java-NIO-ServerSocketChannel
ServerSocketChannel
一. Channel接口
public interface Channel extends Closeable {
public boolean isOpen();
public void close() throws IOException;
}
二. ServerSocketChannel
总体代码如下：
ServerSocketChannel serverSocketChannel = ServerSocketChannel.open();
ServerSocket socket = serverSocketChannel.socket();
socket.bind(new InetSocketAddress(9999));
while(true){
SocketChannel socketChannel =
serverSocketChannel.accept();
//do something with socketChannel...
ServerSocketChannel的open方法如下
public static ServerSocketChannel open() throws IOException {
return SelectorProvider.provider().openServerSocketChannel();
}
三. 创建SelectorProvider，构造ServerSocketChannelImpl
public static SelectorProvider provider() {
synchronized (lock) {
if (provider != null)
return provider;
return AccessController.doPrivileged(
new PrivilegedAction<SelectorProvider>() {
public SelectorProvider run() {
if (loadProviderFromProperty())
return provider;
if (loadProviderAsService())
return provider;
provider = sun.nio.ch.DefaultSelectorProvider.create();
return provider;
}
});
}
}
doPrivileged是本地方法，把PrivilegedAction这个接口函数传进去
public interface PrivilegedAction<T> {
T run();
}
run方法，返回SelectorProvider
然后通过如下三种方式尝试获取provider
- java.nio.channels.spi.SelectorProvider
- loadProviderAsService() 加载
- sun.nio.ch.DefaultSelectorProvider.create()
但是最后成功的只有第三种方法
DefaultSelectorProvider根据平台区分，linux平台如下；
public class DefaultSelectorProvider {
private DefaultSelectorProvider() { }
//创建EPollSelectorProvider
@SuppressWarnings("unchecked")
private static SelectorProvider createProvider(String cn) {
Class<SelectorProvider> c;
try {
c = (Class<SelectorProvider>)Class.forName(cn);
} catch (ClassNotFoundException x) {
throw new AssertionError(x);
}
try {
return c.newInstance();
} catch (IllegalAccessException | InstantiationException x) {
throw new AssertionError(x);
}
}
public static SelectorProvider create() {
String osname = AccessController.doPrivileged(new GetPropertyAction("os.name"));
if (osname.equals("SunOS"))
return createProvider("sun.nio.ch.DevPollSelectorProvider");
if (osname.equals("Linux"))
return createProvider("sun.nio.ch.EPollSelectorProvider");
return new sun.nio.ch.PollSelectorProvider();
}
linux平台下利用反射创建EPollSelectorProvider
经过这个过程，把SelectorProvider这个类的provider修改为EPollSelectorProvider，并返回
继承关系如下：
EPollSelectorProvider->SelectorProviderImpl->SelectorProvider
openServerSocketChannel
openServerSocketChannel方法，把自身EPollSelectorProvider作为参数传入，并且构造一个ServerSocketChannelImpl
public ServerSocketChannel openServerSocketChannel() throws IOException {
return new ServerSocketChannelImpl(this);
}
四. ServerSocketChannel
可以看出ServerSocketChannel是ServerSocketChannelImpl，其socket方法如下
把ServerSocketChannelImpl作为参数，传入ServerSocketAdaptor，然后构造了一个ServerSocketAdaptor返回
public ServerSocket socket() {
synchronized (stateLock) {
if (socket == null)
socket = ServerSocketAdaptor.create(this);
return socket;
}
}
ServerSocketAdaptor是一个ServerSocket
内部操持了一个重要的参数
private final ServerSocketChannelImpl ssc;
ServerSocketAdaptor
继承关系如下：
ServerSocketAdaptor->ServerSocket
够造时把ServerSocketChannelImpl传入，最后调用默认的构造方法，并设置内部的ssc为ServerSocketChannelImpl
public static ServerSocket create(ServerSocketChannelImpl ssc) {
try {
return new ServerSocketAdaptor(ssc);
} catch (IOException x) {
throw new Error(x);
}
}
即bind(new InetSocketAddress(9999))调用的是ServerSocketAdaptor的bind方法
InetSocketAddress实际是SocketAddress的子类，构造过：
public InetSocketAddress(int port) {
this(InetAddress.anyLocalAddress(), port);
}
InetAddress管理ip地址的工具类
static InetAddress anyLocalAddress() {
return impl.anyLocalAddress();
}
impl的构造
InetAddress的静态初始化代码构造，最后构造出java.net.Inet4AddressImpl
impl = InetAddressImplFactory.create();
InetAddressImplFactory类在InetAddress内部，isIPv6Supported获取系统参数，判断是否ipv6模式，然后提供一个比如Inet4AddressImpl，传入loadImpl方法
class InetAddressImplFactory {
static InetAddressImpl create() {
return InetAddress.loadImpl(isIPv6Supported() ?
"Inet6AddressImpl" : "Inet4AddressImpl");
}
static native boolean isIPv6Supported();
}
利用反射构造InetAddressImpl
static InetAddressImpl loadImpl(String implName) {
Object impl = null;
//从系统获取impl.prefix的value，如果没有就为空，这里为空
String prefix = AccessController.doPrivileged(
new GetPropertyAction("impl.prefix", ""));
try {
impl = Class.forName("java.net." + prefix + implName).newInstance();
} catch (ClassNotFoundException e) {
System.err.println("Class not found: java.net." + prefix +
implName + ":\ncheck impl.prefix property " +
"in your properties file.");
} catch (InstantiationException e) {
System.err.println("Could not instantiate: java.net." + prefix +
implName + ":\ncheck impl.prefix property " +
"in your properties file.");
} catch (IllegalAccessException e) {
System.err.println("Cannot access class: java.net." + prefix +
implName + ":\ncheck impl.prefix property " +
"in your properties file.");
}
if (impl == null) {
try {
impl = Class.forName(implName).newInstance();
} catch (Exception e) {
throw new Error("System property impl.prefix incorrect");
}
}
return (InetAddressImpl) impl;
}
anyLocalAddress
我们知道构造的是java.net.Inet4AddressImpl
public synchronized InetAddress anyLocalAddress() {
if (anyLocalAddress == null) {
anyLocalAddress = new Inet4Address(); // {0x00,0x00,0x00,0x00}
anyLocalAddress.holder().hostName = "0.0.0.0";
}
return anyLocalAddress;
}
anyLocalAddresss是一个Inet4Address构造过程
Inet4Address->InetAddress
Inet4Address() {
super();
holder().hostName = null;
holder().address = 0;
holder().family = IPv4;
}
父类中构造的这个holder,设置为0.0.0.0
InetAddress() {
holder = new InetAddressHolder();
}
最后返回的是一个Inet4Address，并且hostname为0
回到InetSocketAddress创建
public InetSocketAddress(int port) {
this(InetAddress.anyLocalAddress(), port);
}
继续调用
InetSocketAddress内部也创建一个InetSocketAddressHolder
传入的addr就是构建的Inet4Address
public InetSocketAddress(InetAddress addr, int port) {
holder = new InetSocketAddressHolder(
null,
addr == null ? InetAddress.anyLocalAddress() : addr,
checkPort(port));
}
主要构建并返回一个InetSocketAddressHolder，默认的参数如下
hostname = null;
addr = Inet4Address;
port = port;
这样就构建了一个InetSocketAddress，其实都是0
五. bind方法
回顾一下
ServerSocket socket = serverSocketChannel.socket();
socket.bind(new InetSocketAddress(9999));
ServerSocketChannelImpl调用socket方法，其实是ServerSocketAdaptor调用了create方法，并把ServerSocketChannelImpl作为参数传进去
最后构建了一个ServerSocketAdaptor，然后返回，后来调用bind方法就是ServerSocketAdaptor的bind方法
socket.bind(new InetSocketAddress(9999));
把Inet4Address传入
public void bind(SocketAddress local) throws IOException {
bind(local, 50);
}
继续bind调用的ServerSocketChannelImpl的bind方法
public void bind(SocketAddress local, int backlog) throws IOException {
if (local == null)
local = new InetSocketAddress(0);
try {
ssc.bind(local, backlog);
} catch (Exception x) {
Net.translateException(x);
}
}
ServerSocketChannelImpl的bind方法如下
调用c方法，做了两个操作
- 把文件描述符，InetSocketAddress和端口号绑定到一起
- 监听这个端口号
public ServerSocketChannel bind(SocketAddress local, int backlog) throws IOException {
synchronized (lock) {
if (!isOpen())
throw new ClosedChannelException();
if (isBound())
throw new AlreadyBoundException();
InetSocketAddress isa = (local == null) ? new InetSocketAddress(0) :
Net.checkAddress(local);
SecurityManager sm = System.getSecurityManager();
if (sm != null)
sm.checkListen(isa.getPort());
//啥也没做
NetHooks.beforeTcpBind(fd, isa.getAddress(), isa.getPort());
//调用bind和listen
Net.bind(fd, isa.getAddress(), isa.getPort());
Net.listen(fd, backlog < 1 ? 50 : backlog);
synchronized (stateLock) {
localAddress = Net.localAddress(fd);
}
}
return this;
}
五. accept方法
可以看出，这里比较有趣的一个地方，用ServerSocketAdaptor去bind，用ServerSocketChannelImpl去accept
accept0(this.fd, newfd, isaa)这个操作是非阻塞的，通过返回值n控制是否阻塞SocketChannelImpl返回
1 成功
IOStatus.UNAVAILABLE 失败，非阻塞，并且没有pending
IOStatus.INTERRUPTED 失败，阻塞
如果这个连接创建好了，设置阻塞模式，默认为true，然后创建一个
public SocketChannel accept() throws IOException {
synchronized (lock) {
if (!isOpen())
throw new ClosedChannelException();
if (!isBound())
throw new NotYetBoundException();
SocketChannel sc = null;
int n = 0;
FileDescriptor newfd = new FileDescriptor();
InetSocketAddress[] isaa = new InetSocketAddress[1];
try {
begin();
if (!isOpen())
return null;
thread = NativeThread.current();
for (;;) {
//调用本地的accept方法
n = accept0(this.fd, newfd, isaa);
if ((n == IOStatus.INTERRUPTED) && isOpen())
continue;
break;
}
} finally {
thread = 0;
end(n > 0);
assert IOStatus.check(n);
}
if (n < 1)
return null;
//配置文件描述符是否阻塞
IOUtil.configureBlocking(newfd, true);
//远端连接的地址
InetSocketAddress isa = isaa[0];
//传入连接，连理一个新的SocketChannelImpl
sc = new SocketChannelImpl(provider(), newfd, isa);
SecurityManager sm = System.getSecurityManager();
if (sm != null) {
try {
sm.checkAccept(isa.getAddress().getHostAddress(),
isa.getPort());
} catch (SecurityException x) {
sc.close();
throw x;
}
}
return sc;
}
}
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