javaweb -- 4、Servlet系列之ServletContext、ServletConfig、JSP

谁践踏了优雅 2023-03-01 05:51 34阅读 0赞

**目录**

7.1：Servlet系列之ServletContext（程序上下文）和ServletConfig（程序配置）

2、ServletConfig：（程序配置）

8.1： Servlet系列之JSP介绍

1、Servlet与JSP的优点与缺点

2、动态生成网页数据：

3、创建JSP同时也生成一个java类文件

4、Luyten软件可以查看配置文件内容：

5、（需要注意的地方）

8.2：

1、（输出变量）

2、（输出整个方法）

--------------------

# **7** #

## **7.1****：****Servlet****系列之ServletContext（程序上下文）和ServletConfig（程序配置）** ##

**Servlet****Context****：**

**         **不同用户发起的请求获取到的都是同一个对象， 该对象由用户共同拥有

**API：**![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NTA0MjU2OQ_size_16_color_FFFFFF_t_70][]

![20200722134436537.png][]![20200722134439236.png][]

**java****文件：****Servlet****Context****Servlet****（上下文程序）**

*      作用：
    *          不同用户发起的请求获取同一个对象
    *      特点：
    *          1、由服务器创建
    *          2、所有用户共享同一个ServletContext对象
    *          3、所有的servlet都可以访问到同一个ServletContext中的属性
    *          4、每一个web项目对应的是一个ServletContext
    public class ServletContextServlet extends HttpServlet {
        @Override
        protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
            this.doGet(request,response);
        }
        @Override
        protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    
    //获取servletContext对象方式：
            //方式一（用得较多）
            ServletContext context = this.getServletContext();
            //方式二
            ServletContext context1 = this.getServletConfig().getServletContext();
            //方式三
            ServletContext context2 = request.getSession().getServletContext();
    
            System.out.println(context==context1);
            System.out.println(context == context2);
            System.out.println(context1==context2);

![20200722134506611.png][]![2020072213450967.png][]

//设置属性值（需要配合下面的java代码ServletContextServlet2）
            context.setAttribute("111","zhangsan");
    //从web.xml中获取参数值（下面有代码解释）
            String value = context.getInitParameter("beijing");
            System.out.println(value);

//获取某个文件的路径![20200722134528352.png][]![20200722134534140.png][]

String path = context.getRealPath("web.xml");
            System.out.println(path);

//获取web项目的上下文路径![20200722134602149.png][]![20200722134613707.png][]

String path2 = context.getContextPath();
            System.out.println(path2); 
        }
    }

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NTA0MjU2OQ_size_16_color_FFFFFF_t_70 1][]

**web.xml****文件：**

<servlet>
 <servlet-name>ServletContextServlet</servlet-name>
 <servlet-class>com.mashibing.ServletContextServlet</servlet-class>
 </servlet>
 <servlet-mapping>
 <servlet-name>ServletContextServlet</servlet-name>
 <url-pattern>/context</url-pattern>
 </servlet-mapping>

**java****文件：****Servlet****Context****Servlet2****（上下文程序2）**

![20200722134718115.png][]![20200722134721870.png][]

@WebServlet(name = "ServletContextServlet2")
    public class ServletContextServlet2 extends HttpServlet {
        @Override
        protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
            this.doGet(request,response);
        }
        @Override
        protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
            ServletContext context = this.getServletContext();
            String value = (String) context.getAttribute("111"); //改其他数字会null
            System.out.println(value);
        }
    }

**web.xml****文件：**

<servlet>
 <servlet-name>ServletContextServlet2</servlet-name>
 <servlet-class>com.mashibing.ServletContextServlet2</servlet-class>
 </servlet>
 <servlet-mapping>
 <servlet-name>ServletContextServlet2</servlet-name>
 <url-pattern>/context2</url-pattern>
 </servlet-mapping>

**第一次启动浏览器：**![2020072213480581.png][]![20200722134808900.png][]

**第二次启动浏览器：**![20200722134815313.png][]![20200722134817936.png][]

**（第一种，全局）//从web.xml中获取参数值：必须写最上面**

（使用ServletContext对象可以获取web.xml中的全局配置文件，在web.xml中每个Servlet也可以进行单独的配置）

![20200722134836470.png][]![20200722134839205.png][]

<context-param>
 <param-name>beijing</param-name>
 <param-value>beautiful</param-value>
 </context-param>
 ====================================================================
 <context-param>
 <param-name>···</param-name>
 <param-value>···</param-value>
 </context-param>
 ···

**网站计数器案例：****用户访问次数，（刷新也算）**

**java****文件：****NumServlet****（计数服务）**

![2020072213491639.png][]![20200722134918979.png][]

public class NumServlet extends HttpServlet {
 @Override
 protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
 this.doGet(request,response);
 }
 @Override
 protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
 
 request.setCharacterEncoding("utf-8");
 response.setContentType("text/html;charset=utf-8");
 
 //获取Servletcontext对象
 ServletContext context = this.getServletContext();
 //获取属性值
 Integer num = (Integer) context.getAttribute("num");
 if(num==null){
 context.setAttribute("num",1); //没访问进去，次数显示1
 }else{
 num++; //访问成功，计数加1
 //将num设置会servletcontext对象中
 context.setAttribute("num",num);
 }
 //获取输出对象
 PrintWriter out = response.getWriter();
 out.write("<html>");
 out.write("<head>");
 out.write("</head>");
 out.write("<body>");
 out.write("用户访问的次数是"+context.getAttribute("num")+"次");
 out.write("</body>");
 out.write("</html>");
 }
 }

**web.xml****文件：**

<servlet>
 <servlet-name>NumServlet</servlet-name>
 <servlet-class>com.context.NumServlet</servlet-class>
 </servlet>
 <servlet-mapping>
 <servlet-name>NumServlet</servlet-name>
 <url-pattern>/num</url-pattern>
 </servlet-mapping>

![20200722134957793.png][]**（刷新也算访问）**

**新建项目：**

### **2****、Servlet****Config****：****（程序配置）** ###

![2020072213501236.png][]![20200722135014665.png][]

**java****文件：****Servlet****Config****Servlet****（程序配置）**

public class ServletConfigServlet extends HttpServlet {
        @Override
        protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
            this.doGet(request,response);
        }
        @Override
        protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    //获取对象
            ServletConfig config = this.getServletConfig();
            String value = config.getInitParameter("china");
            System.out.println(value);

![20200722135042566.png][]![20200722135045207.png][]

//获取所有的key
 Enumeration<String> initParameterNames = config.getInitParameterNames();
 while (initParameterNames.hasMoreElements()){
 String key = initParameterNames.nextElement();
 String value2 = config.getInitParameter(key);
 System.out.println(key+"----"+value2);
 }
 }
 }

![20200722135127308.png][]![20200722135130729.png][]

**（第一种，局部）//从web.xml中获取参数值：必须写最上面**

作用：方便每一个servlet获取自己单独的属性配置
 特点：每一个servlet单独拥有一个servletConfig对象
 
 <servlet>
 <servlet-name>ServletConfigServlet</servlet-name>
 <servlet-class>com.mashibing.ServletConfigServlet</servlet-class>
 <init-param>
 <param-name>china</param-name>
 <param-value>beijing</param-value>
 </init-param>
 
 <init-param>
 <param-name>hebei</param-name>
 <param-value>shijiazhuang</param-value>
 </init-param>
 </servlet>
 
 <servlet-mapping>
 <servlet-name>ServletConfigServlet</servlet-name>
 <url-pattern>/config</url-pattern>
 </servlet-mapping>

# 8 #

## 8.1： Servlet系列之JSP介绍 ##

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NTA0MjU2OQ_size_16_color_FFFFFF_t_70 2][]

### 1、Servlet与JSP的优点与缺点 ![20200722135238813.png][] ###

Servlet:
    
        优点：逻辑处理方便
    
        缺点：界面表现麻烦
    
    JSP：
    
        优点：界面表现方便
    
        缺点：逻辑处理麻烦

### 2、动态生成网页数据： ###

常见的几种动态网页技术：
    
        JSP(Java Server Page)
    
        ASP(Active Server Page)
    
        PHP(Hypertext Preprocessor) 超级文本预处理语言

### 3、创建JSP同时也生成一个java类文件 ###

![20200722135332462.png][]

java类中：

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NTA0MjU2OQ_size_16_color_FFFFFF_t_70 3][]

### 4、Luyten软件可以查看配置文件内容： ###

![20200722135442904.png][]![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NTA0MjU2OQ_size_16_color_FFFFFF_t_70 4][]

### 5、（需要注意的地方） ###

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NTA0MjU2OQ_size_16_color_FFFFFF_t_70 5][]

## 8.2： ##

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NTA0MjU2OQ_size_16_color_FFFFFF_t_70 6][]

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NTA0MjU2OQ_size_16_color_FFFFFF_t_70 7][]

**jsp****文件：****page**

![2020072213555574.png][]  
局部代码块：  
        可以将java代码跟页面展示的标签写到一个jsp页面中，java代码转译成的servlet（程序）文件中，java代码跟输出是保存在service（服务）方法中  
        缺点：  
            代码可读性比较差，开发比较麻烦

=====================================================================  
![2020072213555588.png][]

![20200722135555102.png][]

idea中显示：![20200722135555100.png][]

全局代码块：java文件中：![20200722135555112.png][] 
        定义公共的方法的时候需要使用全局代码块使用<%!%>，生成的代码在servlet类中 
        调用的时候需要使用局部代码块

=====================================================================

### **1****、（输出变量）** ###

![20200722135633531.png][] ** **

输出结果也可用：<% =a %>方式输出

比如：

<% String i =“jsp简单”;%>

<% =i %>

页面显示：![20200722135633531.png][]

### **2****、（输出整个方法）** ###

![20200722135633531.png][]

![20200722135633529.png][]

=====================================================================

//contentType:表示浏览器解析响应信息的时候使用的编码和解析格式

//language：表示jsp要转译成的文件类型

//导入java.util.\* 和java.lang.\* 的包![20200722135633541.png][]

//pageEncoding="utf-8" 是设置页面编码格式（改英文）

<%@ page contentType="text/html;charset=UTF-8" language="java" import="java.util.*,java.lang.*" pageEncoding="utf-8" %>
 
 //turn：保留session对象
 //false：不保留session对象
 
 <%@ page session="true" %>

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NTA0MjU2OQ_size_16_color_FFFFFF_t_70 8][]![20200722135818318.png][]

**创建jsp文件：****error.jsp**

**添加：**

![20200722135827512.png][] ![20200722135831571.png][]

![20200722135835695.png][]**（发生逻辑错误）**

//errorPage:当页面发生逻辑错误的时候，跳转指定页面
 <%@ page errorPage="error.jsp" isErrorPage="true" %>
 
 //继承，要继承的父类（包名+类名）
 <%@ page errorPage="error.jsp" extends="？？" %>
 
 <%
 String path = request.getContextPath();
 System.out.println(path);
 
 String basePath = request.getScheme()
 +"://"
 +request.getServerName()
 +":"
 +request.getServerPort()
 +path
 +"/";
 System.out.println(basePath);
 %>

页面导入的方式![20200722135915843.png][]  
        静态导入：  
            不会将静态导入的页面生成一个新的servlet文件，而是将两个文件合并  
            优点：运行效率高  
            缺点：两个页面会耦合到一起，两个页面中不能存在相同名称的变量，不利于维护  
        动态导入：  
            两个页面不会进行合并，分别生成自己的servlet文件，但是页面在最终展示的时候是合并到一起的  
            优点：没有耦合，可以存在同名的变量  
**//**jsp文件：staticImport（静态导入）![20200722135936704.png][]

<%@ **include** file="staticImport.jsp"%>

**//**jsp文件：dynamicImport（动态导入）![2020072213595925.png][] 
<**jsp****:****include** page="dynamicImport.jsp"></**jsp****:****include**>

**创建：jsp文件：****staticImport****（静态导入）**![20200722140012786.png][]

**调试：（该文件与主文件）**

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
 <html>
 <head>
 <title>Title</title> //网页名称
 </head>
 <body>
 <%
 //int i= 200; //另一个文件不能有变量i（不能重名，会500）
 %>
 我是静态导入页面
 </body>
 </html>

**创建：jsp文件：****dynamicImport（动态导入）**![20200722140040248.png][]

**调试：（该文件与主文件）**

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
 <html>
 <head>
 <title>Title</title> //网页名称
 </head>
 <body>
 我是动态导入
 </body>
 </html>

**请求转发：**（登录进去时，转发到另一个地址（程序））

![20200722140114373.png][]

**jsp****文件：****page**

**添加：**

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NTA0MjU2OQ_size_16_color_FFFFFF_t_70 9][]

**jsp****文件：****forward****（请求转发）**

**添加：**

<body>![2020072214022027.png][] （地址没变） 
我是转发页面 
</body>

**jsp****文件：****page**

**添加：**

![20200722140237731.png][]

**jsp****文件：****forward****（请求转发）**

**添加：**

<%=request.getParameter("china")%>
 <hr> //横线
 <%=request.getParameter("hebei")%>

![20200722140324814.png][]

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NTA0MjU2OQ_size_16_color_FFFFFF_t_70]: /images/20230209/bdf0d620858c45edb6a34529cb7695ef.png
[20200722134436537.png]: https://img-blog.csdnimg.cn/20200722134436537.png
[20200722134439236.png]: /images/20230209/673e790a8b6849dcab4da4f9771a9b68.png
[20200722134506611.png]: https://img-blog.csdnimg.cn/20200722134506611.png
[2020072213450967.png]: /images/20230209/f79b9980f5074652b507da50c6545295.png
[20200722134528352.png]: https://img-blog.csdnimg.cn/20200722134528352.png
[20200722134534140.png]: /images/20230209/4940f5c9e9cc469aaf45bb94614f9a00.png
[20200722134602149.png]: https://img-blog.csdnimg.cn/20200722134602149.png
[20200722134613707.png]: /images/20230209/b6aa5b4369a04e53a6ed24178663dbc2.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NTA0MjU2OQ_size_16_color_FFFFFF_t_70 1]: /images/20230209/222e46ed34cf4771ae4bd1b956de22de.png
[20200722134718115.png]: https://img-blog.csdnimg.cn/20200722134718115.png
[20200722134721870.png]: /images/20230209/873c5438c8eb4700876754a40453da95.png
[2020072213480581.png]: https://img-blog.csdnimg.cn/2020072213480581.png
[20200722134808900.png]: /images/20230209/3bf2cf6afd464b5da3d5f91f99dd5410.png
[20200722134815313.png]: https://img-blog.csdnimg.cn/20200722134815313.png
[20200722134817936.png]: /images/20230209/f337c5eed0a242d3ad64b4d1e7a39cec.png
[20200722134836470.png]: https://img-blog.csdnimg.cn/20200722134836470.png
[20200722134839205.png]: /images/20230209/ecf589fed0bb402480ca36e4032ce30f.png
[2020072213491639.png]: https://img-blog.csdnimg.cn/2020072213491639.png
[20200722134918979.png]: /images/20230209/f73ce67582fa4c40a5829541730572cf.png
[20200722134957793.png]: /images/20230209/3dab148cc9cc455091108c787bf711f6.png
[2020072213501236.png]: https://img-blog.csdnimg.cn/2020072213501236.png
[20200722135014665.png]: /images/20230209/673fc5984022441088958b8d12d0b074.png
[20200722135042566.png]: https://img-blog.csdnimg.cn/20200722135042566.png
[20200722135045207.png]: /images/20230209/626820b8cfeb4fed9d429d99255adf36.png
[20200722135127308.png]: https://img-blog.csdnimg.cn/20200722135127308.png
[20200722135130729.png]: /images/20230209/4a83d99cd46646448c9cd9d4fb4ef298.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NTA0MjU2OQ_size_16_color_FFFFFF_t_70 2]: /images/20230209/c1a1cc1bca284ee8b4d206e61a93cd13.png
[20200722135238813.png]: /images/20230209/637824a71ca942ef8515084294ecee4c.png
[20200722135332462.png]: /images/20230209/4253859914bd445096664f4ecbdbe354.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NTA0MjU2OQ_size_16_color_FFFFFF_t_70 3]: /images/20230209/f78e18e46ab24e9db535e650f72c0edd.png
[20200722135442904.png]: https://img-blog.csdnimg.cn/20200722135442904.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NTA0MjU2OQ_size_16_color_FFFFFF_t_70 4]: /images/20230209/273b67fca8504809a7235e6d661a59fa.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NTA0MjU2OQ_size_16_color_FFFFFF_t_70 5]: /images/20230209/226c06d6bc5c479d879bcec936907edd.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NTA0MjU2OQ_size_16_color_FFFFFF_t_70 6]: /images/20230209/1f9e8f7be82b4b9294820099bbec5d02.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NTA0MjU2OQ_size_16_color_FFFFFF_t_70 7]: /images/20230209/55d46449807c49a28aa8b24da87aa053.png
[2020072213555574.png]: /images/20230209/9cb38576c74b4b3e9fd7579ca9c9061b.png
[2020072213555588.png]: /images/20230209/87e2d4156d4b4f729c707a1de13b864b.png
[20200722135555102.png]: /images/20230209/5632174632214271bb4d90f3e60e6e2b.png
[20200722135555100.png]: /images/20230209/d796f09b670d489e95b3283d5252bfc6.png
[20200722135555112.png]: /images/20230209/eb29859e92d34feb8665b5c844fbbb06.png
[20200722135633531.png]: /images/20230209/e87a72b25b974144bad3a8ba31dad279.png
[20200722135633529.png]: /images/20230209/6518f42b85864166a8fdf6db274fe995.png
[20200722135633541.png]: /images/20230209/cd45ae3c66ba456db7f0bc9927c7219d.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NTA0MjU2OQ_size_16_color_FFFFFF_t_70 8]: https://img-blog.csdnimg.cn/20200722135811493.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NTA0MjU2OQ==,size_16,color_FFFFFF,t_70
[20200722135818318.png]: /images/20230209/885d118bf24a445ca19ca83f8ec9305a.png
[20200722135827512.png]: https://img-blog.csdnimg.cn/20200722135827512.png
[20200722135831571.png]: /images/20230209/5e31376774fa41eab3caaf0836719d0e.png
[20200722135835695.png]: /images/20230209/7eec13d1c5ee4d47b319c3cffa1e955c.png
[20200722135915843.png]: /images/20230209/5a2b569d9f9a4a8588c56d8574e2cb1b.png
[20200722135936704.png]: /images/20230209/a8feed9064dc446e82c35de71a9a87f0.png
[2020072213595925.png]: /images/20230209/a37e8fdbe92740ab841a02ebcb0d5f69.png
[20200722140012786.png]: /images/20230209/a4e5f2e23f2e4756ab231695a2448166.png
[20200722140040248.png]: /images/20230209/3e1e0b5636a04524a836449c43541335.png
[20200722140114373.png]: /images/20230209/58522e2cf902464c82af83569718efe9.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NTA0MjU2OQ_size_16_color_FFFFFF_t_70 9]: /images/20230209/d2e9d1b3a82945bf9171615d7f5487bb.png
[2020072214022027.png]: /images/20230209/99bf14bcb9ce4e25b38cfe67ffaaa651.png
[20200722140237731.png]: /images/20230209/4bae3ccaf12d41fcbc6694fd6e8c734c.png
[20200722140324814.png]: /images/20230209/a8b1f60fb5534fce98f62b2021d2ba6d.png