上篇写了一个简单的Java web服务器实现，只能处理一些静态资源的请求，本篇文章实现的Servlet容器基于前面的服务器做了个小改造，增加了Servlet请求的处理。

程序执行步骤
1.创建一个ServerSocket对象；
2.调用ServerSocket对象的accept方法，等待连接，连接成功会返回一个Socket对象，否则一直阻塞等待；
3.从Socket对象中获取InputStream和OutputStream字节流，这两个流分别对应request请求和response响应；
4.处理请求：读取InputStream字节流信息，转成字符串形式，并解析，这里的解析比较简单，仅仅获取uri(统一资源标识符)信息;
5.处理响应（分两种类型，静态资源请求响应或servlet请求响应）：如果是静态资源请求，则根据解析出来的uri信息，从WEB_ROOT目录中寻找请求的资源资源文件, 读取资源文件，并将其写入到OutputStream字节流中；如果是Servlet请求，则首先生成一个URLClassLoader类加载器，加载请求的servlet类，创建servlet对象，执行service方法（往OutputStream写入响应的数据）；
6.关闭Socket对象；
7.转到步骤2，继续等待连接请求；

代码实现：
添加依赖：

<!-- https://mvnrepository.com/artifact/javax.servlet/servlet-api --> <dependency> <groupId>javax.servlet</groupId> <artifactId>servlet-api</artifactId> <version>2.3</version> </dependency>

服务器代码：

package ex02.pyrmont.first;import java.net.Socket;import java.net.ServerSocket;import java.net.InetAddress;import java.io.InputStream;import java.io.OutputStream;import java.io.IOException;import ex02.pyrmont.Request;import ex02.pyrmont.Response;import ex02.pyrmont.StaticResourceProcessor;public class HttpServer1 { // 关闭服务命令 private static final String SHUTDOWN_COMMAND = "/SHUTDOWN"; public static void main(String[] args) { HttpServer1 server = new HttpServer1(); //等待连接请求 server.await(); } public void await() { ServerSocket serverSocket = null; int port = 8080; try { //服务器套接字对象 serverSocket = new ServerSocket(port, 1, InetAddress.getByName("127.0.0.1")); } catch (IOException e) { e.printStackTrace(); System.exit(1); } // 循环等待请求 while (true) { Socket socket = null; InputStream input = null; OutputStream output = null; try { //等待连接，连接成功后，返回一个Socket对象 socket = serverSocket.accept(); input = socket.getInputStream(); output = socket.getOutputStream(); // 创建Request对象并解析 Request request = new Request(input); request.parse(); // 检查是否是关闭服务命令 if (request.getUri().equals(SHUTDOWN_COMMAND)) { break; } // 创建 Response 对象 Response response = new Response(output); response.setRequest(request); if (request.getUri().startsWith("/servlet/")) { //请求uri以/servlet/开头，表示servlet请求 ServletProcessor1 processor = new ServletProcessor1(); processor.process(request, response); } else { //静态资源请求 StaticResourceProcessor processor = new StaticResourceProcessor(); processor.process(request, response); } // 关闭 socket socket.close(); } catch (Exception e) { e.printStackTrace(); System.exit(1); } } }}

常量类：

package ex02.pyrmont;import java.io.File;public class Constants { public static final String WEB_ROOT = System.getProperty("user.dir") + File.separator + "webroot"; public static final String WEB_SERVLET_ROOT = System.getProperty("user.dir") + File.separator + "target" + File.separator + "classes"; }

Request：

package ex02.pyrmont;import java.io.InputStream;import java.io.IOException;import java.io.BufferedReader;import java.io.UnsupportedEncodingException;import java.util.Enumeration;import java.util.Locale;import java.util.Map;import javax.servlet.RequestDispatcher;import javax.servlet.ServletInputStream;import javax.servlet.ServletRequest;public class Request implements ServletRequest { private InputStream input; private String uri; public Request(InputStream input) { this.input = input; } public String getUri() { return uri; } /** * * requestString形式如下： * GET /index.html HTTP/1.1 * Host: localhost:8080 * Connection: keep-alive * Cache-Control: max-age=0 * ... * 该函数目的就是为了获取/index.html字符串 */ private String parseUri(String requestString) { int index1, index2; index1 = requestString.indexOf(' '); if (index1 != -1) { index2 = requestString.indexOf(' ', index1 + 1); if (index2 > index1) return requestString.substring(index1 + 1, index2); } return null; } //从InputStream中读取request信息，并从request中获取uri值 public void parse() { // Read a set of characters from the socket StringBuffer request = new StringBuffer(2048); int i; byte[] buffer = new byte[2048]; try { i = input.read(buffer); } catch (IOException e) { e.printStackTrace(); i = -1; } for (int j = 0; j < i; j++) { request.append((char) buffer[j]); } System.out.print(request.toString()); uri = parseUri(request.toString()); } public Object getAttribute(String attribute) { return null; } public Enumeration<?> getAttributeNames() { return null; } public String getRealPath(String path) { return null; } public RequestDispatcher getRequestDispatcher(String path) { return null; } public boolean isSecure() { return false; } public String getCharacterEncoding() { return null; } public int getContentLength() { return 0; } public String getContentType() { return null; } public ServletInputStream getInputStream() throws IOException { return null; } public Locale getLocale() { return null; } public Enumeration<?> getLocales() { return null; } public String getParameter(String name) { return null; } public Map<?, ?> getParameterMap() { return null; } public Enumeration<?> getParameterNames() { return null; } public String[] getParameterValues(String parameter) { return null; } public String getProtocol() { return null; } public BufferedReader getReader() throws IOException { return null; } public String getRemoteAddr() { return null; } public String getRemoteHost() { return null; } public String getScheme() { return null; } public String getServerName() { return null; } public int getServerPort() { return 0; } public void removeAttribute(String attribute) { } public void setAttribute(String key, Object value) { } public void setCharacterEncoding(String encoding) throws UnsupportedEncodingException { }}

Response：

package ex02.pyrmont;import java.io.OutputStream;import java.io.IOException;import java.io.FileInputStream;import java.io.FileNotFoundException;import java.io.File;import java.io.PrintWriter;import java.util.Locale;import javax.servlet.ServletResponse;import javax.servlet.ServletOutputStream;public class Response implements ServletResponse { private static final int BUFFER_SIZE = 1024; Request request; OutputStream output; PrintWriter writer; public Response(OutputStream output) { this.output = output; } public void setRequest(Request request) { this.request = request; } //将web文件写入到OutputStream字节流中 public void sendStaticResource() throws IOException { byte[] bytes = new byte[BUFFER_SIZE]; FileInputStream fis = null; try { File file = new File(Constants.WEB_ROOT, request.getUri()); fis = new FileInputStream(file); /* * HTTP Response = Status-Line(( general-header | response-header | * entity-header ) CRLF) CRLF [ message-body ] Status-Line = * HTTP-Version SP Status-Code SP Reason-Phrase CRLF */ int ch = fis.read(bytes, 0, BUFFER_SIZE); while (ch != -1) { output.write(bytes, 0, ch); ch = fis.read(bytes, 0, BUFFER_SIZE); } } catch (FileNotFoundException e) { String errorMessage = "HTTP/1.1 404 File Not Found\r\n" + "Content-Type: text/html\r\n" + "Content-Length: 23\r\n" + "\r\n" + "<h1>File Not Found</h1>"; output.write(errorMessage.getBytes()); } finally { if (fis != null) fis.close(); } } /** implementation of ServletResponse */ public void flushBuffer() throws IOException { } public int getBufferSize() { return 0; } public String getCharacterEncoding() { return null; } public Locale getLocale() { return null; } public ServletOutputStream getOutputStream() throws IOException { return null; } public PrintWriter getWriter() throws IOException { // autoflush is true, println() will flush, // but print() will not. writer = new PrintWriter(output, true); return writer; } public boolean isCommitted() { return false; } public void reset() { } public void resetBuffer() { } public void setBufferSize(int size) { } public void setContentLength(int length) { } public void setContentType(String type) { } public void setLocale(Locale locale) { }}

静态资源请求处理：

package ex02.pyrmont;import java.io.IOException;public class StaticResourceProcessor { public void process(Request request, Response response) { try { response.sendStaticResource(); } catch (IOException e) { e.printStackTrace(); } }}

Servlet请求处理：

package ex02.pyrmont.first;import java.net.URL;import java.net.URLClassLoader;import java.net.URLStreamHandler;import java.io.IOException;import javax.servlet.Servlet;import javax.servlet.ServletRequest;import javax.servlet.ServletResponse;import ex02.pyrmont.Constants;import ex02.pyrmont.Request;import ex02.pyrmont.Response;public class ServletProcessor1 { public void process(Request request, Response response) { String uri = request.getUri(); String servletName = uri.substring(uri.lastIndexOf("/") + 1); //类加载器，用于从指定JAR文件或目录加载类 URLClassLoader loader = null; try { URLStreamHandler streamHandler = null; //创建类加载器 loader = new URLClassLoader(new URL[]{new URL(null, "file:" + Constants.WEB_SERVLET_ROOT, streamHandler)}); } catch (IOException e) { System.out.println(e.toString()); } Class<?> myClass = null; try { //加载对应的servlet类 myClass = loader.loadClass(servletName); } catch (ClassNotFoundException e) { System.out.println(e.toString()); } Servlet servlet = null; try { //生产servlet实例 servlet = (Servlet) myClass.newInstance(); //执行ervlet的service方法 servlet.service((ServletRequest) request,(ServletResponse) response); } catch (Exception e) { System.out.println(e.toString()); } catch (Throwable e) { System.out.println(e.toString()); } }}

Servlet类：

import javax.servlet.*;import java.io.IOException;import java.io.PrintWriter;public class PrimitiveServlet implements Servlet { public void init(ServletConfig config) throws ServletException { System.out.println("init"); } public void service(ServletRequest request, ServletResponse response) throws ServletException, IOException { System.out.println("from service"); PrintWriter out = response.getWriter(); out.println("Hello. Roses are red."); out.print("Violets are blue."); } public void destroy() { System.out.println("destroy"); } public String getServletInfo() { return null; } public ServletConfig getServletConfig() { return null; }}

结果测试：
静态资源请求：

servlet请求（因为只是第一个字符串被刷新到浏览器，所以你不能看到第二个字符串Violets are blue。我们将在后续完善该容器）：

改进

前面实现的Servlet容器有一个严重的问题，用户在servlet里可以直接将ServletRequest、ServletResponse向下转 型为Request和Response类型，并直接调用其内部的public方法，这是一个不好的设计，改进方法是给Request、Response 增加外观类，这样，用户只能访问外观类里定义的public方法。
Request外观类

package ex02.pyrmont.second;import java.io.IOException;import java.io.BufferedReader;import java.io.UnsupportedEncodingException;import java.util.Enumeration;import java.util.Locale;import java.util.Map;import javax.servlet.RequestDispatcher;import javax.servlet.ServletInputStream;import javax.servlet.ServletRequest;import ex02.pyrmont.Request;public class RequestFacade implements ServletRequest { private ServletRequest request = null; public RequestFacade(Request request) { this.request = request; } public Object getAttribute(String attribute) { return request.getAttribute(attribute); } public Enumeration<?> getAttributeNames() { return request.getAttributeNames(); } @SuppressWarnings("deprecation") public String getRealPath(String path) { return request.getRealPath(path); } public RequestDispatcher getRequestDispatcher(String path) { return request.getRequestDispatcher(path); } public boolean isSecure() { return request.isSecure(); } public String getCharacterEncoding() { return request.getCharacterEncoding(); } public int getContentLength() { return request.getContentLength(); } public String getContentType() { return request.getContentType(); } public ServletInputStream getInputStream() throws IOException { return request.getInputStream(); } public Locale getLocale() { return request.getLocale(); } public Enumeration<?> getLocales() { return request.getLocales(); } public String getParameter(String name) { return request.getParameter(name); } public Map<?, ?> getParameterMap() { return request.getParameterMap(); } public Enumeration<?> getParameterNames() { return request.getParameterNames(); } public String[] getParameterValues(String parameter) { return request.getParameterValues(parameter); } public String getProtocol() { return request.getProtocol(); } public BufferedReader getReader() throws IOException { return request.getReader(); } public String getRemoteAddr() { return request.getRemoteAddr(); } public String getRemoteHost() { return request.getRemoteHost(); } public String getScheme() { return request.getScheme(); } public String getServerName() { return request.getServerName(); } public int getServerPort() { return request.getServerPort(); } public void removeAttribute(String attribute) { request.removeAttribute(attribute); } public void setAttribute(String key, Object value) { request.setAttribute(key, value); } public void setCharacterEncoding(String encoding) throws UnsupportedEncodingException { request.setCharacterEncoding(encoding); }}

Response外观类

package ex02.pyrmont.second;import java.io.IOException;import java.io.PrintWriter;import java.util.Locale;import javax.servlet.ServletResponse;import javax.servlet.ServletOutputStream;import ex02.pyrmont.Response;public class ResponseFacade implements ServletResponse { private ServletResponse response; public ResponseFacade(Response response) { this.response = response; } public void flushBuffer() throws IOException { response.flushBuffer(); } public int getBufferSize() { return response.getBufferSize(); } public String getCharacterEncoding() { return response.getCharacterEncoding(); } public Locale getLocale() { return response.getLocale(); } public ServletOutputStream getOutputStream() throws IOException { return response.getOutputStream(); } public PrintWriter getWriter() throws IOException { return response.getWriter(); } public boolean isCommitted() { return response.isCommitted(); } public void reset() { response.reset(); } public void resetBuffer() { response.resetBuffer(); } public void setBufferSize(int size) { response.setBufferSize(size); } public void setContentLength(int length) { response.setContentLength(length); } public void setContentType(String type) { response.setContentType(type); } public void setLocale(Locale locale) { response.setLocale(locale); }}

处理Servlet请求类：

package ex02.pyrmont.second;import java.net.URL;import java.net.URLClassLoader;import java.net.URLStreamHandler;import java.io.IOException;import javax.servlet.Servlet;import javax.servlet.ServletRequest;import javax.servlet.ServletResponse;import ex02.pyrmont.Constants;import ex02.pyrmont.Request;import ex02.pyrmont.Response;public class ServletProcessor2 { public void process(Request request, Response response) { String uri = request.getUri(); String servletName = uri.substring(uri.lastIndexOf("/") + 1); // 类加载器，用于从指定JAR文件或目录加载类 URLClassLoader loader = null; try { URLStreamHandler streamHandler = null; // 创建类加载器 loader = new URLClassLoader(new URL[] { new URL(null, "file:" + Constants.WEB_SERVLET_ROOT, streamHandler) }); } catch (IOException e) { System.out.println(e.toString()); } Class<?> myClass = null; try { // 加载对应的servlet类 myClass = loader.loadClass(servletName); } catch (ClassNotFoundException e) { System.out.println(e.toString()); } Servlet servlet = null; //给request、response增加外观类，安全性考虑，防止用户在servlet里直接将ServletRequest、ServletResponse向下转型为Request和Response类型， //并直接调用其内部的public方法，因为RequestFacade、ResponseFacade里不会有parse、sendStaticResource等方法； RequestFacade requestFacade = new RequestFacade(request); ResponseFacade responseFacade = new ResponseFacade(response); try { servlet = (Servlet) myClass.newInstance(); servlet.service((ServletRequest) requestFacade, (ServletResponse) responseFacade); } catch (Exception e) { System.out.println(e.toString()); } catch (Throwable e) { System.out.println(e.toString()); } }}

其它代码与前面实现的Servlet容器基本一致。
验证程序，分别请求静态资源和Servlet，发现结果与前面实现的容器一致；

参考资料：《深入剖析Tomcat》

@author 风一样的码农

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