java web学习

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1.HTTP响应包含三部分：请求行，请求头，请求体。具体结构如图所示

2.状态码

3.contextType的作用是浏览器采用何种方式对响应体进行处理

4.请求转发和重定向：

多个servlet中的跳转有两种方式：

第一种：request.getRequestDispatcher().forward();//请求转发它是在服务器，即tomcat内部，把请求从第一个servlet转发到第二个servlet.。请求转发是服务器跳转，只会产生一次请求。

第二种:response.sendRedirect；//响应重定向从浏览器重新发送一个新的请求给servlet，会产生两次请求

设置请求自定义属性值：设置请求属性：request.setAttribute(属性名，属性值)

获取属性值：request.getAttribute（属性名）；

5.浏览器cookie:cookie是浏览器保存在本地的文本内容，常用来保存用户登录状态，用户资料等小文本.cookie具有时效性，cookie内容会伴随请求发送给tomcat

package com.xiaoqiang.servlet;

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

/**
 * Servlet implementation class FirstServlet
 */
@WebServlet("/Test")
public class FirstServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;
       
    /**
     * @see HttpServlet#HttpServlet()
     */
    public FirstServlet() {
        super();
        // TODO Auto-generated constructor stub
    }

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    /*    String output="<h1 style='color:red'>"+"小强</h1>";
        response.setContentType("text/xml;charset=utf-8");
        response.getWriter().println(output);*/
    
        /*response.sendRedirect("/servlet_study/Test_1");*/
        Cookie cookie=new Cookie("user", "xiaoqiang");
        response.addCookie(cookie);
        request.setAttribute("xiaoqiang", "小强");
        request.getRequestDispatcher("/Test_1").forward(request, response);
        
        
    }

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    /*protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        doGet(request, response);
    }*/

}

cookies的创建

//获取cookie中的所有值
//伪代码
Cookie [] cookies=request.getCookies();

for(Cookie coo:cookies)

6.session:session（用户会话）用于保存与“浏览器窗口”对应的数据，session的数据存储在tomcat服务器的内存中，具有时效性。session通过

浏览器cookie的sessionId值提取用户数据。

session传递的小例子：

package com.xiaoqiang.servlet;

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

/**
 * Servlet implementation class FirstServlet
 */
@WebServlet("/Test")
public class FirstServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;
       
    /**
     * @see HttpServlet#HttpServlet()
     */
    public FirstServlet() {
        super();
        // TODO Auto-generated constructor stub
    }

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    /*    String output="<h1 style='color:red'>"+"小强</h1>";
        response.setContentType("text/xml;charset=utf-8");
        response.getWriter().println(output);*/
    
        /*response.sendRedirect("/servlet_study/Test_1");*/
      /*  Cookie cookie=new Cookie("user", "xiaoqiang");
        response.addCookie(cookie);*/
        HttpSession session=request.getSession();
        session.setAttribute("xiaoqiang", "小强123");
    /*    request.setAttribute("xiaoqiang", "小强");*/
        request.getRequestDispatcher("/Test_1").forward(request, response);
        
        
    }

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    /*protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        doGet(request, response);
    }*/

}

package com.xiaoqiang.servlet;

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

/**
 * Servlet implementation class SecondServlet
 */
@WebServlet("/Test_1")
public class SecondServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;
       
    /**
     * @see HttpServlet#HttpServlet()
     */
    public SecondServlet() {
        super();
        // TODO Auto-generated constructor stub
    }

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        String output="<h1 style='color:red'>"+request.getSession().getAttribute("xiaoqiang")+"</h1>";
        response.setContentType("text/html;charset=utf-8");
        response.getWriter().println(output);
    }

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    /*protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        doGet(request, response);
    }*/

}

7.servletContext:ServletContext(Servlet上下文对象),是web应用全局变量，一个web应用只会创建一个ServletContext对象，

一个ServletContext随着web应用启动而创建

//伪代码
ServletContext servletcontext=request.getServletContext();
servletcontext.setAuttribute(K,V);

8.java web 三大作用域对象：HttpServletRequest 请求对象 HttpSession 用户会话对象 ServletContext web应用全局对象

它们的作用域和生命周期是依次递增的。

9.解决post请求中的中文乱码：由于tomcat的默认使用字符集ISO-8859-1，属于西欧字符集

解决字符集乱码的核心是把字符集iso-8859-1转化为UTF-8，servlet中请求与响应都需要设置UTF-8。

可以用request.setCharacterEncoding("UTF-8") 方法用于将请求体中的文字字符集转换为UTF-8。

对于tomcat8.x版本以上的get发送中文请求默认是utf-8的格式，无需转换。

response响应也要设置utf-8的编码

10.web.xml中常用配置

在web.xml中写入标签全局变量参数 <context-parm><parm-name>名称</parm-name><parm-value>值</parm-value> </context-parm>

错误跳转<error-page><error-code>错误编码</error-code><location>路径</locathion></error-page>

11.jsp中的九大内置对象

1.request 请求对象 HttpServletRequest

2.response 响应对象 HttpServletRespone

3.session 用户会话 HttpSession

4.application 应用全局变量 ServletContext

5.out 输出对象 PrintWrite

6.page 当前页面对象 this

7.pageContext 页面上下文对象 PageContext

8.config 应用配置对象 ServletConfig

9.exception 应用异常对象 Throwable