Java學習路線-48：Servlet學習

課時1 Servlet是什么

Servlet作用是處理請求

接收請求

處理請求

完成響應

課時2 實現(xiàn)Servlet方式

依賴

javax.servlet javax.servlet-api 4.0.1 provided

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實現(xiàn)方式

// 實現(xiàn)接口： javax.servlet.Servlet // 繼承類： javax.servlet.GenericServlet // 繼承類： javax.servlet.HttpServlet

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繼承示例

AServlet.java

import javax.servlet.*; import java.io.IOException; public class AServlet implements Servlet{ // 創(chuàng)建時執(zhí)行 @Override public void init(ServletConfig servletConfig) throws ServletException { } // 獲取配置信息 @Override public ServletConfig getServletConfig() { return null; } // 處理請求 @Override public void service(ServletRequest servletRequest, ServletResponse servletResponse) throws ServletException, IOException { } // 獲取servlet信息 @Override public String getServletInfo() { return null; } // 銷毀前調(diào)用 @Override public void destroy() { } }

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課時3 Servlet的生命周期

生命周期

init 實例化調(diào)用 service 每次處理請求都調(diào)用 destroy 銷毀調(diào)用

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特性

（1）單例，每個類只有一個對象

（2）線程不安全，效率最高

Servlet類由用戶自定義，對象由服務器來創(chuàng)建，并有服務器調(diào)用對應的方法

瀏覽器訪問Servlet

給Servlet配置一個路徑

web.xml

demo AServlet demo demo

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目錄結(jié)構(gòu)

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

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課時4 ServletConfig介紹

interface ServletConfig{ // 獲取servlet-name中的內(nèi)容 String getServletName() // 獲取Servlet上下文對象 ServletContext getServletContext() // 獲取指定初始化參數(shù)值 String getInitParameter(String name) // 獲取所有初始化參數(shù)值 Enumeration getInitParameterNames() }

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name Tom

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獲取參數(shù)

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

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課時5 ServletRequest和Servletresponse對象

interface ServletRequest; interface ServletResponse;

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課時6 GenericServlet介紹

GenericServlet可以只覆寫service方法，不用全寫

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(); } // 實現(xiàn)此方法，初始化后可以調(diào)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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課時7 HttpServlet介紹

源碼

package javax.servlet.http; public abstract class HttpServlet extends GenericServlet { // 重寫 protected void doGet(HttpServletRequest req, HttpServletResponse resp); // 重寫 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請求

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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課時8 Servlet的細節(jié)

1、非線程安全

一個Servlet類只有一個實例對象，不是線程安全的，工作效率高

（1）不要在Servlet中創(chuàng)建成員，創(chuàng)建局部變量即可

（2）可以創(chuàng)建無狀態(tài)成員

（3）可以創(chuàng)建有狀態(tài)的成員，但是狀態(tài)必須為只讀

2、創(chuàng)建時啟動

默認情況下，服務器會在第一次訪問Servlet時創(chuàng)建實例對象

給load-on-startup設置一個非負整數(shù)

正數(shù)的值越小，啟動該servlet的優(yōu)先級越高

可以配置創(chuàng)建時啟動

servletName 0

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3、url-pattern

可以有多個訪問路徑

可以使用前綴或者后綴通配符*

servletName /demo/* *.do /*

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課時9 在conf下的web.xml文件內(nèi)容介紹

${CATALINA_HOME}/conf/web.xml

default / 30 xml application/xml

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課時10 Servlet與反射

Servlet通過反射，獲取配置文件的類名，進行實例化和方法調(diào)用

課時11 ServletContext概述

一個項目只有一個ServletContext對象

可以在多個Servlet中傳遞對象

Tomcat啟動時創(chuàng)建，關(guān)閉時銷毀

課時12 獲取ServletContext對象

獲取ServletContext

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

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課時13 演示ServletContext

域?qū)ο? 在多個Servlet中傳遞數(shù)據(jù)

class ServletContext{ // 設置 多次調(diào)用會覆蓋 void setAttribute(String name, Object vlaue); // 獲取 Object getAttribute(String name); // 移除 void removeAttribute(String name); // 獲取全部屬性名稱 Enumeration getAttributeNames(); }

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例如: AServlet的數(shù)據(jù)可以傳遞到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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課時14 ServletContext獲取公共的初始化參數(shù)

Servlet只能獲取自己的初始化參數(shù)

ServletContext獲取公共的初始化參數(shù)

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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課時15 ServletContext獲取資源相關(guān)方法

以webapp文根目錄

ServletContext context = getServletContext(); // 獲取絕對路徑 String path = context.getRealPath("/index.html"); // 獲取文件后轉(zhuǎn)為輸入流 InputStream in = context.getResourceAsStream("/index.html"); // 獲取目錄下的文件 Set set = context.getResourcePaths("/"); // [/hello.html, /WEB-INF/]

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課時16 網(wǎng)站訪問量統(tǒng)計小案例

使用ServletContext對象共享統(tǒng)計數(shù)據(jù)

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; // 第一次訪問 } else { count++; } response.setContentType("text/html; charset=UTF-8"); response.getWriter().println("

第"+count+"次訪問

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課時17 獲取類路徑下的資源

依賴

commons-io commons-io 2.6

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代碼實例

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、相對于.class所在目錄 InputStream input1 = clazz.getResourceAsStream("1.txt"); System.out.println(IOUtils.toString(input1, StandardCharsets.UTF_8)); // 2、相對于/classes InputStream input2 = clazz.getResourceAsStream("/2.txt"); System.out.println(IOUtils.toString(input2, StandardCharsets.UTF_8)); ClassLoader loader = clazz.getClassLoader(); // 3、相對于/classes InputStream input3 = loader.getResourceAsStream("3.txt"); System.out.println(IOUtils.toString(input3, StandardCharsets.UTF_8)); } }

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課時18 BaseServlet

一個Servlet中可以有多個請求處理方法

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); // 通過參數(shù)獲取方法 Class clazz = this.getClass(); Method method = null; try { method = clazz.getMethod(methodName, HttpServletRequest.class, HttpServletResponse.class); } catch (NoSuchMethodException e) { throw new RuntimeException("方法獲取失敗"); } // 調(diào)用方法 try { method.invoke(this, req, resp); } catch (Exception e) { throw new RuntimeException("調(diào)用失敗"); } } }

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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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調(diào)用時傳入查詢參數(shù)

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

Java Servlet

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