Java学习路线-48：Servlet学习

课时1 Servlet是什么

Servlet作用是处理请求

接收请求

处理请求

完成响应

课时2 实现Servlet方式

依赖

javax.servlet javax.servlet-api 4.0.1 provided

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实现方式

// 实现接口： javax.servlet.Servlet // 继承类： javax.servlet.GenericServlet // 继承类： javax.servlet.HttpServlet

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继承示例

AServlet.java

import javax.servlet.*; import java.io.IOException; public class AServlet implements Servlet{ // 创建时执行 @Override public void init(ServletConfig servletConfig) throws ServletException { } // 获取配置信息 @Override public ServletConfig getServletConfig() { return null; } // 处理请求 @Override public void service(ServletRequest servletRequest, ServletResponse servletResponse) throws ServletException, IOException { } // 获取servlet信息 @Override public String getServletInfo() { return null; } // 销毁前调用 @Override public void destroy() { } }

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课时3 Servlet的生命周期

生命周期

init 实例化调用 service 每次处理请求都调用 destroy 销毁调用

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特性

（1）单例，每个类只有一个对象

（2）线程不安全，效率最高

Servlet类由用户自定义，对象由服务器来创建，并有服务器调用对应的方法

浏览器访问Servlet

给Servlet配置一个路径

web.xml

demo AServlet demo demo

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目录结构

webapp └── WEB-INF ├── classes │ └── AServlet.class └── web.xml

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课时4 ServletConfig介绍

interface ServletConfig{ // 获取servlet-name中的内容 String getServletName() // 获取Servlet上下文对象 ServletContext getServletContext() // 获取指定初始化参数值 String getInitParameter(String name) // 获取所有初始化参数值 Enumeration getInitParameterNames() }

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name Tom

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获取参数

@Override public void init(ServletConfig servletConfig) throws ServletException { System.out.println(servletConfig.getInitParameter("name")); }

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课时5 ServletRequest和Servletresponse对象

interface ServletRequest; interface ServletResponse;

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课时6 GenericServlet介绍

GenericServlet可以只覆写service方法，不用全写

基本原理

import javax.servlet.*; import java.io.IOException; public class AServlet implements Servlet { private ServletConfig config = null; @Override public void init(ServletConfig servletConfig) { this.config = servletConfig; this.init(); } // 实现此方法，初始化后可以调用 public void init() { } @Override public ServletConfig getServletConfig() { return this.config; } @Override public void service(ServletRequest servletRequest, ServletResponse servletResponse) throws ServletException, IOException { } @Override public String getServletInfo() { return null; } @Override public void destroy() { } }

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使用示例

import javax.servlet.*; import java.io.IOException; public class AServlet extends GenericServlet { @Override public void service(ServletRequest servletRequest, ServletResponse servletResponse) throws IOException { servletResponse.getWriter().write("

hello

"); } }

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课时7 HttpServlet介绍

源码

package javax.servlet.http; public abstract class HttpServlet extends GenericServlet { // 重写 protected void doGet(HttpServletRequest req, HttpServletResponse resp); // 重写 protected void doPost(HttpServletRequest req, HttpServletResponse resp); protected void service(HttpServletRequest req, HttpServletResponse resp); public void service(ServletRequest req, ServletResponse res){ if (req instanceof HttpServletRequest && res instanceof HttpServletResponse) { HttpServletRequest request = (HttpServletRequest)req; HttpServletResponse response = (HttpServletResponse)res; this.service(request, response); } else { throw new ServletException("non-HTTP request or response"); } } }

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使用示例: 接收GET请求

import javax.servlet.*; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import java.io.IOException; public class AServlet extends HttpServlet { @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { resp.getWriter().write("

hello

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课时8 Servlet的细节

1、非线程安全

一个Servlet类只有一个实例对象，不是线程安全的，工作效率高

（1）不要在Servlet中创建成员，创建局部变量即可

（2）可以创建无状态成员

（3）可以创建有状态的成员，但是状态必须为只读

2、创建时启动

默认情况下，服务器会在第一次访问Servlet时创建实例对象

给load-on-startup设置一个非负整数

正数的值越小，启动该servlet的优先级越高

可以配置创建时启动

servletName 0

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3、url-pattern

可以有多个访问路径

可以使用前缀或者后缀通配符*

servletName /demo/* *.do /*

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课时9 在conf下的web.xml文件内容介绍

${CATALINA_HOME}/conf/web.xml

default / 30 xml application/xml

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课时10 Servlet与反射

Servlet通过反射，获取配置文件的类名，进行实例化和方法调用

课时11 ServletContext概述

一个项目只有一个ServletContext对象

可以在多个Servlet中传递对象

Tomcat启动时创建，关闭时销毁

课时12 获取ServletContext对象

获取ServletContext

class ServeletConfig{ ServletContext getServletContext(); } class GenericServlet{ ServletContext getServletContext(); }

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课时13 演示ServletContext

域对象: 在多个Servlet中传递数据

class ServletContext{ // 设置 多次调用会覆盖 void setAttribute(String name, Object vlaue); // 获取 Object getAttribute(String name); // 移除 void removeAttribute(String name); // 获取全部属性名称 Enumeration getAttributeNames(); }

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例如: AServlet的数据可以传递到BServlet

AServlet.java

package com.pengshiyu; import javax.servlet.ServletContext; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import java.io.IOException; public class AServlet extends HttpServlet { @Override protected void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException { String name = request.getParameter("name"); ServletContext context = getServletContext(); context.setAttribute("name", name); response.getWriter().write("

" + name +"

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BServlet.java

package com.pengshiyu; import javax.servlet.ServletContext; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import java.io.IOException; public class BServlet extends HttpServlet { @Override protected void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException { ServletContext context = getServletContext(); String name = (String)context.getAttribute("name"); response.getWriter().println(name); } }

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课时14 ServletContext获取公共的初始化参数

Servlet只能获取自己的初始化参数

ServletContext获取公共的初始化参数

key value

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package com.pengshiyu; import javax.servlet.ServletContext; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import java.io.IOException; public class BServlet extends HttpServlet { @Override protected void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException { ServletContext context = getServletContext(); String name = context.getInitParameter("key"); response.getWriter().println(name); } }

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课时15 ServletContext获取资源相关方法

以webapp文根目录

ServletContext context = getServletContext(); // 获取绝对路径 String path = context.getRealPath("/index.html"); // 获取文件后转为输入流 InputStream in = context.getResourceAsStream("/index.html"); // 获取目录下的文件 Set set = context.getResourcePaths("/"); // [/hello.html, /WEB-INF/]

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课时16 网站访问量统计小案例

使用ServletContext对象共享统计数据

package com.pengshiyu; import javax.servlet.ServletContext; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import java.io.IOException; public class BServlet extends HttpServlet { @Override protected void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException { ServletContext context = getServletContext(); Integer count = (Integer) context.getAttribute("count"); if (count == null) { count = 1; // 第一次访问 } else { count++; } response.setContentType("text/html; charset=UTF-8"); response.getWriter().println("

第"+count+"次访问

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课时17 获取类路径下的资源

依赖

commons-io commons-io 2.6

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代码实例

package com.pengshiyu; import org.apache.commons.io.IOUtils; import java.io.IOException; import java.io.InputStream; import java.nio.charset.StandardCharsets; public class Demo { public static void main(String[] args) throws IOException { Class clazz = Demo.class; // 1、相对于.class所在目录 InputStream input1 = clazz.getResourceAsStream("1.txt"); System.out.println(IOUtils.toString(input1, StandardCharsets.UTF_8)); // 2、相对于/classes InputStream input2 = clazz.getResourceAsStream("/2.txt"); System.out.println(IOUtils.toString(input2, StandardCharsets.UTF_8)); ClassLoader loader = clazz.getClassLoader(); // 3、相对于/classes InputStream input3 = loader.getResourceAsStream("3.txt"); System.out.println(IOUtils.toString(input3, StandardCharsets.UTF_8)); } }

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课时18 BaseServlet

一个Servlet中可以有多个请求处理方法

BaseServlet.java

package com.pengshiyu; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import java.io.IOException; import java.lang.reflect.Method; public class BaseServlet extends HttpServlet { @Override protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { String methodName = req.getParameter("method"); if(methodName == null || methodName.trim().isEmpty()){ throw new RuntimeException("method is null or empty"); } System.out.println(methodName); // 通过参数获取方法 Class clazz = this.getClass(); Method method = null; try { method = clazz.getMethod(methodName, HttpServletRequest.class, HttpServletResponse.class); } catch (NoSuchMethodException e) { throw new RuntimeException("方法获取失败"); } // 调用方法 try { method.invoke(this, req, resp); } catch (Exception e) { throw new RuntimeException("调用失败"); } } }

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AServlet.java

package com.pengshiyu; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import java.io.IOException; public class AServlet extends BaseServlet { public void getAge(HttpServletRequest request, HttpServletResponse response) throws IOException { response.getWriter().print("getAge"); } public void getName(HttpServletRequest request, HttpServletResponse response) throws IOException { response.getWriter().print("getName"); } }

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调用时传入查询参数

http://localhost:8080/demo/hello?method=getAge

Java Servlet

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