Socket 类表示通信双方中的客户端，用于呼叫远端机器上的一个端口，主动向服务器端发送数据（当连接建立后也能接收数据）。下面我将从源码的角度来介绍Socket类的内部原理及其方法。
二、Socket类源码介绍首先，Socket类实现了java.io.Closeable的接口
public
class Socket implements java.io.Closeable {
}
下面定义了一些Socket的一些状态
private boolean created = false;
private boolean bound = false;
private boolean connected = false;
private boolean closed = false;
private Object closeLock = new Object();
private boolean shutIn = false;
private boolean shutOut = false;
Socket 的实现
SocketImpl impl;
确定是否使用旧的 Socket
private boolean oldImpl = false;
创建一个未连接的Socket
public Socket() {
setImpl();
}
Socket 的实现类，通过Proxy代理实现
public Socket(Proxy proxy) {
// Create a copy of Proxy as a security measure
if (proxy == null) {
throw new IllegalArgumentException("Invalid Proxy");
}
Proxy p = proxy == Proxy.NO_PROXY ? Proxy.NO_PROXY
: sun.net.ApplicationProxy.create(proxy);
Proxy.Type type = p.type();
if (type == Proxy.Type.SOCKS || type == Proxy.Type.HTTP) {
SecurityManager security = System.getSecurityManager();
InetSocketAddress epoint = (InetSocketAddress) p.address();
if (epoint.getAddress() != null) {
checkAddress (epoint.getAddress(), "Socket");
}
if (security != null) {
if (epoint.isUnresolved())
epoint = new InetSocketAddress(epoint.getHostName(), epoint.getPort());
if (epoint.isUnresolved())
security.checkConnect(epoint.getHostName(), epoint.getPort());
else
security.checkConnect(epoint.getAddress().getHostAddress(),
epoint.getPort());
}
impl = type == Proxy.Type.SOCKS ? new SocksSocketImpl(p)
: new HttpConnectSocketImpl(p);
impl.setSocket(this);
} else {
if (p == Proxy.NO_PROXY) {
if (factory == null) {
impl = new PlainSocketImpl();
impl.setSocket(this);
} else
setImpl();
} else
throw new IllegalArgumentException("Invalid Proxy");
}
}
使用用户指定的 SocketImpl 创建一个未连接的 Socket。
protected Socket(SocketImpl impl) throws SocketException {
this.impl = impl;
if (impl != null) {
checkOldImpl();
this.impl.setSocket(this);
}
}
Socket使用代理器和端口号篇port
public Socket(String host, int port)
throws UnknownHostException, IOException
{
this(host != null ? new InetSocketAddress(host, port) :
new InetSocketAddress(InetAddress.getByName(null), port),
(SocketAddress) null, true);
}
利用网络地址和端口号创建Socket
public Socket(InetAddress address, int port) throws IOException {
this(address != null ? new InetSocketAddress(address, port) : null,
(SocketAddress) null, true);
}
创建本地和联网的Socket
public Socket(String host, int port, InetAddress localAddr,
int localPort) throws IOException {
this(host != null ? new InetSocketAddress(host, port) :
new InetSocketAddress(InetAddress.getByName(null), port),
new InetSocketAddress(localAddr, localPort), true);
}
public Socket(InetAddress address, int port, InetAddress localAddr,
int localPort) throws IOException {
this(address != null ? new InetSocketAddress(address, port) : null,
new InetSocketAddress(localAddr, localPort), true);
}
定义实现本地连接和本地数据流
private Socket(SocketAddress address, SocketAddress localAddr,
boolean stream) throws IOException {
setImpl();
// backward compatibility
if (address == null)
throw new NullPointerException();
try {
createImpl(stream);
if (localAddr != null)
bind(localAddr);
connect(address);
} catch (IOException | IllegalArgumentException | SecurityException e) {
try {
close();
} catch (IOException ce) {
e.addSuppressed(ce);
}
throw e;
}
}
创建套接字实现。
void createImpl(boolean stream) throws SocketException {
if (impl == null)
setImpl();
try {
impl.create(stream);
created = true;
} catch (IOException e) {
throw new SocketException(e.getMessage());
}
}
检查旧的嵌套字
private void checkOldImpl() {
if (impl == null)
return;
// SocketImpl.connect() is a protected method, therefore we need to use
// getDeclaredMethod, therefore we need permission to access the member
oldImpl = AccessController.doPrivileged
(new PrivilegedAction() {
public Boolean run() {
Class clazz = impl.getClass();
while (true) {
try {
clazz.getDeclaredMethod("connect", SocketAddress.class, int.class);
return Boolean.FALSE;
} catch (NoSuchMethodException e) {
clazz = clazz.getSuperclass();
// java.net.SocketImpl class will always have this abstract method.
// If we have not found it by now in the hierarchy then it does not
// exist, we are an old style impl.
if (clazz.equals(java.net.SocketImpl.class)) {
return Boolean.TRUE;
}
}
}
}
});
}
设置网络嵌套字
void setImpl() {
if (factory != null) {
impl = factory.createSocketImpl();
checkOldImpl();
} else {
// No need to do a checkOldImpl() here, we know it's an up to date
// SocketImpl!
impl = new SocksSocketImpl();
}
if (impl != null)
impl.setSocket(this);
}
获取网络嵌套字
SocketImpl getImpl() throws SocketException {
if (!created)
createImpl(true);
return impl;
}
定义连接服务端
public void connect(SocketAddress endpoint) throws IOException {
connect(endpoint, 0);
}
定义连接并设置有超时时间
public void connect(SocketAddress endpoint, int timeout) throws IOException {
if (endpoint == null)
throw new IllegalArgumentException("connect: The address can't be null");
if (timeout < 0)
throw new IllegalArgumentException("connect: timeout can't be negative");
if (isClosed())
throw new SocketException("Socket is closed");
if (!oldImpl && isConnected())
throw new SocketException("already connected");
if (!(endpoint instanceof InetSocketAddress))
throw new IllegalArgumentException("Unsupported address type");
InetSocketAddress epoint = (InetSocketAddress) endpoint;
InetAddress addr = epoint.getAddress ();
int port = epoint.getPort();
checkAddress(addr, "connect");
SecurityManager security = System.getSecurityManager();
if (security != null) {
if (epoint.isUnresolved())
security.checkConnect(epoint.getHostName(), port);
else
security.checkConnect(addr.getHostAddress(), port);
}
if (!created)
createImpl(true);
if (!oldImpl)
impl.connect(epoint, timeout);
else if (timeout == 0) {
if (epoint.isUnresolved())
impl.connect(addr.getHostName(), port);
else
impl.connect(addr, port);
} else
throw new UnsupportedOperationException("SocketImpl.connect(addr, timeout)");
connected = true;
bound = true;
}
将嵌套字绑定本地
public void bind(SocketAddress bindpoint) throws IOException {
if (isClosed())
throw new SocketException("Socket is closed");
if (!oldImpl && isBound())
throw new SocketException("Already bound");
if (bindpoint != null && (!(bindpoint instanceof InetSocketAddress)))
throw new IllegalArgumentException("Unsupported address type");
InetSocketAddress epoint = (InetSocketAddress) bindpoint;
if (epoint != null && epoint.isUnresolved())
throw new SocketException("Unresolved address");
if (epoint == null) {
epoint = new InetSocketAddress(0);
}
InetAddress addr = epoint.getAddress();
int port = epoint.getPort();
checkAddress (addr, "bind");
SecurityManager security = System.getSecurityManager();
if (security != null) {
security.checkListen(port);
}
getImpl().bind (addr, port);
bound = true;
}
检查地址
private void checkAddress (InetAddress addr, String op) {
if (addr == null) {
return;
}
if (!(addr instanceof Inet4Address || addr instanceof Inet6Address)) {
throw new IllegalArgumentException(op + ": invalid address type");
}
}
定义接受请求
final void postAccept() {
connected = true;
created = true;
bound = true;
}
下面定义实现状态设置
void setCreated() {
created = true;
}
void setBound() {
bound = true;
}
void setConnected() {
connected = true;
}
获取网络地址
public InetAddress getInetAddress() {
if (!isConnected())
return null;
try {
return getImpl().getInetAddress();
} catch (SocketException e) {
}
return null;
}
获取本地地址
public InetAddress getLocalAddress() {
// This is for backward compatibility
if (!isBound())
return InetAddress.anyLocalAddress();
InetAddress in = null;
try {
in = (InetAddress) getImpl().getOption(SocketOptions.SO_BINDADDR);
SecurityManager sm = System.getSecurityManager();
if (sm != null)
sm.checkConnect(in.getHostAddress(), -1);
if (in.isAnyLocalAddress()) {
in = InetAddress.anyLocalAddress();
}
} catch (SecurityException e) {
in = InetAddress.getLoopbackAddress();
} catch (Exception e) {
in = InetAddress.anyLocalAddress(); // "0.0.0.0"
}
return in;
}
返回此套接字连接到的远程端口号。
public int getPort() {
if (!isConnected())
return 0;
try {
return getImpl().getPort();
} catch (SocketException e) {
// Shouldn't happen as we're connected
}
return -1;
}
获取本地端口号
public int getLocalPort() {
if (!isBound())
return -1;
try {
return getImpl().getLocalPort();
} catch(SocketException e) {
// shouldn't happen as we're bound
}
return -1;
}
获取远程嵌套字地址
public SocketAddress getRemoteSocketAddress() {
if (!isConnected())
return null;
return new InetSocketAddress(getInetAddress(), getPort());
}
获取本地嵌套字地址
public SocketAddress getLocalSocketAddress() {
if (!isBound())
return null;
return new InetSocketAddress(getLocalAddress(), getLocalPort());
}
获取嵌套字的传输管道
public SocketChannel getChannel() {
return null;
}
获取输入流函数
public InputStream getInputStream() throws IOException {
if (isClosed())
throw new SocketException("Socket is closed");
if (!isConnected())
throw new SocketException("Socket is not connected");
if (isInputShutdown())
throw new SocketException("Socket input is shutdown");
final Socket s = this;
InputStream is = null;
try {
is = AccessController.doPrivileged(
new PrivilegedExceptionAction() {
public InputStream run() throws IOException {
return impl.getInputStream();
}
});
} catch (java.security.PrivilegedActionException e) {
throw (IOException) e.getException();
}
return is;
}
获取输出流函数
public OutputStream getOutputStream() throws IOException {
if (isClosed())
throw new SocketException("Socket is closed");
if (!isConnected())
throw new SocketException("Socket is not connected");
if (isOutputShutdown())
throw new SocketException("Socket output is shutdown");
final Socket s = this;
OutputStream os = null;
try {
os = AccessController.doPrivileged(
new PrivilegedExceptionAction() {
public OutputStream run() throws IOException {
return impl.getOutputStream();
}
});
} catch (java.security.PrivilegedActionException e) {
throw (IOException) e.getException();
}
return os;
}
设置无延时TCP传输
public void setTcpNoDelay(boolean on) throws SocketException {
if (isClosed())
throw new SocketException("Socket is closed");
getImpl().setOption(SocketOptions.TCP_NODELAY, Boolean.valueOf(on));
}
获取TCP无延时服务
public boolean getTcpNoDelay() throws SocketException {
if (isClosed())
throw new SocketException("Socket is closed");
return ((Boolean) getImpl().getOption(SocketOptions.TCP_NODELAY)).booleanValue();
}
设置延时等待
public void setSoLinger(boolean on, int linger) throws SocketException {
if (isClosed())
throw new SocketException("Socket is closed");
if (!on) {
getImpl().setOption(SocketOptions.SO_LINGER, new Boolean(on));
} else {
if (linger < 0) {
throw new IllegalArgumentException("invalid value for SO_LINGER");
}
if (linger > 65535)
linger = 65535;
getImpl().setOption(SocketOptions.SO_LINGER, new Integer(linger));
}
}
获取延时等待
public int getSoLinger() throws SocketException {
if (isClosed())
throw new SocketException("Socket is closed");
Object o = getImpl().getOption(SocketOptions.SO_LINGER);
if (o instanceof Integer) {
return ((Integer) o).intValue();
} else {
return -1;
}
}
发送紧急信息
public void sendUrgentData (int data) throws IOException {
if (!getImpl().supportsUrgentData ()) {
throw new SocketException ("Urgent data not supported");
}
getImpl().sendUrgentData (data);
}
设置OOB内联
public void setOOBInline(boolean on) throws SocketException {
if (isClosed())
throw new SocketException("Socket is closed");
getImpl().setOption(SocketOptions.SO_OOBINLINE, Boolean.valueOf(on));
}
获取OOB（面向对象）内联
public boolean getOOBInline() throws SocketException {
if (isClosed())
throw new SocketException("Socket is closed");
return ((Boolean) getImpl().getOption(SocketOptions.SO_OOBINLINE)).booleanValue();
}
设置超时时间
public synchronized void setSoTimeout(int timeout) throws SocketException {
if (isClosed())
throw new SocketException("Socket is closed");
if (timeout < 0)
throw new IllegalArgumentException("timeout can't be negative");
getImpl().setOption(SocketOptions.SO_TIMEOUT, new Integer(timeout));
}
获取超时时间
public synchronized int getSoTimeout() throws SocketException {
if (isClosed())
throw new SocketException("Socket is closed");
Object o = getImpl().getOption(SocketOptions.SO_TIMEOUT);
if (o instanceof Integer) {
return ((Integer) o).intValue();
} else {
return 0;
}
}
设置发送缓冲区大小
public synchronized void setSendBufferSize(int size)
throws SocketException{
if (!(size > 0)) {
throw new IllegalArgumentException("negative send size");
}
if (isClosed())
throw new SocketException("Socket is closed");
getImpl().setOption(SocketOptions.SO_SNDBUF, new Integer(size));
}
获取发送缓冲区大小
public synchronized int getSendBufferSize() throws SocketException {
if (isClosed())
throw new SocketException("Socket is closed");
int result = 0;
Object o = getImpl().getOption(SocketOptions.SO_SNDBUF);
if (o instanceof Integer) {
result = ((Integer)o).intValue();
}
return result;
}
设置获取缓冲区的大小
public synchronized void setReceiveBufferSize(int size)
throws SocketException{
if (size <= 0) {
throw new IllegalArgumentException("invalid receive size");
}
if (isClosed())
throw new SocketException("Socket is closed");
getImpl().setOption(SocketOptions.SO_RCVBUF, new Integer(size));
}
获取获取缓冲区大小
public synchronized int getReceiveBufferSize()
throws SocketException{
if (isClosed())
throw new SocketException("Socket is closed");
int result = 0;
Object o = getImpl().getOption(SocketOptions.SO_RCVBUF);
if (o instanceof Integer) {
result = ((Integer)o).intValue();
}
return result;
}
设置保持存活函数
public void setKeepAlive(boolean on) throws SocketException {
if (isClosed())
throw new SocketException("Socket is closed");
getImpl().setOption(SocketOptions.SO_KEEPALIVE, Boolean.valueOf(on));
}
获取保持存活函数
public boolean getKeepAlive() throws SocketException {
if (isClosed())
throw new SocketException("Socket is closed");
return ((Boolean) getImpl().getOption(SocketOptions.SO_KEEPALIVE)).booleanValue();
}
设置Socket传输通道大小
public void setTrafficClass(int tc) throws SocketException {
if (tc < 0 || tc > 255)
throw new IllegalArgumentException("tc is not in range 0 -- 255");
if (isClosed())
throw new SocketException("Socket is closed");
try {
getImpl().setOption(SocketOptions.IP_TOS, tc);
} catch (SocketException se) {
// not supported if socket already connected
// Solaris returns error in such cases
if(!isConnected())
throw se;
}
}
获取Socket传输通道大小
public int getTrafficClass() throws SocketException {
return ((Integer) (getImpl().getOption(SocketOptions.IP_TOS))).intValue();
}
定义设置重用地址方法
public void setReuseAddress(boolean on) throws SocketException {
if (isClosed())
throw new SocketException("Socket is closed");
getImpl().setOption(SocketOptions.SO_REUSEADDR, Boolean.valueOf(on));
}
定义获取重用方法
public boolean getReuseAddress() throws SocketException {
if (isClosed())
throw new SocketException("Socket is closed");
return ((Boolean) (getImpl().getOption(SocketOptions.SO_REUSEADDR))).booleanValue();
}
定义Socket类的关闭
public synchronized void close() throws IOException {
synchronized(closeLock) {
if (isClosed())
return;
if (created)
impl.close();
closed = true;
}
}
这个方法应放置于文件末尾，用于关闭嵌套字的输入
public void shutdownInput() throws IOException
{
if (isClosed())
throw new SocketException("Socket is closed");
if (!isConnected())
throw new SocketException("Socket is not connected");
if (isInputShutdown())
throw new SocketException("Socket input is already shutdown");
getImpl().shutdownInput();
shutIn = true;
}
这个方法应放置于文件末尾，用于关闭嵌套字的输出
public void shutdownOutput() throws IOException
{
if (isClosed())
throw new SocketException("Socket is closed");
if (!isConnected())
throw new SocketException("Socket is not connected");
if (isOutputShutdown())
throw new SocketException("Socket output is already shutdown");
getImpl().shutdownOutput();
shutOut = true;
}
将Socket信息转化为字符串
public String toString() {
try {
if (isConnected())
return "Socket[addr=" + getImpl().getInetAddress() +
",port=" + getImpl().getPort() +
",localport=" + getImpl().getLocalPort() + "]";
} catch (SocketException e) {
}
return "Socket[unconnected]";
}
判断是否处于连接状态
public boolean isConnected() {
// Before 1.3 Sockets were always connected during creation
return connected || oldImpl;
}
判断是否处于绑定状态
public boolean isBound() {
// Before 1.3 Sockets were always bound during creation
return bound || oldImpl;
}
判断是否关闭状态
public boolean isClosed() {
synchronized(closeLock) {
return closed;
}
}
判断是否是输入关闭状态
public boolean isInputShutdown() {
return shutIn;
}
判断是否是输出关闭状态
public boolean isOutputShutdown() {
return shutOut;
}
定义所有客户端套接字的工厂
private static SocketImplFactory factory = null;
定义设置所有客户端套接字的工厂
public static synchronized void setSocketImplFactory(SocketImplFactory fac)
throws IOException
{
if (factory != null) {
throw new SocketException("factory already defined");
}
SecurityManager security = System.getSecurityManager();
if (security != null) {
security.checkSetFactory();
}
factory = fac;
}
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