fundamental networking in java：
1.summary
用java开发网络编程应用优势在于：
1.跨平台型
2.轻量级线程模型 网络编程跟多线程结合
3.安全性 没有指针，垃圾回收机制；很好的异常处理机制，oom异常也能捕获；未捕获的运行时异常只影响所在的线程，不影响进程。
4.可扩展性灵活性，以及良好丰富的类库。java的网络库更简单易用。
2 IP：
Socket：一台机器的通讯节点称为socket，在java中，socket是java.net包里面的Socket,ServerSocket,DataGramSocket,MultiSocket的实例。
IP地址java中用java.net.InetAddress来表示。
java network address class包括：
InetAddress：ip地址或者域名，指向远程地址。如果域名解析不了，则出错。
抽象类，有两个子类：Inet4Address和Inet6Address。这两个类智能通过InetAddress的静态方法获取，不能直接构造。包可见。
InetSocketAddress extends SocketAddress：ip socket地址，用{ip，port}或者{hostname，port}表示。也能够单独用port构造，表示本机ip地址，所有本机网络地址。
NetwordInterface：本机网络接口，由多个网络接口名称和对应的网络接口的ip地址列表构成。
网络主机有两个特殊的网络地址：
loopback：127.0.0.1 用来检测本机的host名称，或者检测本地ip地址是否可用
wildcard：0.0.0.0 绑定了本机所有的ip地址
IPV6支持IPV4，可以通过以下的环境变量对ipv4和ipv6进行设置
java.net.preferlPv4Stack false(default)/true false:表示支持ipv4heipv6，true表示只支持ipv4，
java.net.preferlPv6Address false(default)/true false，如果ipv6可用，则ipv4地址会覆盖掉ipv6地址，如果为true，则ipv6会覆盖ipv4地址，通讯地址使用ipv6.
3.TCP： 可靠的，基于流的连接，双向的
两种TCP socket：active和passive（listening）
serversocket：create a socket->binds to a port -> listen() -> loop accepte client connect -> read/write
client socket:create a socket -> connect to a address -> read/write
连接：三次握手：最多重试三次，第一次3-6s，后面double。
关闭连接：四次握手
server socket：
如果port设置为0，不设置，则系统会自动分配一个端口。如果设置为1-1023端口，需要高级用户权限。
backlog：请求队列最大长度，服务器端等待请求的最大队列数。默认50.
localaddress:server监听的本机地址，默认是所有的。
setReuseAddress(boolean on)：如果停止服务之后，需要马上重启服务，那么之前的端口可能还占用导致启动不了。设置该参数表示该地址可以重用。
setReceiveBufferSize (int size)：设置接收缓冲区大小。必须在绑定端口之前设置。为了达到更大的吞吐量，可以设置得大一点（>64k）。但是跟sendBufferSize最好配合使用。
client socket：
如果port不设置，则默认跟连接的server一致。
setSendBufferSize(int size)必须在connect之前设置
Socket IO:
DataOutputStream DataInputStream ObjectInputStream ObjectOutputStream
可能导致死锁：下面两行代码顺序可能导致死锁，因为server和client的ObjectInputStream都尝试读取对方的object stream header的数据，这样导致server和client都在等待，处于死锁。获取ObjectOutputStream必须在获取ObjectInputStream之前。
ObjectInputStream in = new ObjectInputStream(socket.getInputStream());
ObjectOutputStream out = new ObjectOutputStream(socket.getOutputStream());
InputStream.available()获取当前socket buffer的大小。
channel IO：
output shutdown：半关闭
class Socket
{
void shutdownOutput() throws IOException;
boolean isOutputShutdown();
}
特点：1.可读不可写；2.当socket关闭时，会close该连接。3.另一端read时会得到EOF异常
在proxy中，copy input to output时需要close output，这样才能把代理端的EOF也复制。如果不需要read操作，可以关闭output，减少reply数据的计算和传输的资源。
Socket.close()异步操作
input shutdown：半关闭
class Socket
{
void shutdownInput() throws IOException;
boolean isInputShutdown();
}
特点：1直接丢弃数据，远程端无法感知本地已经关闭input。
close a connected socket:
class Socket
{
void close() throws IOException;
boolean isClosed();
}
1.socket.close() 2 socket.getOutputStream().close(); 3 socket.getInputStream().close();
close a server socket:
class ServerSocket
{
void close() throws IOException;
boolean isClosed();
}
socket factory:
java 提供三种socket factory：
java.net socket factory:SocketImplFactory Socket类的public static synchronized void setSocketImplFactory(SocketImplFactory fac)只能在一个jvm中调用一次，需要RuntimePermission ‘setFactory’
RMI socket factory：RMISocketFactory RMIServerSocketFactory RMIClientSocketFactory
ssl socket factory.
socket：sendbuffer和receivebuffer的大小由tcp协议栈决定，不是由jvm。传统的tcp实现默认是2kb，但是现在更多的如28kb，32kb，64kb。
1.以太网最好从4kb增大到16kb >=3 * MSS sendbuffer>=receivebuffer
2.如果应用读取数据很慢，那么receivebuffer要设置得大一点，避免阻塞sendbuffer。
3.应用程序如果要发送也要接受大量数据，则需要增加这两个值。
4.java中最好使用bufferoutputStream或者ByteBuffer，来写入足够数据的TCP块。
//立刻发送urgentdata的数据，而write的数据要flush之后才发送。server和client都要同时开启。
socket.setOOBInline(true);
socket.sendUrgentData(65);
public void setTrafficClass(int tc)
* <UL>
* <LI><CODE>IPTOS_LOWCOST (0x02)</CODE></LI>
* <LI><CODE>IPTOS_RELIABILITY (0x04)</CODE></LI>
* <LI><CODE>IPTOS_THROUGHPUT (0x08)</CODE></LI>
* <LI><CODE>IPTOS_LOWDELAY (0x10)</CODE></LI>
* </UL>
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
* <tt>(1, 0, 0)</tt>. 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 <tt>(0, 1, 2)</tt>.
public void setPerformancePreferences(int connectionTime,
int latency,
int bandwidth)
scaable IO：
channel create：
FileChannel FileInputStream.getChannel();
FileChannel FileOutputStream.getChannel();
FileChannel RandomAccessFile.getChannel();
SocketChannel channel = SocketChannel.open();
Socket socket = channel.socket();
ServerSocketChannel channel = ServerSocketChannel.open();
ServerSocket serverSocket = channel.socket();
DatagramChannel channel = DatagramChannel.open();
DatagramSocket datagramSocket = channel.socket();
//
Pipe pipe = Pipe.open();
Pipe.SinkChannel sinkChannel = pipe.sink();
Pipe.SourceChannel sourceChannel = pipe.source();
Stream和channel的转换：Channels.java
//not buffered,not support mart/reset operation;thread safe;only be use in blocking mode;closing them cause the underlying channel to be closed;
class Channels
{
// convert streams to channels
static ReadableByteChannel newChannel(InputStream is);
static WritableByteChannel newChannel(OutputStream os);
// convert channels to streams
static InputStream
newInputStream(ReadableByteChannel ch);
static OutputStream
newOutputStream(WritableByteChannel ch);
}
selector的select方法：如果返回0，则可能超时selector被异步唤醒；a register key被异步取消。
selectkey set只有在调用select(),select(long timeout)才被更新，处理完之后需要显示remove掉已经处理过得selectkey。
selector.wakeup() will cause的next first block return immediately。wakeup()：set a boolean status
blocking TCP connect():connect() ilock
noblocking TCP connect():cnnect() return true immediately，finishConnect() to check connect is ok.isConnectionPending() and finishConnect() only user in noblocking mode.
socketChannel.close();1.cannel the selectkey associated with the channel;2 channel.close();must invoke selector.selectNow();
1.only use OP_CONNECT on unconnect socket;it must be removed from keys as soon as channel is ready;2.only use OP_WRITE on connect socket;
firewalls:1.transport firewalls;2application firewalls.
HTTP proxy server:java 能够通过设置环境变量http.proxyHost和http.proxyPort通过代理服务器发送http请求。to get http tunnelling in rmi or httpConnect.
Socket proxy：socksProxyHost and socksProxyPort to user a socket proxy
java.net.Proxy:
secure socket
handShake protocal:
SSlSocket:1.firest create take more time;2use bufferOutputStream;3 not support OOBinline;4.SSlSocket.getInputStream().available() always return 0.
5.serveer/client must close at the same time,not support shutdownInput or shutDownoutput
(a) To view all debugging messages:
-Djavax.net.debug=all
(b) To view the hexadecimal dumps of each handshake message:
-Djavax.net.debug=ssl:handshake:data
(c) To view the hexadecimal dumps of each handshake message, an
trust manager tracing (the commas are optional):
-Djavax.net.debug=SSL:handshake:data:trustmanager
SSL system properties:
https.cipherSuites
https.protocals
https.proxyHost
https.proxyPort
java.net.protocal.handler.pkgs
javax.net.debug
javax.net.ssl.keyStore
javax.net.ssl.keyStorePassword
javax.net.ssl.keyStoreType
javax.net.trustStore
javax.net.trustStorePassword
javax.net.trustStoreType
scalable secure socket:
javax.net.ssl.Sslengine
unicast UDP:
ipv4 65507byte
udp:512byte a ip package size
udp:没有建立连接和关闭连接的开销；服务器和客户端管理简单；
a:trasaction is request-reply;b:payloads is small;c:servers are stateless;d:Trasactions can be repeated;
receive, send is synchronized
reliable UDP:(DNS)
1.sequence number; 2 timeout and retransmits
ACK and NACK based protocol
scalable UDP:
muliticast UDP:
1. multicast address a dynamic group address
resuce the load;receive the package almost at the same time;fesable;
reliable;co-operation from routers;security;
2. broadcast a static group address
3. IPV6 anycast only receive by any one of the group members
TTL based Scopes
Address based Scopes
Tree-based protocals
NACK-based protocals
ACL
Reactor,Proactor,leader-follower server