Web项目基础(2) – neet`s Blog

# servlet2

## 1.servlet是否线程安全 (线程特性)

“`
线程安全的指标
//1.是否有共享数据
//2.多线程对共享数据做写操作
“`

servlet中不要创建成员变量

“`java
servlet是单实例的所以成员变量(不加static) 就会在多线程间共享
如果service()方法中对成员变量有写操作则线程不安全
servlet中非特殊情况不要加锁 (直接降级为单线程效率大大降低)
“`

## 2.servlet中提供的域对象

javaEE j2EE java企业级应用 (web应用程序)

核心对象servlet servlet中还包含其他的对象还有隐含的对象

域对象是servlet中隐含的对象

##### 域对象是空的map (在程序运行时共享数据使用)

通用的api

“`java
域对象.setAttribute("key",value);
域对象.getAttribute("key")
“`

##### 域的生效时机和失效时机

“`java
1请求域 request域
“`

![image-20241120100116402](http://43.155.216.63:21080/wp-content/uploads/2025/12/image-20241120100116402.png

request读+写

“`java
package com.javasm.controller;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

/**
* @author gfs
* @version 0.1
* @className RequestDemo1
* @descriptioin:
* @date 2024/11/20 10:37
* @since jdk11
*/
@WebServlet("/requestDemo1")
public class RequestDemo1 extends HttpServlet {

@Override
protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//request域 service方法中的第一个参数 req
req.setAttribute("reqKey","reqVal");

//读取对象的格式读到之后强转为实际类型
String reqKey =(String) req.getAttribute("reqKey");

System.out.println("demo1中读取:"+reqKey);
//调用指定路径servlet的service方法
req.getRequestDispatcher("requestDemo2").forward(req,resp);

}
}

“`

request 只读取

“`java
package com.javasm.controller;

/**
* @author gfs
* @version 0.1
* @className RequestDemo1
* @descriptioin:
* @date 2024/11/20 10:37
* @since jdk11
*/
@WebServlet("/requestDemo2")
public class RequestDemo2 extends HttpServlet {

@Override
protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//request域 service方法中的第一个参数 req
//req.setAttribute("reqKey","reqVal");

//读取对象的格式读到之后强转为实际类型
String reqKey =(String) req.getAttribute("reqKey");

System.out.println("demo2中读取:"+reqKey);

}
}

“`

“`java
2会话域 session域
可以在多次请求间生效
对不同的浏览器进程数据分开存储
“`

![image-20241120100850350](http://43.155.216.63:21080/wp-content/uploads/2025/12/image-20241120100850350.png

session读+写

“`java
package com.javasm.controller;

/**
* @author gfs
* @version 0.1
* @className RequestDemo1
* @descriptioin:
* @date 2024/11/20 10:37
* @since jdk11
*/
@WebServlet("/sessionDemo1")
public class SessionDemo1 extends HttpServlet {

@Override
protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//session域多次请求间共享数据使用
//如果需要使用session对象需要通过代码主动触发
HttpSession session = req.getSession();

session.setAttribute("sesKey","sesVal");

String sesKey =(String) session.getAttribute("sesKey");

System.out.println("demo1中读取:"+sesKey);

}
}

“`

session只读取

“`java
package com.javasm.controller;

/**
* @author gfs
* @version 0.1
* @className RequestDemo1
* @descriptioin:
* @date 2024/11/20 10:37
* @since jdk11
*/
@WebServlet("/sessionDemo2")
public class SessionDemo2 extends HttpServlet {

String sesKey =(String) session.getAttribute("sesKey");

System.out.println("demo2中读取:"+sesKey);

}
}

“`

“`java
3服务器域 servletContext域
全局共享写入之后所有请求所有浏览器都可以使用
“`

![image-20241120101141506](http://43.155.216.63:21080/wp-content/uploads/2025/12/image-20241120101141506.png

servletContext读+写

“`java
package com.javasm.controller;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.io.IOException;

/**
* @author gfs
* @version 0.1
* @className RequestDemo1
* @descriptioin:
* @date 2024/11/20 10:37
* @since jdk11
*/
@WebServlet("/ServletContextDemo1")
public class ServletContextDemo1 extends HttpServlet {

@Override
protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//ServletContext 服务器对象

ServletContext servletContext = req.getServletContext();
//ServletContext servletContext1 = this.getServletContext();

servletContext.setAttribute("sckey","scval");
String sckey =(String) servletContext.getAttribute("sckey");
System.out.println("demo1中读取:"+sckey);

}
}

“`

servletContext只读取

“`java
package com.javasm.controller;

/**
* @author gfs
* @version 0.1
* @className RequestDemo1
* @descriptioin:
* @date 2024/11/20 10:37
* @since jdk11
*/
@WebServlet("/ServletContextDemo2")
public class ServletContextDemo2 extends HttpServlet {

@Override
protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//ServletContext 服务器对象

ServletContext servletContext = req.getServletContext();
//ServletContext servletContext1 = this.getServletContext();

String sckey =(String) servletContext.getAttribute("sckey");
System.out.println("demo2中读取:"+sckey);

}
}

“`

## 3servlet中常用对象

#### 3.1servletContext对象

servletContext对象也叫application 是服务器对象

这是一个全局共享的对象一般用来存放和共享服务器级别的全局参数

###### 常用方法:

“`java
* getContextPath() 获取服务入口路径 /day10 方便拼路径使用
* getRealPath("/") 获取服务器实际代码路径做本地IO操作时使用
* getInitParameter("charset") 通过web.xml 读取自定义公共参数
“`

###### 示例代码:

“`java
package com.javasm.controller2;

@WebServlet("/scDemo")
public class ServletContextDemo extends HttpServlet {
@Override
protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//servletContext对象 application 服务器对象
//全局共享的对象全局数据
/*
* getContextPath() 获取服务入口路径 /day10 方便拼路径使用
* getRealPath("/") 获取服务器实际代码路径做本地IO操作时使用
* getInitParameter("charset") 通过web.xml 读取自定义公共参数
* */
// 获取服务入口路径 /day10 方便拼路径使用
ServletContext servletContext = req.getServletContext();
System.out.println(servletContext.getContextPath());

// 获取服务器实际代码路径
//D:\develop\workspace\two\day10_servlet2\target
// \day10_servlet2-1.0-SNAPSHOT\ 做本地IO操作时使用
System.out.println(servletContext.getRealPath("/"));

//通过web.xml 读取自定义公共参数
String initParameter = servletContext.getInitParameter("charset");
System.out.println(initParameter);
}
}

“`

#### 3.2servletConfig对象(了解)

servlet配置参数对象可以获取servlet名称等配置参数现在的开发中基本用不到

#### 3.3request对象(***)

HttpServletRequest 请求对象

两个作用:

“`
1.解析请求报文包含请求报文中的各种参数
2.做request域对象
“`

###### 常用方法:

“`java
//域对象设置键值对
req.setAttribute("reqKey","reqVal");
//域对象读取键值对注意要强转类型
String reqKey =(String) req.getAttribute("reqKey");
“`

“`java
//指定字符编码处理post请求时的请求乱码
req.setCharacterEncoding("utf-8");
//取请求参数
String 参数值 = req.getParameter("参数key");
//取请求同key参数 ?hobby=1&hobby=2&hobby=3 取出字符串数组
String[] hobbies = req.getParameterValues("hobby");
“`

“`java
获取参数map 获取参数输入流 (了解)
//tomcat解析参数时会把键值对存入map
//单个参数也会存入数组
Map parameterMap = req.getParameterMap();

//tomcat中允许自己读取请求体中的数据可以自己解析数据
//获得请求体部分的输入流
ServletInputStream inputStream = req.getInputStream();
“`

“`java
获取请求头 (了解)
//自定义请求头取自定义请求头(需搭配ajax使用)
String headerKey = req.getHeader(“headerKey”);
“`

“`java
获取请求报文中的各种路径
//获取报文中路径中的数据
//获取协议
System.out.println(req.getScheme());
//获取主机名
System.out.println(req.getServerName());
//获取端口
System.out.println(req.getServerPort());
//获取服务器入口的根路径
System.out.println(req.getContextPath());
//URL 与 URI
//URL 统一资源定位符 http://localhost:8080/day10/reqDemo
System.out.println(req.getRequestURL());
//URI 统一资源标识符 /day10/reqDemo
System.out.println(req.getRequestURI());
//servlet配置的路径匹配路径 /reqDemo
System.out.println(req.getServletPath());
“`

“`java
请求转发
可以在servlet之间跳转先执行servlet1 —> servlet2

//请求转发同一次请求访问多个servlet时使用可以让请求跳转
//请求跳转时配合request域做数据共享提供机制一般搭配jsp使用
req.getRequestDispatcher(“servlet2的路径”).forward(req,resp);
“`

###### 示例代码:

“`java
package com.javasm.controller2;

import javax.servlet.ServletException;
import javax.servlet.ServletInputStream;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.Map;

/**
* @author gfs
* @version 0.1
* @className RequestDemo
* @descriptioin:
* @date 2024/11/20 11:11
* @since jdk11
*/
@WebServlet(“/reqDemo”)
public class RequestDemo extends HttpServlet {
@Override
protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//req HttpServletRequest
//1.解析请求报文包含请求报文中的各种参数
//2.做request域对象
/*
//域对象设置键值对
req.setAttribute(“reqKey”,”reqVal”);
//域对象读取键值对注意要强转类型
String reqKey =(String) req.getAttribute(“reqKey”);

//取参数相关
//指定字符编码处理post请求时的请求乱码
req.setCharacterEncoding(“utf-8”);
//取请求参数
String 参数值 = req.getParameter(“参数key”);
//取请求同key参数 ?hobby=1&hobby=2&hobby=3 取出字符串数组
String[] hobbies = req.getParameterValues(“hobby”);

//tomcat解析参数时会把键值对存入map
//单个参数也会存入数组
Map parameterMap = req.getParameterMap();

//tomcat中允许自己读取请求体中的数据可以自己解析数据
//获得请求体部分的输入流
ServletInputStream inputStream = req.getInputStream();

//自定义请求头取自定义请求头
String headerKey = req.getHeader(“headerKey”);

*
*
* */
// //tomcat解析参数时会把键值对存入map
// //单个参数也会存入数组
// Map parameterMap = req.getParameterMap();
// System.out.println(parameterMap.get(“name”)[0]);

/* 获取参数的请求体输入流
可以自己解析请求体数据配合其他工具也可以直接解析为对象
与tomcat解析流数据互斥流只能读一次
ServletInputStream inputStream = req.getInputStream();
BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream));
String s = bufferedReader.readLine();
System.out.println(s);

String username = req.getParameter(“username”);
System.out.println(username);
*
*
* */
//读请求报文只能读请求体可以读post方式的请求体
//字符
//字节
//流只能读一次
ServletInputStream inputStream = req.getInputStream();

BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream));
String s = bufferedReader.readLine();
System.out.println(s);

String username = req.getParameter(“username”);
System.out.println(username);
//获取报文中路径中的数据
//获取协议
System.out.println(req.getScheme());
//获取主机名
System.out.println(req.getServerName());
//获取端口
System.out.println(req.getServerPort());
//获取服务器入口的根路径
System.out.println(req.getContextPath());
//URL 与 URI
System.out.println(req.getRequestURL());//URL 统一资源定位符 http://localhost:8080/day10/reqDemo
System.out.println(req.getRequestURI());//URI 统一资源标识符 /day10/reqDemo
//servlet配置的路径匹配路径 /reqDemo
System.out.println(req.getServletPath());
//请求转发同一次请求访问多个servlet时使用可以让请求跳转
//请求跳转时配合request域做数据共享提供机制一般搭配jsp使用
// req.getRequestDispatcher(“地址”).forward(req,resp);

}
}

“`

#### 3.4response对象(***)

HttpServletResponse 响应对象控制响应报文相关的内容

###### 常用方法

“`java
//设置返回数据格式
//resp.setContentType(“application/json;charset=utf-8”); //返json
//resp.setContentType(“text/html;charset=utf-8”); //返页面标签
resp.setContentType(“text/html;charset=utf-8”);

//获得输出流
//动态网页技术数据是否动态生成
PrintWriter writer = resp.getWriter();
writer.print(“这是一个动态页面
“);
writer.print(““);
// writer.write();
// writer.println();

“`

###### 示例代码

“`java
package com.javasm.controller2;

/**
* @author gfs
* @version 0.1
* @className ResponseDemo
* @descriptioin:
* @date 2024/11/20 14:32
* @since jdk11
*/
@WebServlet(“/respDemo”)
public class ResponseDemo extends HttpServlet {
@Override
protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
System.out.println(“触发运行了….”);
//返回页面标签
//设置返回数据格式
//resp.setContentType(“application/json;charset=utf-8”);
//resp.setContentType(“text/html;charset=utf-8”);
resp.setContentType(“text/html;charset=utf-8”);
//获得输出流
//动态网页技术数据是否动态生成
PrintWriter writer = resp.getWriter();
writer.print(“这是一个动态页面
“);
writer.print(“");
// writer.write();
// writer.println();
writer.close();
}
}

“`

#### 3.5session对象(***)

HttpSession 会话对象做域对象(缓存数据) 在同一个用户(浏览器)多次访问间共享数据

###### 常用方法

“`java
//域对象设置键值对
req.setAttribute("sesKey","sesVal");
//域对象读取键值对注意要强转类型
String reqKey =(String) req.getAttribute("sesKey");
//删除键值对
req.removeAttribute("sesKey");
“`

“`java
//获得session编号用来检查是否同一个session对象
session.getId()
//设置session访问间隔单位秒超过间隔会重新创建session
session.setMaxInactiveInterval(5);
//直接设置session失效
session.invalidate();
“`

###### 示例代码

“`java
package com.javasm.controller2;

/**
* @author gfs
* @version 0.1
* @className HttpSessionDemo
* @descriptioin:
* @date 2024/11/20 14:40
* @since jdk11
*/
@WebServlet("/sesDemo")
public class HttpSessionDemo extends HttpServlet {
@Override
protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

//获得session对象 req.getSession()
HttpSession session = req.getSession();
//session编号 C03DDD56DF31BAB3EB6A41DB728815CF
//每个session都会起编号如过session对象相同编号是相同的
System.out.println(session.getId());
//MaxInactiveInterval 最大非活动周期两次访问的间隔
//
//session.setMaxInactiveInterval(5);
session.invalidate();
/*
* session三种失效方式
* 1.浏览器关闭
* 2.超过访问间隔
* 3.直接设置session失效
*
* */
//session对象保留但是sesison中的数据可以清除掉
//session.removeAttribute("key");

/*
* session使用场景
* 1.当缓存使用把一些常用的数据存入session 服务端需要使用时直接使用共享的数据
* 2.做访问控制
* 登录访问控制
*
* */

}
}

“`

###### session常用场景

“`java
* session使用场景
* 1.当缓存使用把一些常用的数据存入session 服务端需要使用时直接使用共享的数据
* 2.做访问控制
* 登录访问控制
“`

登录访问控制场景:

![image-20241120152954172](http://43.155.216.63:21080/wp-content/uploads/2025/12/image-20241120152954172.png

###### 示例代码

登录服务 LoginServlet

“`java
package com.javasm.controller3;

/**
* @author gfs
* @version 0.1
* @className LoginServlet
* @descriptioin:
* @date 2024/11/20 15:03
* @since jdk11
*/
@WebServlet("/login")
public class LoginServlet extends HttpServlet {
@Override
protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//做登录….
System.out.println("登录代码执行了……");

HttpSession session = req.getSession();
session.setAttribute("loginUser","用户信息….");

}
}

“`

用户服务 UserServlet

“`java
package com.javasm.controller3;

/**
* @author gfs
* @version 0.1
* @className LoginServlet
* @descriptioin:
* @date 2024/11/20 15:03
* @since jdk11
*/
@WebServlet("/user")
public class UserServlet extends HttpServlet {
@Override
protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//查用户信息必须登录后使用

HttpSession session = req.getSession();
String loginUser =(String) session.getAttribute("loginUser");
if(loginUser!=null){
System.out.println("查询用户代码执行了……");
}else{
System.out.println("请先登录……");
}

}
}

“`

商品服务 ProdServlet

“`java
package com.javasm.controller3;

/**
* @author gfs
* @version 0.1
* @className LoginServlet
* @descriptioin:
* @date 2024/11/20 15:03
* @since jdk11
*/
@WebServlet("/prod")
public class ProdServlet extends HttpServlet {
@Override
protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//查商品信息不需要登录
System.out.println("查询商品代码执行了……");

}
}

“`

登出服务 LogoutServlet

“`java
package com.javasm.controller3;

/**
* @author gfs
* @version 0.1
* @className LoginServlet
* @descriptioin:
* @date 2024/11/20 15:03
* @since jdk11
*/
@WebServlet("/logout")
public class LogoutServlet extends HttpServlet {
@Override
protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//做登出….
System.out.println("登出代码执行了……");

HttpSession session = req.getSession();
//session.setAttribute("loginUser","用户信息….");
//session.invalidate();
session.removeAttribute("loginUser");
}
}

“`

![image-20241120154126511](http://43.155.216.63:21080/wp-content/uploads/2025/12/image-20241120154126511.png

![image-20241120171518464](http://43.155.216.63:21080/wp-content/uploads/2025/12/image-20241120171518464.png

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