?

?

9、public final static int IP_TOS = 0x3;

? ? ? 这个参数是用来控制IP头中的TOS字段的，是用来控制和优化IP包的路径的，在Socket源代码里有一个设置的方法：

? ? ?

?

/**
? ? * Sets traffic class or type-of-service octet in the IP
? ? * header for packets sent from this Socket.
? ? * As the underlying network implementation may ignore this
? ? * value applications should consider it a hint.
? ? *
? ? *

The tc must be in the range 0 <= tc <=
? ? * 255 or an IllegalArgumentException will be thrown.
? ? *

Notes:
? ? *

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 :-
? ? *

? ? *

? ? *
• IPTOS_LOWCOST (0x02)

? ? *
• IPTOS_RELIABILITY (0x04)

? ? *
• IPTOS_THROUGHPUT (0x08)

? ? *
• IPTOS_LOWDELAY (0x10)

? ? *

? ? * 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.
? ? *
? ? * @param tc? ? ? ? an int value for the bitset.
? ? * @throws SocketException if there is an error setting the
? ? * traffic class or type-of-service
? ? * @since 1.4
? ? * @see #getTrafficClass
? ? */
? ? 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");
? ? ? ? getImpl().setOption(SocketOptions.IP_TOS, new Integer(tc));
? ? }

?

?从源代码的注释看，TOS设置了是否生效，和底层的操作系统的实现有关。应用程序无法保证TOS的变更会对socket连接产生影响。个人认为，TOS在一般情况下用不到。

?

10、public final static int SO_LINGER = 0x0080;

? ? ? 先看Socket源代码：

? ?

?

/**
? ? * Enable/disable SO_LINGER with the specified linger time in seconds.
? ? * The maximum timeout value is platform specific.
? ? *
? ? * The setting only affects socket close.
? ? *
? ? * @param on? ? whether or not to linger on.
? ? * @param linger how long to linger for, if on is true.
? ? * @exception SocketException if there is an error
? ? * in the underlying protocol, such as a TCP error.
? ? * @exception IllegalArgumentException if the linger value is negative.
? ? * @since JDK1.1
? ? * @see #getSoLinger()
? ? */
? ? 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));
? ? }
? ? }

? ? ? 这个字段对Socket的close方法产生影响，当这个字段设置为false时，close会立即执行并返回，如果这时仍然有未被送出的数据包，那么这些数据包将被丢弃。如果设置为True时，有一个延迟时间可以设置。这个延迟时间就是close真正执行所有等待的时间，最大为65535。?

11、public final static int SO_TIMEOUT = 0x1006;?