一、简介
引导一个应用程序是指对它进行配置,并使它运行起来的过程。
服务器致力于使用一个父
Channel
来接受来自客户端的连接,并创建子Channel
用于它们之间的通信
可分为:Bootstrap
和 ServerBootstrap
关于IllegalStateException
,在调用bind()
或者 connect()
方法之前,必须调用:
group()
channel()
或者channelFactory()
handler()
(1)Bootstrap
Bootstrap
类负责为客户端和使用无连接协议的应用程序创建Channel
如图:
public class BootstrapClient {
public static void main(String[] args) {
EventLoopGroup group = new NioEventLoopGroup();
// 创建一个Bootstrap类的实例以创建和连接新的客户端Channel
Bootstrap bootstrap = new Bootstrap();
// 设置EventLoopGroup,提供用于处理Channel事件的EventLoop
bootstrap.group(group)
.channel(NioSocketChannel.class)
.handler(new SimpleChannelInboundHandler<ByteBuf>() {
@Override
protected void channelRead0(ChannelHandlerContext ctx, ByteBuf msg) throws Exception {
System.out.println("Received data");
}
});
ChannelFuture future = bootstrap.connect(new InetSocketAddress("www.maning.com", 80));
future.addListener(new ChannelFutureListener() {
@Override
public void operationComplete(ChannelFuture future) throws Exception {
if (future.isSuccess()) {
System.out.println("Connection established");
} else {
System.err.println("Connection attempt failed");
future.cause().printStackTrace();
}
}
});
}
}
(2)ServerBootstrap
服务器引导过程,如图:
public class ServerBootstrapClient {
public static void main(String[] args) {
NioEventLoopGroup group = new NioEventLoopGroup();
ServerBootstrap bootstrap = new ServerBootstrap();
bootstrap.group(group)
.channel(NioServerSocketChannel.class)
.childHandler(new SimpleChannelInboundHandler<ByteBuf>() {
@Override
protected void channelRead0(ChannelHandlerContext ctx, ByteBuf msg) throws Exception {
System.out.println("Received data");
}
});
ChannelFuture future = bootstrap.bind(new InetSocketAddress(8080));
future.addListener(new ChannelFutureListener() {
@Override
public void operationComplete(ChannelFuture future) throws Exception {
if (future.isSuccess()) {
System.out.println("Server bound");
} else {
System.out.println("Bound attempt failed");
future.cause().printStackTrace();
}
}
});
}
}
二、源码分析
配置阶段的工作,主要是初始化启动类和设置相关参数。
AbstractBootstrap:
属性
// 线程组,在ServerBootstrap,为 ServerSocketChannel 服务
volatile EventLoopGroup group;
// 用去获取 Channel 的工厂
private volatile ChannelFactory<? extends C> channelFactory;
// 绑定的地址
private volatile SocketAddress localAddress;
// channel 可设置的选项
private final Map<ChannelOption<?>, Object> options = new LinkedHashMap<ChannelOption<?>, Object>();
// channel 属性,便于保存用户自定义数据
private final Map<AttributeKey<?>, Object> attrs = new LinkedHashMap<AttributeKey<?>, Object>();
// 处理器
private volatile ChannelHandler handler;
方法
group() 设置线程组
channelFactory()及channel() 设置channel工厂和channel类型
localAddress() 设置地址
option() 添加channel选项
attr() 添加属性
handler() 设置channelHander
register() 内部调用 initAndRegister() 用来初始化channel并注册到线程组
bind() 首先会调用 initAndRegister(),之后绑定IP地址,使用 Promise 保证先initAndRegister()在bind()
initAndRegister(),主要是创建netty的channel,设置options和attrs,注册到线程组
init() 抽象方法,需要子类实现
(1)初始化 init
ServerBootstrap 类图:
主要作用:创建和初始化
- 使用
SelectorProvider
打开通道 - 为
Channel
分配全局唯一的channelID
- 创建
NioMessageUnsafe
,用于netty
底层的读写操作 - 创建
ChannelPipeline
,默认是DefaultChannelPipeline
// AbstractBootstrap.java
final ChannelFuture initAndRegister() {
Channel channel = null;
try {
// 创建 netty channel
channel = channelFactory.newChannel();
// 初始化
init(channel);
} catch (Throwable t) {
if (channel != null) {
channel.unsafe().closeForcibly();
}
return new DefaultChannelPromise(channel, GlobalEventExecutor.INSTANCE).setFailure(t);
}
// 注册
ChannelFuture regFuture = config().group().register(channel);
// 是否有异常原因
if (regFuture.cause() != null) {
if (channel.isRegistered()) {
channel.close();
} else {
channel.unsafe().closeForcibly();
}
}
return regFuture;
}
- 创建
channel
channel(NioServerSocketChannel.class)
根据设置的 channel 类型,进行创建。
因为使用 class 的方法,会使用 ReflectiveChannelFactory 作为工厂类
然后调用 class 的 newInstance 方法
public B channel(Class<? extends C> channelClass) {
if (channelClass == null) {
throw new NullPointerException("channelClass");
}
return channelFactory(new ReflectiveChannelFactory<C>(channelClass));
}
// ReflectiveChannelFactory.java
@Override
public T newChannel() {
try {
return clazz.newInstance();
} catch (Throwable t) {
throw new ChannelException("Unable to create Channel from class " + clazz, t);
}
}
// NioServerSocketChannel.java
public NioServerSocketChannel() {
this(newSocket(DEFAULT_SELECTOR_PROVIDER));
}
// NioServerSocketChannel.java
private static ServerSocketChannel newSocket(SelectorProvider provider) {
try {
// 打开服务器套接字通道
// 具体的实现类有 SelectorProviderImpl EpollSelectorProvider PollSelectorProvider
// 选择器的主要工作是根据操作系统类型和版本选择合适的 Provider
// 如果 Linux 内核版本 >= 2.6,则为 EpollSelectorProvider
return provider.openServerSocketChannel();
} catch (IOException e) {
throw new ChannelException(
"Failed to open a server socket.", e);
}
}
// ServerSocketChannelImpl.java
ServerSocketChannelImpl(SelectorProvider sp) throws IOException {
super(sp);
this.fd = Net.serverSocket(true); // 文件描述符
this.fdVal = IOUtil.fdVal(fd); // 文件描述符 ID
this.state = ST_INUSE;
}
- 创建
ServerSocketChannel
时候,会先初始化父类AbstractNioMessageChannel
会创建
NioMessageUnsafe
实例,该类为Channel
提供了用于完成网络通讯相关的底层操作
如:connect()
,read()
,register()
,bind()
,close()
等
- 为
Channel
创建DefaultChannelPipeline
,初始化双向链表
在
AbstractChannel
中创建:
channelId
,全局唯一unsafe
, Netty底层封装的网络I/O操作pipeline
,DefaultChannelPipeline
protected DefaultChannelPipeline(Channel channel) {
this.channel = ObjectUtil.checkNotNull(channel, "channel");
succeededFuture = new SucceededChannelFuture(channel, null);
voidPromise = new VoidChannelPromise(channel, true);
tail = new TailContext(this);
head = new HeadContext(this);
head.next = tail;
tail.prev = head;
}
-
将
java-channel
设置为非阻塞,将关注的操作设置为SelectionKey.OP_ACCEPT
(服务器) -
调用子类
init()
完善配置,如ServerBootstrap
的init()
将启动器设置的选项和属性设置到 Netty 的 Channel 上面
向Pipeline
添加初始化Handler
,供注册后使用
void init(Channel channel) throws Exception {
final Map<ChannelOption<?>, Object> options = options0();
synchronized (options) {
setChannelOptions(channel, options, logger);
}
final Map<AttributeKey<?>, Object> attrs = attrs0();
synchronized (attrs) {
for (Entry<AttributeKey<?>, Object> e: attrs.entrySet()) {
@SuppressWarnings("unchecked")
AttributeKey<Object> key = (AttributeKey<Object>) e.getKey();
channel.attr(key).set(e.getValue());
}
}
ChannelPipeline p = channel.pipeline();
final EventLoopGroup currentChildGroup = childGroup;
final ChannelHandler currentChildHandler = childHandler;
final Entry<ChannelOption<?>, Object>[] currentChildOptions;
final Entry<AttributeKey<?>, Object>[] currentChildAttrs;
synchronized (childOptions) {
currentChildOptions = childOptions.entrySet().toArray(newOptionArray(childOptions.size()));
}
synchronized (childAttrs) {
currentChildAttrs = childAttrs.entrySet().toArray(newAttrArray(childAttrs.size()));
}
// init 初始化 添加 ChannelInitializer
p.addLast(new ChannelInitializer<Channel>() {
@Override
public void initChannel(final Channel ch) throws Exception {
final ChannelPipeline pipeline = ch.pipeline();
ChannelHandler handler = config.handler(); // 获取 config时 设置 handler
if (handler != null) {
pipeline.addLast(handler); // 将其添加到链表末尾
}
// 加入一个 ServerBootstrapAcceptor处理器,用于处理 Accept
ch.eventLoop().execute(new Runnable() {
@Override
public void run() {
pipeline.addLast(new ServerBootstrapAcceptor(
ch, currentChildGroup, currentChildHandler, currentChildOptions, currentChildAttrs));
}
});
}
});
}
(2)注册 register
这个阶段主要:将 netty channel
注册到 selector
上:
- 将
channel
注册到线程池组的selector
上 - 触发
pipeline
上面channelHandler
的channelRegistered
// AbstractBootstrap.java initAndRegister()
ChannelFuture regFuture = config().group().register(channel);
register(channel)
-> SingleThreadEventLoop.java
-> unsafe.java
的register()
// SingleThreadEventLoop.java
public ChannelFuture register(Channel channel) {
return register(new DefaultChannelPromise(channel, this));
}
// SingleThreadEventLoop.java
@Override
public ChannelFuture register(final ChannelPromise promise) {
ObjectUtil.checkNotNull(promise, "promise");
promise.channel().unsafe().register(this, promise);
return promise;
}
// AbstractChannel.java
@Override
public final void register(EventLoop eventLoop, final ChannelPromise promise) {
if (eventLoop == null) {
throw new NullPointerException("eventLoop");
}
if (isRegistered()) {
promise.setFailure(new IllegalStateException("registered to an event loop already"));
return;
}
if (!isCompatible(eventLoop)) {
promise.setFailure(
new IllegalStateException("incompatible event loop type: " + eventLoop.getClass().getName()));
return;
}
AbstractChannel.this.eventLoop = eventLoop;
if (eventLoop.inEventLoop()) {
register0(promise);
} else {
try {
eventLoop.execute(new Runnable() {
@Override
public void run() {
register0(promise);
}
});
} catch (Throwable t) {
logger.warn(
"Force-closing a channel whose registration task was not accepted by an event loop: {}",
AbstractChannel.this, t);
closeForcibly();
closeFuture.setClosed();
safeSetFailure(promise, t);
}
}
}
主要方法:register0()
private void register0(ChannelPromise promise) {
try {
// 确保通道打开
if (!promise.setUncancellable() || !ensureOpen(promise)) {
return;
}
// 是否为首次注册
boolean firstRegistration = neverRegistered;
// 注册
doRegister();
neverRegistered = false;
registered = true;
// 将注册之前加入的 handler 加入进来
pipeline.invokeHandlerAddedIfNeeded();
// 注册成功
safeSetSuccess(promise);
// pipeline通知注册成功
pipeline.fireChannelRegistered();
// 是否已经绑定,因为 register 和 bind 阶段是异步的
if (isActive()) {
if (firstRegistration) {
// 首次注册,通知
pipeline.fireChannelActive();
} else if (config().isAutoRead()) { // channel会deregister后重新注册到线程组时,且配置了AutoRead
beginRead();
}
}
} catch (Throwable t) {
closeForcibly();
closeFuture.setClosed();
safeSetFailure(promise, t);
}
}
(3)绑定 bind
此阶段,主要将 Netty Channel
中 ServerSocketChannel
绑定本地端口
结束后使用 fireChannelActive
通知 Pipeline
里的ChannelHandle
,执行其channelActive
方法
// AbstractBootstrap.java
public final void bind(final SocketAddress localAddress, final ChannelPromise promise) {
boolean wasActive = isActive();
try {
doBind(localAddress);
} catch (Throwable t) {
safeSetFailure(promise, t);
closeIfClosed();
return;
}
if (!wasActive && isActive()) {
invokeLater(new Runnable() {
@Override
public void run() {
pipeline.fireChannelActive();
}
});
}
safeSetSuccess(promise);
}