前言：对于微服务来说，如果我们要实现一个web服务，
大部分人可能直接用springboot的spring-boot-starter-web了。
我们知道spring-boot-starter-web默认实现是tomcat，当然你也可以选择其他服务器类型，比如Jetty、Undertow等。
但是如果是一个非springboot项目，该如何实现呢？
这里介绍了下四种实现方式，基于Tomcat、Jetty、JdkHttp、Netty实现内嵌web容器。
Tomcat
依赖的maven坐标：
javax.annotation
javax.annotation-api
org.apache.tomcat.embed
tomcat-embed-core
tomcat-annotations-api
org.apache.tomcat
首先看下初始化启动的代码：
Tomcat tomcatServer = new Tomcat();
//静默方式启动
tomcatServer.setSilent(true);
tomcatServer.setPort(8080);
//是否设置自动部署
tomcatServer.getHost().setAutoDeploy(false);
//创建上下文,拿到上下文后就可以设置整个访问地址了
StandardContext standardContext = new StandardContext();
standardContext.setPath(CONTEX_PATH);
//监听上下文
standardContext.addLifecycleListener(new Tomcat.FixContextListener());
// tomcat容器添加standardContext 添加整个context
tomcatServer.getHost().addChild(standardContext);
// 创建servlet servlet的名字叫IndexServlet
tomcatServer.addServlet(CONTEX_PATH, SERVLET_NAME, new JdkSimpleDispatchServlet());
// 添加servleturl映射
standardContext.addServletMappingDecoded("/*", SERVLET_NAME);
try {
tomcatServer.start();
server = tomcatServer;
} catch (Exception e) {
}上面tomcat在注册servlet的时候，自定义了一个Servlet，然后映射了/*的请求。可以查看下JdkSimpleDispatchServlet这个类，代码如下：
@Slf4j
public class JdkSimpleDispatchServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doPost(req, resp);
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
log.info("path:{}, clientIp:{}", req.getRequestURL(), req.getRemoteHost());
PrintWriter writer = resp.getWriter();
writer.print("this is index");
writer.close();
}
}Jetty
Jetty和tomcat非常类似，也是调用start方法启动。
maven依赖如下：
org.eclipse.jetty
jetty-server
org.eclipse.jetty
jetty-servlet
jetty服务初始化代码更简单，如下:
Server server = new Server(NetworkUtil.getHealthServerPort());
// ServletHandler是一种简单的创建上下文处理程序的简单方法，该上下文处理程序由Servlet实例支持。然后，需要将该处理程序注册到Server对象。
ServletHandler handler = new ServletHandler();
server.setHandler(handler);
// 这是原始Servlet，而不是已配置的Servlet，JdkSimpleDispatchServlet和tomcat的类似
handler.addServletWithMapping(JdkSimpleDispatchServlet.class, "/*");
try {
// Start things up!
server.start();
jetty = server;
} catch (Exception e) {
}
Netty
说了Tomcat和Jetty，我们再看下Netty，之前所在的一家公司就是基于Netty封装了Web服务，Netty对Web支持也比较完善，默认基于NIO的多路复用IO模型支持单机上万的吞肚量。
看下pom依赖：
io.netty
netty-all
启动方式：
public class NettyHttpServerHealthCheckServer implements IHealthCheckServer {
private static ExecutorService Pool = Executors.newSingleThreadExecutor(
new NamedThreadFactory("Netty-HealthCheck-Pool", true));
ServerBootstrap bootstrap = new ServerBootstrap();
// boss线程，只需一个
EventLoopGroup boss = new NioEventLoopGroup();
// work线程
EventLoopGroup work = new NioEventLoopGroup();
@Override
public void start() {
try {
// 因为监听服务是阻塞的，需要线程池异步监听
Pool.execute(() -> {
try {
// 配置channel、handle
bootstrap.group(boss, work)
// .handler(new LoggingHandler(LogLevel.INFO))
.channel(NioServerSocketChannel.class)
// HttpServerInitializer即http编码解码和处理配置器
.childHandler(new HttpServerInitializer());
ChannelFuture f = bootstrap.bind(new InetSocketAddress(NetworkUtil.getHealthServerPort())).sync();
// 阻塞监听
f.channel().closeFuture().sync();
} catch (Exception e) {
}
});
} catch (Exception e) {
return;
}
}
@Override
public void stop() {
boss.shutdownGracefully();
work.shutdownGracefully();
}
class HttpServerInitializer extends ChannelInitializer {
@Override
protected void initChannel(SocketChannel channel) throws Exception {
ChannelPipeline pipeline = channel.pipeline();
pipeline.addLast(new HttpServerCodec());// http 编解码
pipeline.addLast("httpAggregator", new HttpObjectAggregator(512 * 1024)); // http 消息聚合器 512*1024为接收的最大contentlength
pipeline.addLast(new HttpRequestHandler());// 请求处理器
}
}
class HttpRequestHandler extends SimpleChannelInboundHandler {
@Override
public void channelReadComplete(ChannelHandlerContext ctx) {
ctx.flush();
}
@Override
protected void channelRead0(ChannelHandlerContext ctx, FullHttpRequest req) throws Exception {
/**
* 100 Continue
* 是这样的一种情况：HTTP客户端程序有一个实体的主体部分要发送给服务器，但希望在发送之前查看下服务器是否会
* 接受这个实体，所以在发送实体之前先发送了一个携带100
* Continue的Expect请求首部的请求。服务器在收到这样的请求后，应该用 100 Continue或一条错误码来进行响应。
*/
if (is100ContinueExpected(req)) {
ctx.write(new DefaultFullHttpResponse(
HttpVersion.HTTP_1_1,
HttpResponseStatus.CONTINUE));
}
// 获取请求的uri
String path = req.uri();
// 响应请求
fireResponse(ctx, HttpResponseStatus.OK,
"hello", "text/html; charset=utf-8");
}
private void fireResponse(ChannelHandlerContext ctx, HttpResponseStatus httpResponseStatus, String resp, String contentType) {
FullHttpResponse responseDown = new DefaultFullHttpResponse(
HttpVersion.HTTP_1_1,
httpResponseStatus,
Unpooled.copiedBuffer(resp, Charset.defaultCharset()));
responseDown.headers().set(HttpHeaderNames.CONTENT_TYPE, contentType);
ctx.writeAndFlush(responseDown).addListener(ChannelFutureListener.CLOSE);
}
}
} 从上面代码可以得知，Netty默认就提供了http编解码和协议的实现，非常方便。
JdkHttp
最好介绍下不依赖第三方实现，使用JDK8内置的Http Server实现。
HttpServer类
核心类HttpServer，HttpServer是属于rt包的类，需要下载rt包的源码，配置到IDEA。或者直接使用openjdk，也可以查看到源码。
rt包可以下载OpenJDK的源码，https://download.java.net/openjdk/jdk8/promoted/b132/openjdk-8-src-b132-03_mar_2014.zip
HttpServer源码：
package com.sun.net.httpserver;
@Exported
public abstract class HttpServer {
protected HttpServer() {
}
public static HttpServer create() throws IOException {
return create((InetSocketAddress)null, 0);
}
public static HttpServer create(InetSocketAddress var0, int var1) throws IOException {
HttpServerProvider var2 = HttpServerProvider.provider();
return var2.createHttpServer(var0, var1);
}
public abstract void bind(InetSocketAddress var1, int var2) throws IOException;
public abstract void start();
public abstract void setExecutor(Executor var1);
public abstract Executor getExecutor();
public abstract void stop(int var1);
public abstract HttpContext createContext(String var1, HttpHandler var2);
public abstract HttpContext createContext(String var1);
public abstract void removeContext(String var1) throws IllegalArgumentException;
public abstract void removeContext(HttpContext var1);
public abstract InetSocketAddress getAddress();
}初始化Http服务：
public class JDKHttpServerHealthCheckServer implements IHealthCheckServer {
HttpServer server;
@Override
public void start() {
try {
// 初始化监听
server = HttpServer.create(new InetSocketAddress(8080), 100);
// 注册http请求处理类
server.createContext("/", new JdkHttpHandler());
// 启动服务
server.start();
} catch (Exception e) {
return;
}
}
@Override
public void stop() {
if (server != null) {
server.stop(0);
}
}
static class JdkHttpHandler implements HttpHandler {
@Override
public void handle(HttpExchange httpExchange) throws IOException {
String path = httpExchange.getRequestURI() == null ? "/" : httpExchange.getRequestURI().getPath();
try {
CharArrayWriter charArrayWriter = new CharArrayWriter();
charArrayWriter.write("hello");
httpExchange.getResponseHeaders().add("Content-Type", "text/plain; charset=utf-8");
// 这里必须指定字节大小，因为默认是固定大小的编码解码实现
httpExchange.sendResponseHeaders(200, charArrayWriter.size());
outputStream.write(charArrayWriter.toString().getBytes());
} catch (Exception e) {
httpExchange.sendResponseHeaders(500, 0);
}
}
}
}从上面四个实现来看，对http servlet规范支持比较完善的有Jetty、Tomcat。性能高的是Netty，实现最简单的是JDK默认HttpServer。
本文由猿必过 YBG 发布