt, on, val);
}
获得具体操作设置字段的值(逻辑基本和上一个方法一样
public Object getOption(int opt) throws SocketException {
if (isClosedOrPending()) {
throw new SocketException("Socket Closed");
}
if (opt == SO_TIMEOUT) {
return new Integer(timeout);
}
int ret = 0;
/*
* The native socketGetOption() knows about 3 options.
* The 32 bit value it returns will be interpreted according
* to what we're asking. A return of -1 means it understands
* the option but its turned off. It will raise a SocketException
* if "opt" isn't one it understands.
*/
switch (opt) {
case TCP_NODELAY:
ret = socketGetOption(opt, null);
return Boolean.valueOf(ret != -1);
case SO_OOBINLINE:
ret = socketGetOption(opt, null);
return Boolean.valueOf(ret != -1);
case SO_LINGER:
ret = socketGetOption(opt, null);
return (ret == -1) ? Boolean.FALSE: (Object)(new Integer(ret));
case SO_REUSEADDR:
ret = socketGetOption(opt, null);
return Boolean.valueOf(ret != -1);
case SO_BINDADDR:
InetAddressContainer in = new InetAddressContainer();
ret = socketGetOption(opt, in);
return in.addr;
case SO_SNDBUF:
case SO_RCVBUF:
ret = socketGetOption(opt, null);
return new Integer(ret);
case IP_TOS:
try {
ret = socketGetOption(opt, null);
if (ret == -1) { // ipv6 tos
return trafficClass;
} else {
return ret;
}
} catch (SocketException se) {
// TODO - should make better effort to read TOS or TCLASS
return trafficClass; // ipv6 tos
}
case SO_KEEPALIVE:
ret = socketGetOption(opt, null);
return Boolean.valueOf(ret != -1);
// should never get here
default:
return null;
}
}
同步进行TCP链接
synchronized void doConnect(InetAddress address, int port, int timeout) throws IOException {
synchronized (fdLock) {
if (!closePending && (socket == null || !socket.isBound())) {
NetHooks.beforeTcpConnect(fd, address, port);//建立TCP
}
}
try {
acquireFD();//获得当前套接字的描述符
try {
socketConnect(address, port, timeout);
/* socket may have been closed during poll/select */
synchronized (fdLock) {
if (closePending) {
throw new SocketException ("Socket closed");
}
}
// If we have a ref. to the Socket, then sets the flags
// created, bound & connected to true.
// This is normally done in Socket.connect() but some
// subclasses of Socket may call impl.connect() directly!
if (socket != null) {
socket.setBound();
socket.setConnected();
}
} finally {
releaseFD();//归还文件描述符的使用权
}
} catch (IOException e) {
close();
throw e;
}
}
对某个端口监听(参数是时间)
protected synchronized void listen(int count) throws IOException {
socketListen(count);
}
接收某个连接请求(来自Scoket实例
protected void accept(SocketImpl s) throws IOException {
acquireFD();
try {
socketAccept(s);
} finally {
releaseFD();
}
}
获得Socket的数据输入流
protected synchronized InputStream getInputStream() throws IOException {
synchronized (fdLock) {
if (isClosedOrPending())
throw new IOException("Socket Closed");
if (shut_rd)
throw new IOException("Socket input is shutdown");
if (socketInputStream == null)
socketInputStream = new SocketInputStream(this);
}
return socketInputStream;
}
设置数据输入流为特定输入流
void setInputStream(SocketInputStream in) {
socketInputStream = in;
}
获得套接字输出流(就是发送给链接方的数据
protected synchronized OutputStream getOutputStream() throws IOException {
synchronized (fdLock) {
if (isClosedOrPending())
throw new IOException("Socket Closed");
if (shut_wr)
throw new IOException("Socket output is shutdown");
if (socketOutputStream == null)
socketOutputStream = new SocketOutputStream(this);
}
return socketOutputStream;
}
设置当前的所操作的Socket(实质Socket和文件描述符绑定
void setFileDescriptor(FileDescriptor fd) {
this.fd = fd;
}
设置目的主机地址
void setAddress(InetAddress address) {
this.address = address;
}
设置目的端口
void setPort(int port) {
this.port = port;
}
设置本地监听端口
void setLocalPort(int localport) {
this.localport = localport;
}
返回当前Socket链接的有效性
protected synchronized int available() throws IOException {
if (isClosedOrPending()) {
throw new IOException("Stream closed.");
}
/*
* If connection has been reset or shut down for input, then return 0
* to indicate there are no buffered bytes.
*/
if (isConnectionReset() || shut_rd) {
return 0;
}
/*
* If no bytes available and we were previously notified
* of a connection reset then we move to the reset state.
*
* If are notified of a connection reset then check
* again if there are bytes buffered on the socket.
*/
int n = 0;
try {
n = socketAvailable();//当前无效
if (n == 0 && isConnectionResetPending()) {//重新设置链接
setConnectionReset();
}
} catch (ConnectionResetException exc1) {
setConnectionResetPending();//设置成预备重设状态
try {
n = socketAvailable();//再次尝试获得有效性
if (n == 0) {//如果仍然无效就再次重设
setConnectionReset();
}
} catch (ConnectionResetException exc2) {
}
}
return n;
}
关闭链接
protected void close() throws IOException {
synchronized(fdLock) {
if (fd != null) {
if (!stream) {
ResourceManager.afterUdpClose();
}
if (fdUseCount == 0) {
if (closePending) {
return;
}
closePending = true;
/*
* We close the FileDescriptor in two-steps - first the
* "pre-close" which closes the socket but doesn't
* release the underlying file descriptor. This operation
* may be lengthy due to untransmitted data and a long
* linger interval. Once the pre-close is done we do the
* actual socket to release the fd.
*/
try {
socketPreClose();
} finally {
socketClose();
}
fd = null;
return;
} else {
/*
* If a thread has acquired the fd and a close
* isn't pending then use a deferred close.
* Also decrement fdUseCount to signal the last
* thread that releases the fd to close it.
*/
if (!closePending) {
closePending = true;
fdUseCount--;
socketPreClose();
}
}
}
}
}
重新设置链接
void reset() throws IOException {
if (fd != null) {
socketClose();
}
fd = null;
super.reset();
}
中止从套接字中输入数据
protected void shutdownInput() throws IOException {
if (fd != null) {
socketShutdown(SHUT_RD);
if (socketInputStream != null) {
socketInputStream.setEOF(true);
}
shut_rd = true;
}
}
中止向套接字中输出数据
protected void shutdownOutput() throws IOException {
if (fd != null) {
socketShutdown(SHUT_WR);
shut_wr = true;
}
}
支持立即提交功能
protected boolean supportsUrgentData () {
return true;
}
发送紧急数据
protected void sendUrgentData (int data) throws IOException {
if (fd == null) {
throw new IOException("Socket Closed");
}
socketSendUrgentData (data);
}
最终操作(一般是用户用完忘了关
protected void finalize() throws IOException {
close();
}
请求文件描述符(对该套接字使用请求
FileDescriptor acquireFD() {
synchronized (fdLock) {
fdUseCount++;
return fd;
}
}
释放文件描述符(对该套接字释放
void releaseFD() {
synchronized (fdLock) {
fdUseCount--;
if (fdUseCount == -1) {
if (fd != null) {
try {
socketClose();
} catch (IOException e) {
} finally {
fd = null;
}
}
}
}
}
返回状态位(是否重置链接
public boolean isConnectionReset() {
synchronized (resetLock) {
return (resetState == CONNECTION_RESET);
}
}
返回状态位(是否期待重设链接
public boolean isConnectionResetPending() {
synchronized (resetLock) {
return (resetState == CONNECTION_RESET_PENDING);
}
}
设置状态位(链接重置
public void setConnectionReset() {
synchronized (resetLock) {
resetState = CONNECTION_RESET;
}
}
设置状态位(链接需要重置
public void setConnectionResetPending() {
synchronized (resetLock) {
if (resetState == CONNECTION_NOT_RESET) {
resetState = CONNECTION_RESET_PENDING;
}
}
}
是否已经关闭或者期待关闭
public boolean isClosedOrPending() {
/*
* Lock on fdLock to ensure that we wait if a
* close is in progress.
*/
synchronized (fdLock) {
if (closePending || (fd == null)) {
return true;
} else {
return false;
}
}
}
返回超时时长
public int getTimeout() {
return timeout;
}
预关闭套接字(不释放文件描述符和资源
private void socketPreClose() throws IOException {
socketClose0(true);
}
关闭套接字(释放资源和描述符
protected void socketClose() throws IOException {
socketClose0(false);
}
接下来是一些需要完成的方法,方法用途可以通过名称判断:
abstract void socketCreate(boolean isServer) throws IOException;
abstract void socketConnect(InetAddress address, int port, int timeout)
throws IOException;
abstract void socketBind(InetAddress address, int port)
throws IOException;
abstract void socketListen(int count)
throws IOException;
abstract void socketAccept(SocketImpl s)
throws IOException;
abstract int socketAvailable()
throws IOException;
abstract void socketClose0(boolean useDeferredClose)
throws IOException;
abstract void socketShutdown(int howto)
throws IOException;
abstract void socketSetOption(int cmd, boolean on, Object value)
throws SocketException;
abstract int socketGetOption(int opt, Object iaContainerObj) throws SocketException;
abstract void socketSendUrgentData(int data)
throws IOException;
该类含有如下的静态代码块(初始化网络库的运行环境
static {
java.security.AccessController.doPrivileged(//无视安全检查
new java.security.PrivilegedAction<Void>() {
public Void run() {
System.loadLibrary("net");
return null;
}
});
}
该类属于Socket的基本模版,主要为套接字定下了一个大的框架,计算机网络知识中的一些操作在这里也得到体现,如紧急提交标志位等,该类的阅读需要一定的计算机网络基础,否则可能难以准确理解实际意义。