基于Java web服务器简单实现一个Servlet容器
作者：风一样的码农
这篇文章主要为大家详细介绍了基于Java web服务器简单实现一个Servlet容器，感兴趣的小伙伴们可以参考一下
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());
}
/* implementation of the ServletRequest */
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 {
/* request.getUri has been replaced by request.getRequestURI */
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;
}
/* implementation of the ServletRequest */
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
以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持脚本之家。