在MulticastSocket的源代碼里有設(shè)置多播的方法：

public void setInterface(InetAddress inf) throwsSocketException {

if(isClosed()) {

throw new SocketException("Socket is closed");

}

checkAddress(inf, "setInterface");

synchronized(infLock) {

getImpl().setOption(SocketOptions.IP_MULTICAST_IF, inf);

infAddress =inf;

}

}

7、public final static int IP_MULTICAST_IF2 = 0x1f;

這個字段的效果和上面的是一樣的，只是擴展支持IPV6

8、public final static int IP_MULTICAST_LOOP = 0x12;

用來設(shè)置本地回環(huán)接口的多播特性，在MulticastSocket源代碼中有相關(guān)方法：

/*** Disable/Enable local loopback of multicast datagrams

* The option is used by the platform's networking code as a hint

* for setting whether multicast data will be looped back to

* the local socket.

*

*

Because this option is a hint, applications that want to

* verify what loopback mode is set to should call

* {@link#getLoopbackMode()}

* @paramdisable true to disable the LoopbackMode

* @throwsSocketException if an error occurs while setting the value

* @since1.4

* @see#getLoopbackMode

*/

public void setLoopbackMode(boolean disable) throwsSocketException {

getImpl().setOption(SocketOptions.IP_MULTICAST_LOOP, Boolean.valueOf(disable));

}

9、public final static int IP_TOS = 0x3;

這個參數(shù)是用來控制IP頭中的TOS字段的，是用來控制和優(yōu)化IP包的路徑的，在Socket源代碼里有一個設(shè)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)

*

* The last low order bit is always ignored as this

* corresponds to the MBZ (must be zero) bit.

*

* 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.

*

* @paramtc an int value for the bitset.

* @throwsSocketException if there is an error setting the

* traffic class or type-of-service

* @since1.4

* @see#getTrafficClass

*/

public void setTrafficClass(int tc) throwsSocketException {

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, newInteger(tc));

}

從源代碼的注釋看，TOS設(shè)置了是否生效，和底層的操作系統(tǒng)的實現(xiàn)有關(guān)。應(yīng)用程序無法保證TOS的變更會對socket連接產(chǎn)生影響。個人認為，TOS在一般情況下用不到。

10、public final static int SO_LINGER = 0x0080;

先看Socket源代碼：

/*** Enable/disable SO_LINGER with the specified linger time in seconds.

* The maximum timeout value is platform specific.

*

* The setting only affects socket close.

*

* @paramon whether or not to linger on.

* @paramlinger how long to linger for, if on is true.

* @exceptionSocketException if there is an error

* in the underlying protocol, such as a TCP error.

* @exceptionIllegalArgumentException if the linger value is negative.

* @sinceJDK1.1

* @see#getSoLinger()

*/

public void setSoLinger(boolean on, int linger) throwsSocketException {

if(isClosed())

throw new SocketException("Socket is closed");

if (!on) {

getImpl().setOption(SocketOptions.SO_LINGER, newBoolean(on));

} else{

if (linger < 0) {

throw new IllegalArgumentException("invalid value for SO_LINGER");

}

if (linger > 65535)

linger = 65535;

getImpl().setOption(SocketOptions.SO_LINGER, newInteger(linger));

}

}

這個字段對Socket的close方法產(chǎn)生影響，當(dāng)這個字段設(shè)置為false時，close會立即執(zhí)行并返回，如果這時仍然有未被送出的數(shù)據(jù)包，那么這些數(shù)據(jù)包將被丟棄。如果設(shè)置為True時，有一個延遲時間可以設(shè)置。這個延遲時間就是close真正執(zhí)行所有等待的時間，最大為65535。

11、public final static int SO_TIMEOUT = 0x1006;

/*** Enable/disable SO_TIMEOUT with the specified timeout, in

* milliseconds. With this option set to a non-zero timeout,

* a read() call on the InputStream associated with this Socket

* will block for only this amount of time. If the timeout expires,

* a java.net.SocketTimeoutException is raised, though the

* Socket is still valid. The option must be enabled

* prior to entering the blocking operation to have effect. The

* timeout must be > 0.

* A timeout of zero is interpreted as an infinite timeout.

* @paramtimeout the specified timeout, in milliseconds.

* @exceptionSocketException if there is an error

* in the underlying protocol, such as a TCP error.

* @sinceJDK 1.1

* @see#getSoTimeout()

*/

public synchronized void setSoTimeout(int timeout) throwsSocketException {

if(isClosed())

throw new SocketException("Socket is closed");

if (timeout < 0)

throw new IllegalArgumentException("timeout can't be negative");

getImpl().setOption(SocketOptions.SO_TIMEOUT, newInteger(timeout));

}

這個參數(shù)用來控制客戶端讀取socket數(shù)據(jù)的超時時間，如果timeout設(shè)置為0，那么就一直阻塞，否則阻塞直到超時后直接拋超時異常。

12、public final static int SO_SNDBUF = 0x1001;

在默認情況下，輸出流的發(fā)送緩沖區(qū)是8096個字節(jié)(8K)。這個值是Java所建議的輸出緩沖區(qū)的大小。如果這個默認值不能滿足要求，可以用setSendBufferSize方法來重新設(shè)置緩沖區(qū)的大小。

13、public final static int SO_RCVBUF = 0x1002;

在默認情況下，輸入流的接收緩沖區(qū)是8096個字節(jié)(8K)。這個值是Java所建議的輸入緩沖區(qū)的大小。如果這個默認值不能滿足要求，可以用setReceiveBufferSize方法來重新設(shè)置緩沖區(qū)的大小。

14、public final static int SO_KEEPALIVE = 0x0008;

如果將這個參數(shù)這是為True，客戶端每隔一段時間(一般不少于2小時)就像服務(wù)器發(fā)送一個試探性的數(shù)據(jù)包，服務(wù)器一般會有三種回應(yīng)：

1、服務(wù)器正常回一個ACK，這表明遠程服務(wù)器一切OK，那么客戶端不會關(guān)閉連接，而是再下一個2小時后再發(fā)個試探包。

2、服務(wù)器返回一個RST，這表明遠程服務(wù)器掛了，這時候客戶端會關(guān)閉連接。

3、如果服務(wù)器未響應(yīng)這個數(shù)據(jù)包，在大約11分鐘后，客戶端Socket再發(fā)送一個數(shù)據(jù)包，如果在12分鐘內(nèi)，服務(wù)器還沒響應(yīng)，那么客戶端Socket將關(guān)閉。

15、public final static int SO_OOBINLINE = 0x1003;

如果這個Socket選項打開，可以通過Socket類的sendUrgentData方法向服務(wù)器發(fā)送一個單字節(jié)的數(shù)據(jù)。這個單字節(jié)數(shù)據(jù)并不經(jīng)過輸出緩沖區(qū)，而是立即發(fā)出。雖然在客戶端并不是使用OutputStream向服務(wù)器發(fā)送數(shù)據(jù)，但在服務(wù)端程序中這個單字節(jié)的數(shù)據(jù)是和其它的普通數(shù)據(jù)混在一起的。因此，在服務(wù)端程序中并不知道由客戶端發(fā)過來的數(shù)據(jù)是由OutputStream還是由sendUrgentData發(fā)過來的。

http://www.cnblogs.com/biakia/p/4321800.html

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