java.lang.Object java.net.Socket
public class Socket
This class implements client sockets (also called just "sockets"). A socket is an endpoint for communication between two machines.
The actual work of the socket is performed by an instance of the SocketImpl class. An application, by changing the socket factory that creates the socket implementation, can configure itself to create sockets appropriate to the local firewall.
Constructor Summary | |
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Socket
() Creates an unconnected socket, with the system-default type of SocketImpl. |
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Socket
(
InetAddress
address, int port) Creates a stream socket and connects it to the specified port number at the specified IP address. |
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Socket
(
InetAddress
host, int port, boolean stream) Deprecated. Use DatagramSocket instead for UDP transport. |
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Socket
(
InetAddress
address, int port,
InetAddress
localAddr, int localPort) Creates a socket and connects it to the specified remote address on the specified remote port. |
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Socket
(
Proxy
proxy) Creates an unconnected socket, specifying the type of proxy, if any, that should be used regardless of any other settings. |
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protected |
Socket
(
SocketImpl
impl) Creates an unconnected Socket with a user-specified SocketImpl. |
Socket
(
String
host, int port) Creates a stream socket and connects it to the specified port number on the named host. |
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Socket
(
String
host, int port, boolean stream) Deprecated. Use DatagramSocket instead for UDP transport. |
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Socket
(
String
host, int port,
InetAddress
localAddr, int localPort) Creates a socket and connects it to the specified remote host on the specified remote port. |
Method Summary | |
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void |
bind
(
SocketAddress
bindpoint) Binds the socket to a local address. |
void |
close
() Closes this socket. |
void |
connect
(
SocketAddress
endpoint) Connects this socket to the server. |
void |
connect
(
SocketAddress
endpoint, int timeout) Connects this socket to the server with a specified timeout value. |
SocketChannel |
getChannel
() Returns the unique SocketChannel object associated with this socket, if any. |
InetAddress |
getInetAddress
() Returns the address to which the socket is connected. |
InputStream |
getInputStream
() Returns an input stream for this socket. |
boolean |
getKeepAlive
() Tests if SO_KEEPALIVE is enabled. |
InetAddress |
getLocalAddress
() Gets the local address to which the socket is bound. |
int |
getLocalPort
() Returns the local port to which this socket is bound. |
SocketAddress |
getLocalSocketAddress
() Returns the address of the endpoint this socket is bound to, or null if it is not bound yet. |
boolean |
getOOBInline
() Tests if OOBINLINE is enabled. |
OutputStream |
getOutputStream
() Returns an output stream for this socket. |
int |
getPort
() Returns the remote port to which this socket is connected. |
int |
getReceiveBufferSize
() Gets the value of the SO_RCVBUF option for this Socket , that is the buffer size used by the platform for input on this Socket . |
SocketAddress |
getRemoteSocketAddress
() Returns the address of the endpoint this socket is connected to, or null if it is unconnected. |
boolean |
getReuseAddress
() Tests if SO_REUSEADDR is enabled. |
int |
getSendBufferSize
() Get value of the SO_SNDBUF option for this Socket , that is the buffer size used by the platform for output on this Socket . |
int |
getSoLinger
() Returns setting for SO_LINGER. |
int |
getSoTimeout
() Returns setting for SO_TIMEOUT. |
boolean |
getTcpNoDelay
() Tests if TCP_NODELAY is enabled. |
int |
getTrafficClass
() Gets traffic class or type-of-service in the IP header for packets sent from this Socket |
boolean |
isBound
() Returns the binding state of the socket. |
boolean |
isClosed
() Returns the closed state of the socket. |
boolean |
isConnected
() Returns the connection state of the socket. |
boolean |
isInputShutdown
() Returns whether the read-half of the socket connection is closed. |
boolean |
isOutputShutdown
() Returns whether the write-half of the socket connection is closed. |
void |
sendUrgentData
(int data) Send one byte of urgent data on the socket. |
void |
setKeepAlive
(boolean on) Enable/disable SO_KEEPALIVE. |
void |
setOOBInline
(boolean on) Enable/disable OOBINLINE (receipt of TCP urgent data) By default, this option is disabled and TCP urgent data received on a socket is silently discarded. |
void |
setPerformancePreferences
(int connectionTime, int latency, int bandwidth) Sets performance preferences for this socket. |
void |
setReceiveBufferSize
(int size) Sets the SO_RCVBUF option to the specified value for this Socket . |
void |
setReuseAddress
(boolean on) Enable/disable the SO_REUSEADDR socket option. |
void |
setSendBufferSize
(int size) Sets the SO_SNDBUF option to the specified value for this Socket . |
static void |
setSocketImplFactory
(
SocketImplFactory
fac) Sets the client socket implementation factory for the application. |
void |
setSoLinger
(boolean on, int linger) Enable/disable SO_LINGER with the specified linger time in seconds. |
void |
setSoTimeout
(int timeout) Enable/disable SO_TIMEOUT with the specified timeout, in milliseconds. |
void |
setTcpNoDelay
(boolean on) Enable/disable TCP_NODELAY (disable/enable Nagle's algorithm). |
void |
setTrafficClass
(int tc) Sets traffic class or type-of-service octet in the IP header for packets sent from this Socket. |
void |
shutdownInput
() Places the input stream for this socket at "end of stream". |
void |
shutdownOutput
() Disables the output stream for this socket. |
String |
toString
() Converts this socket to a String. |
Methods inherited from class java.lang. Object |
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clone , equals , finalize , getClass , hashCode , notify , notifyAll , wait , wait , wait |
Constructor Detail |
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public Socket()
public Socket(Proxy proxy)
If there is a security manager, its checkConnect method is called with the proxy host address and port number as its arguments. This could result in a SecurityException.
Examples:
protected Socket(SocketImpl impl) throws SocketException
public Socket(String host, int port) throws UnknownHostException, IOException
If the specified host is null it is the equivalent of specifying the address as InetAddress.getByName (null) . In other words, it is equivalent to specifying an address of the loopback interface.
If the application has specified a server socket factory, that factory's createSocketImpl method is called to create the actual socket implementation. Otherwise a "plain" socket is created.
If there is a security manager, its checkConnect method is called with the host address and port as its arguments. This could result in a SecurityException.
public Socket(InetAddress address, int port) throws IOException
If the application has specified a socket factory, that factory's createSocketImpl method is called to create the actual socket implementation. Otherwise a "plain" socket is created.
If there is a security manager, its checkConnect method is called with the host address and port as its arguments. This could result in a SecurityException.
public Socket(String host, int port, InetAddress localAddr, int localPort) throws IOException
If the specified host is null it is the equivalent of specifying the address as InetAddress.getByName (null) . In other words, it is equivalent to specifying an address of the loopback interface.
If there is a security manager, its checkConnect method is called with the host address and port as its arguments. This could result in a SecurityException.
public Socket(InetAddress address, int port, InetAddress localAddr, int localPort) throws IOException
If there is a security manager, its checkConnect method is called with the host address and port as its arguments. This could result in a SecurityException.
@Deprecated public Socket(String host, int port, boolean stream) throws IOException
If the specified host is null it is the equivalent of specifying the address as InetAddress.getByName (null) . In other words, it is equivalent to specifying an address of the loopback interface.
If the stream argument is true, this creates a stream socket. If the stream argument is false, it creates a datagram socket.
If the application has specified a server socket factory, that factory's createSocketImpl method is called to create the actual socket implementation. Otherwise a "plain" socket is created.
If there is a security manager, its checkConnect method is called with the host address and port as its arguments. This could result in a SecurityException.
If a UDP socket is used, TCP/IP related socket options will not apply.
@Deprecated public Socket(InetAddress host, int port, boolean stream) throws IOException
If the stream argument is true, this creates a stream socket. If the stream argument is false, it creates a datagram socket.
If the application has specified a server socket factory, that factory's createSocketImpl method is called to create the actual socket implementation. Otherwise a "plain" socket is created.
If there is a security manager, its checkConnect method is called with host.getHostAddress() and port as its arguments. This could result in a SecurityException.
If UDP socket is used, TCP/IP related socket options will not apply.
Method Detail |
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public void connect(SocketAddress endpoint) throws IOException
public void connect(SocketAddress endpoint, int timeout) throws IOException
public void bind(SocketAddress bindpoint) throws IOException
If the address is null, then the system will pick up an ephemeral port and a valid local address to bind the socket.
public InetAddress getInetAddress()
public InetAddress getLocalAddress()
public int getPort()
public int getLocalPort()
public SocketAddress getRemoteSocketAddress()
public SocketAddress getLocalSocketAddress()
public SocketChannel getChannel()
A socket will have a channel if, and only if, the channel itself was created via the SocketChannel.open or ServerSocketChannel.accept methods.
public InputStream getInputStream() throws IOException
If this socket has an associated channel then the resulting input stream delegates all of its operations to the channel. If the channel is in non-blocking mode then the input stream's read operations will throw an IllegalBlockingModeException .
Under abnormal conditions the underlying connection may be broken by the remote host or the network software (for example a connection reset in the case of TCP connections). When a broken connection is detected by the network software the following applies to the returned input stream :-
The network software may discard bytes that are buffered by the socket. Bytes that aren't discarded by the network software can be read using read .
If there are no bytes buffered on the socket, or all buffered bytes have been consumed by read , then all subsequent calls to read will throw an IOException .
If there are no bytes buffered on the socket, and the socket has not been closed using close , then available will return 0.
public OutputStream getOutputStream() throws IOException
If this socket has an associated channel then the resulting output stream delegates all of its operations to the channel. If the channel is in non-blocking mode then the output stream's write operations will throw an IllegalBlockingModeException .
public void setTcpNoDelay(boolean on) throws SocketException
public boolean getTcpNoDelay() throws SocketException
public void setSoLinger(boolean on, int linger) throws SocketException
public int getSoLinger() throws SocketException
public void sendUrgentData(int data) throws IOException
public void setOOBInline(boolean on) throws SocketException
Note, only limited support is provided for handling incoming urgent data. In particular, no notification of incoming urgent data is provided and there is no capability to distinguish between normal data and urgent data unless provided by a higher level protocol.
public boolean getOOBInline() throws SocketException
public void setSoTimeout(int timeout) throws SocketException
public int getSoTimeout() throws SocketException
public void setSendBufferSize(int size) throws SocketException
Because SO_SNDBUF is a hint, applications that want to verify what size the buffers were set to should call getSendBufferSize() .
public int getSendBufferSize() throws SocketException
public void setReceiveBufferSize(int size) throws SocketException
Increasing the receive buffer size can increase the performance of network I/O for high-volume connection, while decreasing it can help reduce the backlog of incoming data.
Because SO_RCVBUF is a hint, applications that want to verify what size the buffers were set to should call getReceiveBufferSize() .
The value of SO_RCVBUF is also used to set the TCP receive window that is advertized to the remote peer. Generally, the window size can be modified at any time when a socket is connected. However, if a receive window larger than 64K is required then this must be requested before the socket is connected to the remote peer. There are two cases to be aware of:
public int getReceiveBufferSize() throws SocketException
public void setKeepAlive(boolean on) throws SocketException
public boolean getKeepAlive() throws SocketException
public void setTrafficClass(int tc) throws SocketException
The tc must be in the range 0 <= tc <= 255 or an IllegalArgumentException will be thrown.
Notes:
For
for
Internet Protocol v4 the value consists of an octet with precedence and TOS fields as detailed in RFC 1349. The TOS field is bitset created by bitwise-or'ing values such the following :-
Setting bits in the precedence field may result in a SocketException indicating that the operation is not permitted.
As RFC 1122 section 4.2.4.2 indicates, a compliant TCP implementation should, but is not required to, let application change the TOS field during the lifetime of a connection. So whether the type-of-service field can be changed after the TCP connection has been established depends on the implementation in the underlying platform. Applications should not assume that they can change the TOS field after the connection.
for Internet Protocol v6 tc is the value that would be placed into the sin6_flowinfo field of the IP header.
For Internet Protocol v6 tc is the value that would be placed into the sin6_flowinfo field of the IP header.
public int getTrafficClass() throws SocketException
As the underlying network implementation may ignore the traffic class or type-of-service set using setTrafficClass(int) this method may return a different value than was previously set using the setTrafficClass(int) method on this Socket.
public void setReuseAddress(boolean on) throws SocketException
When a TCP connection is closed the connection may remain in a timeout state for a period of time after the connection is closed (typically known as the TIME_WAIT state or 2MSL wait state). For applications using a well known socket address or port it may not be possible to bind a socket to the required SocketAddress if there is a connection in the timeout state involving the socket address or port.
Enabling SO_REUSEADDR prior to binding the socket using bind(SocketAddress) allows the socket to be bound even though a previous connection is in a timeout state.
When a Socket is created the initial setting of SO_REUSEADDR is disabled.
The behaviour when SO_REUSEADDR is enabled or disabled after a socket is bound (See isBound() ) is not defined.
public boolean getReuseAddress() throws SocketException
public void close() throws IOException
Any thread currently blocked in an I/O operation upon this socket will throw a SocketException .
Once a socket has been closed, it is not available for further networking use (i.e. can't be reconnected or rebound). A new socket needs to be created.
If this socket has an associated channel then the channel is closed as well.
public void shutdownInput() throws IOException
If you read from a socket input stream after invoking shutdownInput() on the socket, the stream will return EOF.
public void shutdownOutput() throws IOException
public String toString()
public boolean isConnected()
public boolean isBound()
public boolean isClosed()
public boolean isInputShutdown()
public boolean isOutputShutdown()
public static void setSocketImplFactory(SocketImplFactory fac) throws IOException
When an application creates a new client socket, the socket implementation factory's createSocketImpl method is called to create the actual socket implementation.
Passing null to the method is a no-op unless the factory was already set.
If there is a security manager, this method first calls the security manager's checkSetFactory method to ensure the operation is allowed. This could result in a SecurityException.
public void setPerformancePreferences(int connectionTime, int latency, int bandwidth)
Sockets use the TCP/IP protocol by default. Some implementations may offer alternative protocols which have different performance characteristics than TCP/IP. This method allows the application to express its own preferences as to how these tradeoffs should be made when the implementation chooses from the available protocols.
Performance preferences are described by three integers whose values indicate the relative importance of short connection time, low latency, and high bandwidth. The absolute values of the integers are irrelevant; in order to choose a protocol the values are simply compared, with larger values indicating stronger preferences. Negative values represent a lower priority than positive values. If the application prefers short connection time over both low latency and high bandwidth, for example, then it could invoke this method with the values (1, 0, 0) . If the application prefers high bandwidth above low latency, and low latency above short connection time, then it could invoke this method with the values (0, 1, 2) .
Invoking this method after this socket has been connected will have no effect.