java networking-白红宇

java networking

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发布时间：2019-06-20

本文共 7926 字，大约阅读时间需要 26 分钟。

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/writeclient 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>=receivebuffer2.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)    * 
    
          * 
     IPTOS_LOWCOST (0x02)
     * 
     IPTOS_RELIABILITY (0x04)
     * 
     IPTOS_THROUGHPUT (0x08)
     * 
     IPTOS_LOWDELAY (0x10)
     * 
    
       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). 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 channelsstatic ReadableByteChannel newChannel(InputStream is);static WritableByteChannel newChannel(OutputStream os);// convert channels to streamsstatic InputStreamnewInputStream(ReadableByteChannel ch);static OutputStreamnewOutputStream(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 statusblocking TCP connect():connect() ilocknoblocking 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 sockethandShake 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, antrust manager tracing (the commas are optional):-Djavax.net.debug=SSL:handshake:data:trustmanagerSSL system properties:https.cipherSuiteshttps.protocalshttps.proxyHosthttps.proxyPortjava.net.protocal.handler.pkgsjavax.net.debugjavax.net.ssl.keyStorejavax.net.ssl.keyStorePasswordjavax.net.ssl.keyStoreTypejavax.net.trustStorejavax.net.trustStorePasswordjavax.net.trustStoreTypescalable secure socket:javax.net.ssl.Sslengineunicast UDP:ipv4 65507byteudp:512byte a ip package sizeudp: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 synchronizedreliable UDP:(DNS)  1.sequence number; 2 timeout and retransmitsACK and NACK based protocolscalable 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 address3. IPV6 anycast only receive by any one of the group membersTTL based ScopesAddress based ScopesTree-based protocalsNACK-based protocalsACLReactor,Proactor,leader-follower server