servlet三种方式实现servlet接口

简单介绍

Servlet接口实现类

1、Servlet接口SUN公司定义了两个默认实现类，分别为：GenericServlet、HttpServlet。

2、HttpServlet指能够处理HTTP请求的servlet，它在原有Servlet接口上添加了一些与HTTP协议处理方法，它比Servlet接口的功能更为强大。因此开发人员在编写Servlet时，通常应继承这个类，而避免直接去实现Servlet接口。

3、HttpServlet在实现Servlet接口时，覆写了service方法，该方法体内的代码会自动判断用户的请求方式，如为GET请求，则调用HttpServlet的doGet方法，如为Post请求，则调用doPost方法。因此，开发人员在编写Servlet时，通常只需要覆写doGet或doPost方法，而不要去覆写service方法。

接口分离原则：

将一个包含多功能的单一接口根据函数功能分离称多个独立的接口，同时每个接口都有自己特有的、有意义的、具有实际哦那功能的修饰器。
   多重接口修饰：
        每个修饰器设计时都需要首先实现他要修饰的接口，可以配合应用适配器和修饰器这两个模式来构建多重修饰器，同时也能保证代码量最少。
客户端构建：
   为客户端提供接口实例的方式一定程度上取决于接口实现的数目。如果每个接口都有自己特有的实现，那就需要构造所有实现的实例并提供给客户端。或者如果所有的接口的实现都包含在单个类中，那么只需要构建该类的实例就能够满足客户端的所有依赖。
   1、多接口、多实例：
       控制器类：将所有方法整合到控制器类中（构造函数传入参数为各个接口）。控制器类中的每个方法都需要一个不同的接口来执行他的功能。
   2、单接口、单实例：
       在单个类中继承并实现所有接口。这样将每个接口的实现方法都整合到一个类中。（一般用于叶子实现类）

Servlet的作用：

1.接收请求数据

2.处理请求

3.完成响应

Servlet接口中的五大方法：

其中有三个是生命周期方法：

1.void init(ServletConfig).当Servlet对象被服务器创建时调用，仅调用一次。

2.void service(ServletRequest, ServletResponse).可被服务器调用多次。

3.void destroy().服务器关闭连接之前调用，仅一次。

另外的两个：

4.ServletConfig getServletConfig()

5.String getServletInfo()

Servlet代码源

package javax.servlet;import java.io.IOException;public interface Servlet {void init(ServletConfig var1) throws ServletException;ServletConfig getServletConfig();void service(ServletRequest var1, ServletResponse var2) throws ServletException, IOException;String getServletInfo();void destroy();
}

View Code

HttpServlet代码源

package javax.servlet.http;import java.io.IOException;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.text.MessageFormat;
import java.util.Enumeration;
import java.util.ResourceBundle;
import javax.servlet.DispatcherType;
import javax.servlet.GenericServlet;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;public abstract class HttpServlet extends GenericServlet {private static final long serialVersionUID = 1L;private static final String METHOD_DELETE = "DELETE";private static final String METHOD_HEAD = "HEAD";private static final String METHOD_GET = "GET";private static final String METHOD_OPTIONS = "OPTIONS";private static final String METHOD_POST = "POST";private static final String METHOD_PUT = "PUT";private static final String METHOD_TRACE = "TRACE";private static final String HEADER_IFMODSINCE = "If-Modified-Since";private static final String HEADER_LASTMOD = "Last-Modified";private static final String LSTRING_FILE = "javax.servlet.http.LocalStrings";private static final ResourceBundle lStrings = ResourceBundle.getBundle("javax.servlet.http.LocalStrings");public HttpServlet() {}protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {String protocol = req.getProtocol();String msg = lStrings.getString("http.method_get_not_supported");if (protocol.endsWith("1.1")) {resp.sendError(405, msg);} else {resp.sendError(400, msg);}}protected long getLastModified(HttpServletRequest req) {return -1L;}protected void doHead(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {if (DispatcherType.INCLUDE.equals(req.getDispatcherType())) {this.doGet(req, resp);} else {NoBodyResponse response = new NoBodyResponse(resp);this.doGet(req, response);response.setContentLength();}}protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {String protocol = req.getProtocol();String msg = lStrings.getString("http.method_post_not_supported");if (protocol.endsWith("1.1")) {resp.sendError(405, msg);} else {resp.sendError(400, msg);}}protected void doPut(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {String protocol = req.getProtocol();String msg = lStrings.getString("http.method_put_not_supported");if (protocol.endsWith("1.1")) {resp.sendError(405, msg);} else {resp.sendError(400, msg);}}protected void doDelete(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {String protocol = req.getProtocol();String msg = lStrings.getString("http.method_delete_not_supported");if (protocol.endsWith("1.1")) {resp.sendError(405, msg);} else {resp.sendError(400, msg);}}private static Method[] getAllDeclaredMethods(Class<?> c) {if (c.equals(HttpServlet.class)) {return null;} else {Method[] parentMethods = getAllDeclaredMethods(c.getSuperclass());Method[] thisMethods = c.getDeclaredMethods();if (parentMethods != null && parentMethods.length > 0) {Method[] allMethods = new Method[parentMethods.length + thisMethods.length];System.arraycopy(parentMethods, 0, allMethods, 0, parentMethods.length);System.arraycopy(thisMethods, 0, allMethods, parentMethods.length, thisMethods.length);thisMethods = allMethods;}return thisMethods;}}protected void doOptions(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {Method[] methods = getAllDeclaredMethods(this.getClass());boolean ALLOW_GET = false;boolean ALLOW_HEAD = false;boolean ALLOW_POST = false;boolean ALLOW_PUT = false;boolean ALLOW_DELETE = false;boolean ALLOW_TRACE = true;boolean ALLOW_OPTIONS = true;Class clazz = null;try {clazz = Class.forName("org.apache.catalina.connector.RequestFacade");Method getAllowTrace = clazz.getMethod("getAllowTrace", (Class[])null);ALLOW_TRACE = (Boolean)getAllowTrace.invoke(req, (Object[])null);} catch (NoSuchMethodException | SecurityException | IllegalAccessException | IllegalArgumentException | InvocationTargetException | ClassNotFoundException var14) {;}for(int i = 0; i < methods.length; ++i) {Method m = methods[i];if (m.getName().equals("doGet")) {ALLOW_GET = true;ALLOW_HEAD = true;}if (m.getName().equals("doPost")) {ALLOW_POST = true;}if (m.getName().equals("doPut")) {ALLOW_PUT = true;}if (m.getName().equals("doDelete")) {ALLOW_DELETE = true;}}String allow = null;if (ALLOW_GET) {allow = "GET";}if (ALLOW_HEAD) {if (allow == null) {allow = "HEAD";} else {allow = allow + ", HEAD";}}if (ALLOW_POST) {if (allow == null) {allow = "POST";} else {allow = allow + ", POST";}}if (ALLOW_PUT) {if (allow == null) {allow = "PUT";} else {allow = allow + ", PUT";}}if (ALLOW_DELETE) {if (allow == null) {allow = "DELETE";} else {allow = allow + ", DELETE";}}if (ALLOW_TRACE) {if (allow == null) {allow = "TRACE";} else {allow = allow + ", TRACE";}}if (ALLOW_OPTIONS) {if (allow == null) {allow = "OPTIONS";} else {allow = allow + ", OPTIONS";}}resp.setHeader("Allow", allow);}protected void doTrace(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {String CRLF = "\r\n";StringBuilder buffer = (new StringBuilder("TRACE ")).append(req.getRequestURI()).append(" ").append(req.getProtocol());Enumeration reqHeaderEnum = req.getHeaderNames();while(reqHeaderEnum.hasMoreElements()) {String headerName = (String)reqHeaderEnum.nextElement();buffer.append(CRLF).append(headerName).append(": ").append(req.getHeader(headerName));}buffer.append(CRLF);int responseLength = buffer.length();resp.setContentType("message/http");resp.setContentLength(responseLength);ServletOutputStream out = resp.getOutputStream();out.print(buffer.toString());out.close();}protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {String method = req.getMethod();long lastModified;if (method.equals("GET")) {lastModified = this.getLastModified(req);if (lastModified == -1L) {this.doGet(req, resp);} else {long ifModifiedSince;try {ifModifiedSince = req.getDateHeader("If-Modified-Since");} catch (IllegalArgumentException var9) {ifModifiedSince = -1L;}if (ifModifiedSince < lastModified / 1000L * 1000L) {this.maybeSetLastModified(resp, lastModified);this.doGet(req, resp);} else {resp.setStatus(304);}}} else if (method.equals("HEAD")) {lastModified = this.getLastModified(req);this.maybeSetLastModified(resp, lastModified);this.doHead(req, resp);} else if (method.equals("POST")) {this.doPost(req, resp);} else if (method.equals("PUT")) {this.doPut(req, resp);} else if (method.equals("DELETE")) {this.doDelete(req, resp);} else if (method.equals("OPTIONS")) {this.doOptions(req, resp);} else if (method.equals("TRACE")) {this.doTrace(req, resp);} else {String errMsg = lStrings.getString("http.method_not_implemented");Object[] errArgs = new Object[]{method};errMsg = MessageFormat.format(errMsg, errArgs);resp.sendError(501, errMsg);}}private void maybeSetLastModified(HttpServletResponse resp, long lastModified) {if (!resp.containsHeader("Last-Modified")) {if (lastModified >= 0L) {resp.setDateHeader("Last-Modified", lastModified);}}}public void service(ServletRequest req, ServletResponse res) throws ServletException, IOException {HttpServletRequest request;HttpServletResponse response;try {request = (HttpServletRequest)req;response = (HttpServletResponse)res;} catch (ClassCastException var6) {throw new ServletException("non-HTTP request or response");}this.service(request, response);}
}

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GenericServlet代码源

package javax.servlet;import java.io.IOException;
import java.io.Serializable;
import java.util.Enumeration;public abstract class GenericServlet implements Servlet, ServletConfig, Serializable {private static final long serialVersionUID = 1L;private transient ServletConfig config;public GenericServlet() {}public void destroy() {}public String getInitParameter(String name) {return this.getServletConfig().getInitParameter(name);}public Enumeration<String> getInitParameterNames() {return this.getServletConfig().getInitParameterNames();}public ServletConfig getServletConfig() {return this.config;}public ServletContext getServletContext() {return this.getServletConfig().getServletContext();}public String getServletInfo() {return "";}public void init(ServletConfig config) throws ServletException {this.config = config;this.init();}public void init() throws ServletException {}public void log(String msg) {this.getServletContext().log(this.getServletName() + ": " + msg);}public void log(String message, Throwable t) {this.getServletContext().log(this.getServletName() + ": " + message, t);}public abstract void service(ServletRequest var1, ServletResponse var2) throws ServletException, IOException;public String getServletName() {return this.config.getServletName();}
}

View Code

实现接口代码：

package com.wbg;import javax.servlet.*;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;@WebServlet("/MyServlet")
public class MyServlet implements Servlet {@Overridepublic void init(ServletConfig servletConfig) throws ServletException {System.out.println("初始化servlet");}@Overridepublic ServletConfig getServletConfig() {System.out.println("getServletConfig()");return null;}@Overridepublic void service(ServletRequest servletRequest, ServletResponse servletResponse) throws ServletException, IOException {System.out.println("正在销毁");}@Overridepublic String getServletInfo() {System.out.println("getServletInfo()");return null;}@Overridepublic void destroy() {System.out.println("正在销毁");}
}

浏览器访问servlet时，需要将servlet与路径绑定，需要在web.xml中对servlet进行配置：

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"version="4.0"><servlet>

 <servlet-name>testservlet</servlet-name>

        <servlet-class>com.wbg.testservlet</servlet-class></servlet>
</web-app>

实现接口的意义:

1、接口和实现分离给软件系统提供了无限的想像空间，才使得软件世界如此丰富多彩。

2、接口和实现分离使得多态变为可能

3、接口和实现分离使得解耦变为可能

4、接口和实现分离使得组合更有意义

5、接口和实现分离使得设计模式变为可能，才能衍生出23种设计模式。

简单的说接口和实现分离给软件系统提供了无限的想象空间、多态变为可能、解耦变为可能、组合更有意义、设计模式变为可能，才能衍生出23钟设计模式(创建型、结构型、行为型)

posted @ 2018-08-13 08:20 韦邦杠阅读(...) 评论(...) 编辑收藏