Java Day16 Servlet(二)

Servlet

1、继承结构
2、ServletConfig对象
3 、ServletContext
- 3.1 获得路径
- 3.2 域对象相关API
4、HttpServletRequest
- 4.1 获得请求行和请求头相关api
- 4.2 请求中键值对相关api

1、继承结构

顶级Servlet接口

//初始化
 void init(ServletConfig var1) throws ServletException;
//得到配置内容 ServletConfig对象
    ServletConfig getServletConfig();
//处理用户请求的方法
    void service(ServletRequest var1, ServletResponse var2) throws ServletException, IOException;
//返回Servlet字符串描述信息的方法
    String getServletInfo();
//销毁方法
    void destroy();

GenericServlet 抽象类一些实现的方法

   private transient ServletConfig config;
   //返回配置类对象
     public ServletConfig getServletConfig() {
        return this.config;
    }
    //初始化 可以将配置信息添加到当前实例中，实例化时 初始化使用的是该函数
 public void init(ServletConfig config) throws ServletException {
        this.config = config;
        this.init();//调用无参的init方法
    }
//我们要初始化的是无参的init方法，这样可以不用管config对象，也可以定义自己需要实现的init方法
    public void init() throws ServletException {
    }

HttpServlet 抽象类

//实现了service方法，将Servlet对象强转为HttpServlet对象。
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(lStrings.getString("http.non_http"));
        }

        this.service(request, response);
    }

如果我们继承了Httpserlet 可以重写service方法，也可以重写doget或者dopost等方法。

2、ServletConfig对象

为Servlet提供初始配置参数的一种对象,每个Servet都有自己独立唯一的Servletconfig对象。容器会为每个Servlet实例化一个Servletconfig对象,并通过Servlet生命周期的init方法传入给serviet作为属性。

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="https://jakarta.ee/xml/ns/jakartaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="https://jakarta.ee/xml/ns/jakartaee https://jakarta.ee/xml/ns/jakartaee/web-app_5_0.xsd"
         version="5.0">
    <servlet>
        <servlet-name>userServlet</servlet-name>
        <servlet-class>com.cky.servlet.UserServlet</servlet-class>
        <init-param>
            <param-name>kaya</param-name>
            <param-value>valuea</param-value>
        </init-param>
        <init-param>
            <param-name>kayb</param-name>
            <param-value>valueb</param-value>
        </init-param>
    </servlet>
    <servlet-mapping>
        <servlet-name>userServlet</servlet-name>
        <url-pattern>/userservlet</url-pattern>
    </servlet-mapping>
</web-app>

package com.cky.servlet;

import jakarta.servlet.ServletConfig;
import jakarta.servlet.ServletException;
import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;

import java.io.IOException;
import java.io.PrintWriter;
import java.util.Enumeration;

//配置多个url路径 使用value 是一样饿效果
//@WebServlet(urlPatterns ={"/s1","/s2"})
public class UserServlet extends HttpServlet {
    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        ServletConfig servletConfig=this.getServletConfig();
        Enumeration<String> initParameterNames = servletConfig.getInitParameterNames();
        while(initParameterNames.hasMoreElements()){
            String s = initParameterNames.nextElement();
            System.out.println(s); //kaya
                                   // kayb
        }
    }
}

注解方式

package com.cky.servlet;

import jakarta.servlet.ServletConfig;
import jakarta.servlet.ServletContext;
import jakarta.servlet.ServletException;
import jakarta.servlet.annotation.WebInitParam;
import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;

import java.io.IOException;
import java.io.PrintWriter;
import java.util.Enumeration;

//配置多个url路径 使用value 是一样饿效果
@WebServlet(urlPatterns ={"/s1","/s2"},
        initParams = {@WebInitParam(name ="kaya",value = "vlauea"),
        @WebInitParam(name="keyb",value = "vb")})
public class UserServlet extends HttpServlet {
    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        ServletConfig servletConfig=getServletConfig();
        Enumeration<String> initParameterNames = servletConfig.getInitParameterNames();
        while (initParameterNames.hasMoreElements()){
            String s = initParameterNames.nextElement();
            String initParameter = servletConfig.getInitParameter(s);
            System.out.println(s+"--->"+initParameter);//keyb--->vb
                                                        //kaya--->vlauea
        }
    }
    }

3 、ServletContext

Servletcontext对象有称呼为上下文对象,或者叫应用域对象(后面统一讲解域对象)。容器会为每个app创建一个独立的唯-的Servletcontext对象
。ServletContext对象为所有的Servlet所共享
ServletContext可以为所有的Servlet提供初始配置参数
在这里插入图片描述

package com.cky.servlet;

import jakarta.servlet.ServletConfig;
import jakarta.servlet.ServletContext;
import jakarta.servlet.ServletException;
import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;

import java.io.IOException;
import java.io.PrintWriter;
import java.util.Enumeration;

//配置多个url路径 使用value 是一样饿效果
//@WebServlet(urlPatterns ={"/s1","/s2"})
public class UserServlet extends HttpServlet {
    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //ServletContext servletContext=this.getServletContext();
        ServletContext servletContext=getServletContext();

        Enumeration<String> initParameterNames = servletContext.getInitParameterNames();
        while(initParameterNames.hasMoreElements()){
            String s = initParameterNames.nextElement();
            String initParameter = servletContext.getInitParameter(s);
            System.out.println(s+"-->"+initParameter); //code-->i
        }
    }
}

    <context-param>
        <param-name>code</param-name>
        <param-value>i</param-value>
    </context-param>

3.1 获得路径

package com.cky.servlet;

import jakarta.servlet.ServletConfig;
import jakarta.servlet.ServletContext;
import jakarta.servlet.ServletException;
import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;

import java.io.IOException;
import java.io.PrintWriter;
import java.util.Enumeration;

//配置多个url路径 使用value 是一样饿效果
//@WebServlet(urlPatterns ={"/s1","/s2"})
public class UserServlet extends HttpServlet {
    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //ServletContext servletContext=this.getServletContext();
        ServletContext servletContext=getServletContext();
      //获得文件的部署路径  在磁盘中目录位置
        String upload = servletContext.getRealPath("upload");// E:\java_code\web_all\out\artifacts\web02_war_exploded\upload
        System.out.println(upload);
        //获得项目的上下文路径 / 访问路径
        String contextPath = servletContext.getContextPath();
        System.out.println(contextPath); // web02
    }
    }

在这里插入图片描述

3.2 域对象相关API

ServletContext 是最大的一个域对象，应用中所有的Servlet共享域对象中的内容。
在这里插入图片描述

package com.cky.servlet;

import jakarta.servlet.ServletConfig;
import jakarta.servlet.ServletContext;
import jakarta.servlet.ServletException;
import jakarta.servlet.annotation.WebInitParam;
import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;

import java.io.IOException;
import java.io.PrintWriter;
import java.util.Enumeration;

//配置多个url路径 使用value 是一样饿效果
@WebServlet(urlPatterns ={"/s1","/s2"},
        initParams = {@WebInitParam(name ="kaya",value = "vlauea"),
        @WebInitParam(name="keyb",value = "vb")})
public class UserServlet extends HttpServlet {
    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        ServletContext servletContext=getServletContext();
        servletContext.setAttribute("ka",2);

    }
    }

package com.cky.servlet;

import jakarta.servlet.ServletContext;
import jakarta.servlet.ServletException;
import jakarta.servlet.annotation.WebInitParam;
import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;

import java.io.IOException;

@WebServlet(urlPatterns ={"/s3",})
public class UserServlet1  extends HttpServlet {
    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        ServletContext servletContext=getServletContext();
        int ka = (int)servletContext.getAttribute("ka");
        System.out.println(ka);  //2
    }
}

先运行UserServlet 设置值，之后运行UserServlet1获得属性值，如果先执行UserServlet1，会获得null。

4、HttpServletRequest

4.1 获得请求行和请求头相关api

package com.cky.servlet;

import jakarta.servlet.ServletConfig;
import jakarta.servlet.ServletContext;
import jakarta.servlet.ServletException;
import jakarta.servlet.annotation.WebInitParam;
import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;

import java.io.IOException;
import java.io.PrintWriter;
import java.util.Enumeration;

//配置多个url路径 使用value 是一样饿效果
@WebServlet(urlPatterns ={"/s1","/s2"},
        initParams = {@WebInitParam(name ="kaya",value = "vlauea"),
        @WebInitParam(name="keyb",value = "vb")})
public class UserServlet extends HttpServlet {
    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //行相关 Get/POST URI HTTP/1.1
        System.out.println(req.getMethod());//请求方式 GET
        System.out.println(req.getScheme());//请求协议 http
        System.out.println(req.getProtocol());//请求协议和版本 HTTP/1.1
        System.out.println(req.getRequestURI());//资源标识符 /web02/s1
        System.out.println(req.getRequestURL());//资源定位符 http://localhost:8081/web02/s1
        System.out.println(req.getLocalPort());//本应用容器端口号  8081
        System.out.println(req.getServerPort()); //客户端发请求的端口号 与上一个可能不同，因为中间可能经过代理 8081
        System.out.println(req.getRemotePort()); //客户端软件端口号 53389

        //头相关
        System.out.println(req.getHeader("Accept")); //获取单个 text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.7
        //获得所有
        Enumeration<String> headerNames = req.getHeaderNames(); 
        while (headerNames.hasMoreElements()) {
            String s = headerNames.nextElement();
            System.out.println(s+":"+req.getHeader(s));
        }


    }
    }

4.2 请求中键值对相关api

http://localhost:8081/web02/s1?username=cky&passward=123&hobby=篮球&hobby=sing

package com.cky.servlet;

import jakarta.servlet.ServletConfig;
import jakarta.servlet.ServletContext;
import jakarta.servlet.ServletException;
import jakarta.servlet.annotation.WebInitParam;
import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;

import java.io.IOException;
import java.io.PrintWriter;
import java.util.Arrays;
import java.util.Enumeration;
import java.util.Map;
import java.util.Set;

//配置多个url路径 使用value 是一样饿效果
@WebServlet(urlPatterns ={"/s1","/s2"},
        initParams = {@WebInitParam(name ="kaya",value = "vlauea"),
        @WebInitParam(name="keyb",value = "vb")})
public class UserServlet extends HttpServlet {
    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //获取单个参数
        String username = req.getParameter("username");  //cky
        System.out.println(username);
        //获取多个值
        String[] hobbies = req.getParameterValues("hobby");
        System.out.println(Arrays.toString(hobbies)); // [篮球, sing]

        //获取所有参数名
        Enumeration<String> parameterNames = req.getParameterNames();
        while (parameterNames.hasMoreElements()) {
            String pname = parameterNames.nextElement();
            String[] parameterValues = req.getParameterValues(pname);
            if(parameterValues.length>1){
                System.out.println(Arrays.toString(parameterValues));
            }
            else
                System.out.println(parameterValues[0]);
        }
//        cky
//        123
//        [篮球, sing]

        //获得参数的 Map集合
        Map<String, String[]> parameterMap = req.getParameterMap();
        Set<Map.Entry<String, String[]>> entries = parameterMap.entrySet();
        for (Map.Entry<String, String[]> entry : entries) {
            String key = entry.getKey();
            String[] parameterValues = req.getParameterValues(key);
            if (parameterValues.length > 1) {
                System.out.println(Arrays.toString(parameterValues));
            } else
                System.out.println(parameterValues[0]);

        }
        //        cky
//        123
//        [篮球, sing]

    }
    }