Netty源码分析之ChannelPipeline—异常事件的传播
ChannelHandler中异常的获取与处理是通过继承重写exceptionCaught方法来实现的,本篇文章我们对ChannelPipeline中exceptionCaught异常事件的传播进行梳理分析
1、出站事件的传播示例
首先我们继续在之前的代码上进行改造,模拟异常事件的传播
public class ServerApp {
public static void main(String[] args) {
EventLoopGroup boss = new NioEventLoopGroup();
EventLoopGroup work = new NioEventLoopGroup(2);
try {
ServerBootstrap bootstrap = new ServerBootstrap();
bootstrap.childOption(ChannelOption.SO_SNDBUF,2);
bootstrap.group(boss, work).channel(NioServerSocketChannel.class)
.childHandler(new ChannelInitializer<SocketChannel>() {
@Override
public void initChannel(SocketChannel ch) throws Exception {
ChannelPipeline p = ch.pipeline();
// p.addLast(new LoggingHandler(LogLevel.INFO));
// 向ChannelPipeline中添加自定义channelHandler
p.addLast(new OutHandlerA());
p.addLast(new ServerHandlerA());
p.addLast(new ServerHandlerB());
p.addLast(new ServerHandlerC());
p.addLast(new OutHandlerB());
p.addLast(new OutHandlerC()); }
});
bootstrap.bind(8050).sync(); } catch (Exception e) {
// TODO: handle exception
} } } public class OutHandlerA extends ChannelOutboundHandlerAdapter {
@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause)
throws Exception {
System.err.println(this.getClass().getName()+"---"+cause.getMessage());
ctx.fireExceptionCaught(cause);
}
} public class OutHandlerB extends ChannelOutboundHandlerAdapter {
@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause)
throws Exception {
System.err.println(this.getClass().getName()+"---"+cause.getMessage());
ctx.fireExceptionCaught(cause);
}
} public class OutHandlerC extends ChannelOutboundHandlerAdapter {
@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause)
throws Exception {
System.err.println(this.getClass().getName()+"---"+cause.getMessage());
ctx.fireExceptionCaught(cause);
}
} public class ServerHandlerB extends ChannelInboundHandlerAdapter {
@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause)
throws Exception {
System.err.println(this.getClass().getName()+"---"+cause.getMessage());
ctx.fireExceptionCaught(cause);
}
} public class ServerHandlerC extends ChannelInboundHandlerAdapter {
@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause)
throws Exception {
System.err.println(this.getClass().getName()+"---"+cause.getMessage());
ctx.fireExceptionCaught(cause);
}
}
然后我们在ServerHandlerA的channelRead方法中执行ctx的write方法,模拟异常事件的发生。
@Override
public void channelRead(ChannelHandlerContext ctx, Object object) {
ctx.fireExceptionCaught(new Throwable("出现异常"));
//ctx.pipeline().fireExceptionCaught(new Throwable("出现异常")); }
我们首先看下运行结果
ctx.fireExceptionCaught
io.netty.example.echo.my.ServerHandlerB---出现异常
io.netty.example.echo.my.ServerHandlerC---出现异常
io.netty.example.echo.my.OutHandlerB---出现异常
io.netty.example.echo.my.OutHandlerC---出现异常
18:34:17.147 [nioEventLoopGroup-3-1] WARN i.n.channel.DefaultChannelPipeline - An exceptionCaught() event was fired, and it reached at the tail of the pipeline. It usually means the last handler in the pipeline did not handle the exception.
java.lang.Throwable: 出现异常
at io.netty.example.echo.my.ServerHandlerA.channelRead(ServerHandlerA.java:39)
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:363)
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:348)
at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:338)
at io.netty.channel.DefaultChannelPipeline$HeadContext.channelRead(DefaultChannelPipeline.java:1424)
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:363)
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:348)
at io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:944)
at io.netty.channel.nio.AbstractNioByteChannel$NioByteUnsafe.read(AbstractNioByteChannel.java:163)
at io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:709)
at io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized(NioEventLoop.java:639)
at io.netty.channel.nio.NioEventLoop.processSelectedKeys(NioEventLoop.java:553)
at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:510)
at io.netty.util.concurrent.SingleThreadEventExecutor$5.run(SingleThreadEventExecutor.java:912)
at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30)
at java.lang.Thread.run(Thread.java:748)
ctx.pipeline().fireExceptionCaught
io.netty.example.echo.my.OutHandlerA---出现异常
io.netty.example.echo.my.ServerHandlerA---出现异常
io.netty.example.echo.my.ServerHandlerB---出现异常
io.netty.example.echo.my.ServerHandlerC---出现异常
io.netty.example.echo.my.OutHandlerB---出现异常
io.netty.example.echo.my.OutHandlerC---出现异常
20:08:53.723 [nioEventLoopGroup-3-1] WARN i.n.channel.DefaultChannelPipeline - An exceptionCaught() event was fired, and it reached at the tail of the pipeline. It usually means the last handler in the pipeline did not handle the exception.
java.lang.Throwable: 出现异常
at io.netty.example.echo.my.ServerHandlerA.channelRead(ServerHandlerA.java:40)
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:363)
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:348)
at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:338)
at io.netty.channel.DefaultChannelPipeline$HeadContext.channelRead(DefaultChannelPipeline.java:1424)
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:363)
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:348)
at io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:944)
at io.netty.channel.nio.AbstractNioByteChannel$NioByteUnsafe.read(AbstractNioByteChannel.java:163)
at io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:709)
at io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized(NioEventLoop.java:639)
at io.netty.channel.nio.NioEventLoop.processSelectedKeys(NioEventLoop.java:553)
at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:510)
at io.netty.util.concurrent.SingleThreadEventExecutor$5.run(SingleThreadEventExecutor.java:912)
at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30)
at java.lang.Thread.run(Thread.java:748)
根据输出结果可以看出ctx.fireExceptionCaught 会从异常产生的ChannelHandler一直往后传播到tail尾节点,ctx.pipeline().fireExceptionCaught会从管道中第一个节点一直往后传播到tail尾节点,而上面结果中打印的异常信息则是在TailContext尾节点中统一处理的。
2、异常事件传播的分析
ctx.pipeline().fireExceptionCaught与ctx.fireExceptionCaught两种传播异常方法
前者调用的是DefaultChannelPipeline 的 fireExceptionCaught方法
@Override
public final ChannelPipeline fireExceptionCaught(Throwable cause) {
AbstractChannelHandlerContext.invokeExceptionCaught(head, cause);
return this;
}
后者调用的是AbstractChannelHandlerContext 的 fireExceptionCaught方法
@Override
public ChannelHandlerContext fireExceptionCaught(final Throwable cause) {
invokeExceptionCaught(next, cause);
return this;
}
可以看到DefaultChannelPipeline的fireExceptionCaught方法中默认传入了head头部节点,所以ctx.pipeline().fireExceptionCaught会从管道中第一个节点开始向后传播。
我们进入invokeExceptionCaught方法内部看下具体实现
static void invokeExceptionCaught(final AbstractChannelHandlerContext next, final Throwable cause) {
ObjectUtil.checkNotNull(cause, "cause");//检查异常是否为空
EventExecutor executor = next.executor();
if (executor.inEventLoop()) {//判断是否与当前线程一直
next.invokeExceptionCaught(cause);//触发回调,触发下一个AbstractChannelHandlerContext节点中handler的异常处理事件
} else {
try {
executor.execute(new Runnable() {//如果线程不一致,由其绑定的executor执行
@Override
public void run() {
next.invokeExceptionCaught(cause);
}
});
} catch (Throwable t) {
if (logger.isWarnEnabled()) {
logger.warn("Failed to submit an exceptionCaught() event.", t);
logger.warn("The exceptionCaught() event that was failed to submit was:", cause);
}
}
}
invokeExceptionCaught方法内部实现
private void invokeExceptionCaught(final Throwable cause) {
if (invokeHandler()) {//判断当前handler的状态
try {
handler().exceptionCaught(this, cause);//调用exceptionCaught方法实现
} catch (Throwable error) {
if (logger.isDebugEnabled()) {
logger.debug(
"An exception {}" +
"was thrown by a user handler's exceptionCaught() " +
"method while handling the following exception:",
ThrowableUtil.stackTraceToString(error), cause);
} else if (logger.isWarnEnabled()) {
logger.warn(
"An exception '{}' [enable DEBUG level for full stacktrace] " +
"was thrown by a user handler's exceptionCaught() " +
"method while handling the following exception:", error, cause);
}
}
} else {
fireExceptionCaught(cause);
}
}
3、异常处理机制的设计
通过上面的分析我们可以看到如果通过ctx.fireExceptionCaught一直向后传递异常事件,最终会触发尾节点的exceptionCaught事件打印异常日志;
@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {
onUnhandledInboundException(cause);
}
protected void onUnhandledInboundException(Throwable cause) {
try {
logger.warn(
"An exceptionCaught() event was fired, and it reached at the tail of the pipeline. " +
"It usually means the last handler in the pipeline did not handle the exception.",
cause);
} finally {
ReferenceCountUtil.release(cause);
}
}
在实际项目中我们可以在ChannelPipeline尾部增加一个异常处理handle用来统一处理异常信息;
public void initChannel(SocketChannel ch) throws Exception {
ChannelPipeline p = ch.pipeline();
// p.addLast(new LoggingHandler(LogLevel.INFO));
// 向ChannelPipeline中添加自定义channelHandler
p.addLast(new OutHandlerA());
p.addLast(new ServerHandlerA());
p.addLast(new ServerHandlerB());
p.addLast(new ServerHandlerC());
p.addLast(new OutHandlerB());
p.addLast(new OutHandlerC());
p.addLast(new ExceptionHandler()); }
通过以上三点内容我们对异常信息在ChannelPipeline中的传播进行了模拟,梳理事件的传播流程以及应该怎样统一处理异常信息,其中如有不足与不正确的地方还望指出与海涵。
关注微信公众号,查看更多技术文章。
最新文章
- BCP
- angular源码分析:angular中各种常用函数,比较省代码的各种小技巧
- login placeholder
- struts2与cookie实现自动登录和验证码验证
- SSH应该使用密钥还是密码?
- 显示ubuntu 10.4右上角网络图标
- 拓扑排序<;反向拓扑+有向环的判断>;
- 移动端JS事件、移动端框架
- angular $compile的使用
- 客户端怎么查看SVN的代码库
- Python:bs4中 string 属性和 text 属性的区别及背后的原理
- window.open() &; iframe &; tab
- seaborn库
- [转] React Hot Loader 3 beta 升级指南
- PAT 甲级 1134 Vertex Cover
- Python的字符串内建函数(字符串处理)
- 模拟ATM的功能
- acm 2001
- Hadoop日记Day14---MapReduce源代码回顾总结
- 做业5.2 TDD