前言

目的：

网络编程在编程领域随处可见，本文尝试手写一个简单的HttpServer，了解网络请求后台的大致思路及为学习Tomcat打好基础。

准备知识：

OOP：面向对象编程思想

collection：Java常用容器

IO：网络IO操作

Thread：多线程

Socket:网络编程

XML：配置文件解析

reflect：框架基石反射

HTML：HTML基本语法

HTTP：网络传输协议

思路

先说下大致流程：

服务端开启一个服务，进入一个死循环来给前端提供服务。

客户端发送一个HTTP请求。

服务器端收到请求后，加载一次XML文件解析，主要目的是获得客户的请求网址对应的那个Servlet(服务器端小程序)。

找到对应的Servlet后通过反射映射出实例，然后业务处理。

最终Socket通信返回结果。

流程图：

代码结构

代码实现

1. XML解析

XML文件解析的方式有多种，本文以SAXException来解析。

xml文件信息

<?xml version="1.0" encoding="UTF-8"?>  <web-app><servlet><servlet-name>login</servlet-name><servlet-class>com.sowhat.user.LoginServlet</servlet-class></servlet>   <servlet-mapping><servlet-name>login</servlet-name><url-pattern>/login</url-pattern> </servlet-mapping><servlet><servlet-name>reg</servlet-name><servlet-class>com.sowhat.user.RegisterServlet</servlet-class></servlet>   <servlet-mapping><servlet-name>reg</servlet-name><url-pattern>/r</url-pattern> </servlet-mapping></web-app>

Servlet类

xml文件中servlet体对应的Java类

package com.sowhat.server.core;
/*** 功能：servlet 映射<servlet><servlet-name>login</servlet-name><servlet-class>com.sowhat.user.LoginServlet</servlet-class></servlet>*/
public class Entity {private String name;private String clz;public Entity() {// TODO Auto-generated constructor stub}public String getName() {return name;}public void setName(String name) {this.name = name;}public String getClz() {return clz;}public void setClz(String clz) {this.clz = clz;}
}

Servlet-mapping类

servlet-mapping对应的Java类

package com.sowhat.server.core;import java.util.HashSet;
import java.util.Set;
/*** 功能： 请求网址对应的 servlet<servlet-mapping><servlet-name>login</servlet-name><url-pattern>/login</url-pattern> <url-pattern>/g</url-pattern> </servlet-mapping>**/
public class Mapping {private String name;private Set<String> patterns ;public Mapping() {patterns = new HashSet<String>();}public String getName() {return name;}public void setName(String name) {this.name = name;}public Set<String> getPatterns() {return patterns;}public void setPatterns(Set<String> patterns) {this.patterns = patterns;}public void addPattern(String pattern) {this.patterns.add(pattern);}
}

WebHandler

解析xml文件代码：WebHandler

package com.sowhat.server.core;import org.xml.sax.Attributes;
import org.xml.sax.SAXException;
import org.xml.sax.helpers.DefaultHandler;import java.util.ArrayList;
import java.util.List;/***  解析XML文件的 处理器*/
public class WebHandler extends DefaultHandler {private List<Entity> entitys = new ArrayList<Entity>();private List<Mapping> mappings = new ArrayList<Mapping>();private Entity entity;private Mapping mapping;private String tag; //存储操作标签private boolean isMapping = false;@Overridepublic void startElement(String uri, String localName, String qName, Attributes attributes) throws SAXException {if (null != qName) {tag = qName; //存储标签名if (tag.equals("servlet")) {entity = new Entity();isMapping = false;} else if (tag.equals("servlet-mapping")) {mapping = new Mapping();isMapping = true;}}}@Overridepublic void characters(char[] ch, int start, int length) throws SAXException {String contents = new String(ch, start, length).trim();if (null != tag) { //处理了空if (isMapping) { //操作servlet-mappingif (tag.equals("servlet-name")) {mapping.setName(contents);} else if (tag.equals("url-pattern")) {mapping.addPattern(contents);}} else { //操作servletif (tag.equals("servlet-name")) {entity.setName(contents);} else if (tag.equals("servlet-class")) {entity.setClz(contents);}}}}@Overridepublic void endElement(String uri, String localName, String qName) throws SAXException {if (null != qName) {if (qName.equals("servlet")) {entitys.add(entity);} else if (qName.equals("servlet-mapping")) {mappings.add(mapping);}}tag = null; //tag丢弃了}public List<Entity> getEntitys() {return entitys;}public List<Mapping> getMappings() {return mappings;}
}

WebContext

对解析结果优化映射服务：WebContext

package com.sowhat.server.core;import java.util.HashMap;
import java.util.List;
import java.util.Map;/**** 功能： 解析XML结果 HTTP网页请求跟 对应Java代码中哪个类来处理* 目的： 对XML解析后，以后输入一个请求的网址 就可以返回对应的处理类*/public class WebContext {private List<Entity> entitys = null;private List<Mapping> mappings = null;//key-->servlet-name  value -->servlet-classprivate Map<String, String> entityMap = new HashMap<String, String>();//key -->url-pattern value -->servlet-nameprivate Map<String, String> mappingMap = new HashMap<String, String>();public WebContext(List<Entity> entitys, List<Mapping> mappings) {this.entitys = entitys;this.mappings = mappings;//将entity 的List转成了对应mapfor (Entity entity : entitys) {entityMap.put(entity.getName(), entity.getClz());}//将map 的List转成了对应mapfor (Mapping mapping : mappings) {for (String pattern : mapping.getPatterns()) {mappingMap.put(pattern, mapping.getName());}}}/*** 通过URL的路径找到了对应class*/public String getClz(String pattern) {String name = mappingMap.get(pattern);return entityMap.get(name);}
}

WebApp

package com.sowhat.server.core;import javax.xml.parsers.SAXParser;
import javax.xml.parsers.SAXParserFactory;/*** 统筹 WebContext 跟 WebHandler* */public class WebApp {private static WebContext webContext;static {try {//SAX解析//1、获取解析工厂SAXParserFactory factory = SAXParserFactory.newInstance();//2、从解析工厂获取解析器SAXParser parse = factory.newSAXParser();//3、编写处理器//4、加载文档 Document 注册处理器WebHandler handler = new WebHandler();//5、解析parse.parse(Thread.currentThread().getContextClassLoader().getResourceAsStream("web.xml"), handler);//获取数据webContext = new WebContext(handler.getEntitys(), handler.getMappings());} catch (Exception e) {System.out.println("解析配置文件错误");}}/*** 通过url获取配置文件对应的servlet* @param url* @return*/public static Servlet getServletFromUrl(String url) {//假设你输入了 /loginString className = webContext.getClz("/" + url);Class clz;try {clz = Class.forName(className);Servlet servlet = (Servlet) clz.getConstructor().newInstance();return servlet;} catch (Exception e) {}return null;}
}

2. Request Response

Request 解析

package com.sowhat.server.core;import org.apache.commons.io.IOUtils;import java.io.IOException;
import java.io.InputStream;
import java.io.UnsupportedEncodingException;
import java.net.Socket;
import java.util.*;/*** 封装请求协议: 封装请求参数为Map*/
public class Request {//协议信息private String requestInfo;//请求方式private String method;//请求urlprivate String url;//请求参数private String queryStr;//存储参数private Map<String, List<String>> parameterMap;private final String CRLF = "\r\n";public Request(Socket client) throws IOException {this(client.getInputStream());System.out.println("request 构造函数");}public Request(InputStream is) {parameterMap = new HashMap<String, List<String>>();byte[] datas = new byte[1024*1024];int len;try {len = is.read(datas);this.requestInfo = new String(datas,0,len);} catch (IOException e) {e.printStackTrace();return;}//分解字符串parseRequestInfo();}//分解字符串private void parseRequestInfo() {this.method = this.requestInfo.substring(0, this.requestInfo.indexOf("/")).toLowerCase();this.method = this.method.trim();//1)、获取/的位置int startIdx = this.requestInfo.indexOf("/") + 1;//2)、获取 HTTP/的位置int endIdx = this.requestInfo.indexOf("HTTP/");//3)、分割字符串this.url = this.requestInfo.substring(startIdx, endIdx).trim();//4)、获取？的位置int queryIdx = this.url.indexOf("?");if (queryIdx >= 0) {//表示存在请求参数String[] urlArray = this.url.split("\\?");this.url = urlArray[0];queryStr = urlArray[1];}System.out.println(this.url);if (method.equals("post")) {String qStr = this.requestInfo.substring(this.requestInfo.lastIndexOf(CRLF)).trim();System.out.println(qStr + "-->");if (null == queryStr) {queryStr = qStr;} else {queryStr += "&" + qStr;}}queryStr = null == queryStr ? "" : queryStr;System.out.println(method + "-->" + url + "-->" + queryStr);//转成Map fav=1&fav=2&uname=sowhat&age=18&others=convertMap();}//处理请求参数为Mapprivate void convertMap() {//1、分割字符串 &String[] keyValues = this.queryStr.split("&");for (String queryStr : keyValues) {//2、再次分割字符串  =String[] kv = queryStr.split("=");kv = Arrays.copyOf(kv, 2);//获取key和valueString key = kv[0];String value = kv[1] == null ? null : decode(kv[1], "utf-8");//存储到map中if (!parameterMap.containsKey(key)) { //第一次parameterMap.put(key, new ArrayList<String>());}parameterMap.get(key).add(value);}}private String decode(String value, String enc) {try {return java.net.URLDecoder.decode(value, enc);} catch (UnsupportedEncodingException e) {// TODO Auto-generated catch blocke.printStackTrace();}return null;}public String[] getParameterValues(String key) {List<String> values = this.parameterMap.get(key);if (null == values || values.size() < 1) {return null;}return values.toArray(new String[0]);}public String getParameter(String key) {String[] values = getParameterValues(key);return values == null ? null : values[0];}public String getMethod() {return method;}public String getUrl() {return url;}public String getQueryStr() {return queryStr;}
}

Response 解析

package com.sowhat.server.core;import java.io.BufferedWriter;
import java.io.IOException;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.net.Socket;
import java.util.Date;/*** 封装返回信息：*/public class Response {private BufferedWriter bw;//正文private StringBuilder content;//协议头（状态行与请求头 回车）信息private StringBuilder headInfo;private int len; //正文的字节数private final String BLANK =" ";private final  String CRLF = "\r\n";private Response() {content =new StringBuilder();headInfo=new StringBuilder();len =0;}public Response(Socket client) {this();try {bw=new BufferedWriter(new OutputStreamWriter(client.getOutputStream()));} catch (IOException e) {e.printStackTrace();headInfo = null;}}public Response(OutputStream os) {this();bw=new BufferedWriter(new OutputStreamWriter(os));}//动态添加内容public Response print(String info) {content.append(info);len+=info.getBytes().length;return this;}public Response println(String info) {content.append(info).append(CRLF);len+=(info+CRLF).getBytes().length;return this;}// 推送响应信息public void pushToBrowser(int code) throws IOException {if(null ==headInfo) {code = 505;}createHeadInfo(code);bw.append(headInfo);bw.append(content);bw.flush();}// 构建头信息private void createHeadInfo(int code) {//1、响应行: HTTP/1.1 200 OKheadInfo.append("HTTP/1.1").append(BLANK);headInfo.append(code).append(BLANK);switch(code) {case 200:headInfo.append("OK").append(CRLF);break;case 404:headInfo.append("NOT FOUND").append(CRLF);break;    case 505:headInfo.append("SERVER ERROR").append(CRLF);break;  }//2、响应头(最后一行存在空行):headInfo.append("Date:").append(new Date()).append(CRLF);headInfo.append("Server:").append("shsxt Server/0.0.1;charset=GBK").append(CRLF);headInfo.append("Content-type:text/html").append(CRLF);headInfo.append("Content-length:").append(len).append(CRLF);headInfo.append(CRLF);       }
}

3. Servlet

Servlet接口

package com.sowhat.server.core;
/*** 服务器小脚本接口*/
public interface Servlet {void service(Request request, Response response);
}

LoginServlet

package com.sowhat.server.user;import com.sowhat.server.core.Request;
import com.sowhat.server.core.Response;
import com.sowhat.server.core.Servlet;public class LoginServlet implements Servlet {@Overridepublic void service(Request request, Response response) {response.print("<html>");response.print("<head>");response.print("<meta http-equiv=\"content-type\" content=\"text/html;charset=utf-8\">");response.print("<title>");response.print("第一个servlet");response.print("</title>");response.print("</head>");response.print("<body>");response.print("欢迎回来:" + request.getParameter("uname"));response.print("</body>");response.print("</html>");}
}

RegisterServlet

package com.sowhat.server.user;import com.sowhat.server.core.Request;
import com.sowhat.server.core.Response;
import com.sowhat.server.core.Servlet;public class RegisterServlet implements Servlet {@Overridepublic void service(Request request, Response response) {//关注业务逻辑String uname = request.getParameter("uname");String[] favs = request.getParameterValues("fav");response.print("<html>");response.print("<head>");response.print("<meta http-equiv=\"content-type\" content=\"text/html;charset=utf-8\">");response.print("<title>");response.print("注册成功");response.print("</title>");response.print("</head>");response.print("<body>");response.println("你注册的信息为:" + uname);response.println("你喜欢的类型为:");for (String v : favs) {if (v.equals("0")) {response.print("萝莉型");} else if (v.equals("1")) {response.print("豪放型");} else if (v.equals("2")) {response.print("经济节约型");}}response.print("</body>");response.print("</html>");}
}

Dispatcher

package com.sowhat.server.core;import java.io.IOException;
import java.io.InputStream;
import java.net.Socket;public class Dispatcher implements Runnable {private Socket client;private Request request; // 处理网页请求private Response response; // 返回网页请求public Dispatcher(Socket client) {this.client = client;try {//获取请求协议//获取响应协议request = new Request(client);response = new Response(client);} catch (IOException e) {e.printStackTrace();this.release();}}@Overridepublic void run() {try {if (null == request.getUrl() || request.getUrl().equals("")) {InputStream is = Thread.currentThread().getContextClassLoader().getResourceAsStream("index.html");byte[] datas = new byte[ 1024 * 1024];int len = is.read(datas);String tmp = new String(datas, 0, len);response.print(tmp);response.pushToBrowser(200);is.close();return;}Servlet servlet = WebApp.getServletFromUrl(request.getUrl());if (null != servlet) {servlet.service(request, response);//关注了状态码response.pushToBrowser(200);} else {//错误....InputStream is = Thread.currentThread().getContextClassLoader().getResourceAsStream("error.html");byte[] datas = new byte[ 1024 * 1024];int len = is.read(datas);String tmp = new String(datas, 0, len);response.print(tmp);response.pushToBrowser(404);is.close();}} catch (Exception e) {try {response.println("你好我不好，我会马上好");response.pushToBrowser(500);} catch (IOException e1) {e1.printStackTrace();}}release();}//释放资源private void release() {try {client.close();} catch (IOException e1) {e1.printStackTrace();}}
}

开启服务

package com.sowhat.server.core;import java.io.IOException;
import java.net.ServerSocket;
import java.net.Socket;/*** 开启一个服务仅此而已*/
public class Server {private ServerSocket serverSocket;private boolean isRunning;public static void main(String[] args) {Server server = new Server();server.start();}//启动服务public void start() {try {serverSocket = new ServerSocket(8888);isRunning = true;receive();} catch (IOException e) {e.printStackTrace();System.out.println("服务器启动失败....");stop();}}//接受连接处理public void receive() {while (isRunning) {try {Socket client = serverSocket.accept();System.out.println("一个客户端建立了连接....");//多线程处理new Thread(new Dispatcher(client)).start(); // 此处是 一个服务入口 重点} catch (IOException e) {e.printStackTrace();System.out.println("客户端错误");}}}//停止服务public void stop() {isRunning = false;try {this.serverSocket.close();System.out.println("服务器已停止");} catch (IOException e) {e.printStackTrace();}}
}

HTML

Error.HTML

<html><head><meta http-equiv="content-type" content="text/html;charset=utf-8">  <title>404页面</title></head><body><h1>404错误</h1></body>
</html>

index.html

<html><head><meta http-equiv="content-type" content="text/html;charset=utf-8">  <title>首页</title></head><body><h1>欢迎使用服务器简易版哈哈</h1></body>
</html>

demo

延伸

上面只是个简易版的Tomcat雏型，可大致了解到Tomcat的流程，Tomcat无非就是在基础版本上添加了各种Servlet、Request、Response、Session、Cookie、ServletContext、ServletConfig、EL、JSTL、Filter、Listener、JSP等这些东西，有空再写两章Tomcat源码底层的东西。

参考

源码密码:afnd
Tomcat入门

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手写个Tomcat雏型

前言

思路