2-2-3 Java Web基础-Servlet与JSP

HTTP请求结构

包含三部分:请求行,请求头,请求体

 

 

使用userAgent开发多端应用

userAgent请求头可以获取操作环境,可以做多端开发

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;

/**
 * @description: 利用请求头开发多端应用
 */
@WebServlet("/ua")
public class UserAgentServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String userAgent = request.getHeader("User-Agent");
        response.setContentType("text/html;charset=utf-8");
        String output = "";
        response.getWriter().println(userAgent);
        if (userAgent.indexOf("Windows NT") != -1) {
            output = "<h1>这是PC端首页</h1>";
        } else if(userAgent.indexOf("iPhone") != -1 || userAgent.indexOf("Android") != -1) {
            output= "<h1>这是移动端首页</h1>";
        }
        response.getWriter().println(output);
    }
}

HTTP响应结构

包含三部分:响应行,响应头,响应头

 

 HTTP常见状态码

状态码	描述
200	服务器处理成功
404	无法找到文件
500	内部服务器错误
403	服务器拒绝访问
301,302	请求重定向
400	无效的请求
401	未经过授权
503	服务器超负载或正停机维护,无法处理请求

ContentType的作用

ContType决定浏览器采用何种方式对响应体进行处理

MINE类型	描述
text/plain	纯文本
text/html	HTML文档
text/xml	XML文档
application/x-msdownload	需要下载的资源
image/jpeg image/gif image/...	图片资源

 

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;

@WebServlet("/ct")
public class ContentTypeServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String output = "<h1><a href='http://www.baidu.com'><span>百度</span></a></h1>";
        response.setContentType("text/html;charset=utf-8");
        response.getWriter().println(output);
    }
}

请求转发与响应重定向

多个servlet(jsp)之间跳转有两种方式

request.getRequestDispatcher().forward()-请求转发

请求转发是服务器跳转,只会产生一次请求,且浏览器网页地址不会发生改变

response.sendRedirect()-响应重定向

响应重定向是浏览器跳转,会产生两次请求,浏览器网页地址会发生改变

设置请求自定义属性

设置请求属性:request.setAttribute(属性名,属性值)

获取请求属性:request.getAttribute(属性名)

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;


@WebServlet("/direct/checkLogin")
public class CheckLoginServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("用户登录成功");
        request.setAttribute("username","admin");
        //请求转发
        //request.getRequestDispatcher("/direct/index").forward(request,response);
        //响应重定向需要增加contextPath
        response.sendRedirect("/servletAndJsp/direct/index");
    }
}

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;


@WebServlet("/direct/index")
public class IndexServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String username = (String)request.getAttribute("username");
        response.getWriter().println("This is index page!current username is " + username);
    }
}

注意使用响应重定向不会获取到跳转的请求属性,因为响应重定向会产生两次请求,第二次请求获取不到第一请求的属性.

浏览器Cookie

Cookie是浏览器保存在本地的文本内容

Cookie常用于保存登录状态,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

Cookie使用方法

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 java.io.IOException;


@WebServlet("/cookie/login")
public class CookieLoginServlet extends HttpServlet {

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        System.out.println("用户登录成功");
        Cookie cookie = new Cookie("user", "admin");
        cookie.setMaxAge(60 * 60 * 24 *7);
        response.addCookie(cookie);
        response.getWriter().println("login success");
    }
}

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 java.io.IOException;


@WebServlet("/cookie/index")
public class CookieIndexServlet extends HttpServlet {

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //request.getCookies()用户获取所有的Cookie
        Cookie[] cs = request.getCookies();
        if(cs == null) {
            response.getWriter().println("user not login");
            return;
        }
        String user = null;
        for(Cookie c : cs) {
            System.out.println(c.getName() + ":" + c.getValue());
            if(c.getName().equals("user")) {
                user = c.getValue();
                break;
            }
        }

        if(user == null) {
            response.getWriter().println("user not login");
        }else {
            response.getWriter().println("user:" + user);
        }

    }
}

 Session-用户会话

Session(用户会话)用于保存于"浏览器窗口"对应的数据

Session的数据存储在Tomcat服务器内存中,具有时效性

Session通过浏览器Cookie的SessionId值提取用户数据

Session常用方法

request.getSession() - 获取Session对象

get|set|removeAttribute() -获取|设置|删除Session对象

setMaxInactiveInterval - 设置Session超时时间

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;


@WebServlet("/session/login")
public class SessionLoginServlet extends HttpServlet {

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("用户登录成功");
        HttpSession session = request.getSession();
        String sessionId = session.getId();
        System.out.println(sessionId);
        session.setAttribute("name", "张三");
        request.getRequestDispatcher("/session/index").forward(request, response);

    }
}

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;


@WebServlet("/session/index")
public class SessionIndexServlet extends HttpServlet {

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        HttpSession session = request.getSession();
        String sessionId = session.getId();
        System.out.println(sessionId);
        String name = (String)session.getAttribute("name");
        response.setContentType("text/html;charset=utf-8");
        response.getWriter().println("这是首页，当前用户为:" + name);
    }
}

ServletContext

ServletContext(Servlet上下文对象),是web应用全局对象

一个Web应用只会创建一个ServletContext对象

ServletContext随着Web应用启动而自动创建.

在web.xml文件中添加

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
         version="4.0">

    <context-param>
        <param-name>copyright</param-name>
        <param-value>© 2018 mingm.com</param-value>
    </context-param>
    <context-param>
        <param-name>title</param-name>
        <param-value>初始化数据</param-value>
    </context-param>
</web-app>

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 java.io.IOException;

@WebServlet("/servletcontext/init")
public class ServletContextInitServlet extends HttpServlet {

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        ServletContext context = request.getServletContext();
        String copyright = context.getInitParameter("copyright");
        context.setAttribute("copyright", copyright);
        String title = context.getInitParameter("title");
        context.setAttribute("title", title);
        response.getWriter().println("init success");
    }
}

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 java.io.IOException;

@WebServlet("/servletcontext/default")
public class ServletContextDefaultServlet extends HttpServlet {

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        ServletContext context = (ServletContext)request.getServletContext();
        String copyright = (String)context.getAttribute("copyright");
        String title = (String)context.getAttribute("title");
        response.setContentType("text/html;charset=utf-8");
        response.getWriter().println("<h1>" + title + "</h1>" + copyright);
    }
}

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

作用范围依次扩大

Web应用的中文乱码

原因

Tomcat默认使用字符集ISO-8859-1,属于西欧字符集

解决乱码的核心思路是将ISO-8859-1转化为UTF-8

Servlet中请求与响应都需要设置UTF-8字符集

解决方法

请求乱码解决

方法一:

String ename = request.getParameter("ename");
String address = request.getParameter("address");
System.out.println(ename + ":" + address);
String utf8Ename = new String(ename.getBytes("iso-8859-1") , "utf-8");
String utf8Address = new String(address.getBytes("iso-8859-1") , "utf-8");

方法二:在doPost方法中使用

//request.setCharacterEncoding方法用于将请求体中的字符集转换为UTF-8
request.setCharacterEncoding("UTF-8");

方法三:修改Tomcat配置

进入/apache-tomcat-8.5.51/conf/server.xml文件

找到

    <Connector port="8080" protocol="HTTP/1.1"
               connectionTimeout="20000"
               redirectPort="8443" />

添加URIEncoding="UTF-8"

    <Connector port="8080" protocol="HTTP/1.1"
               connectionTimeout="20000"
               redirectPort="8443" URIEncoding="UTF-8" />

注意:对于Tomcat8.x的版本，默认get请求发送中文就是UTF-8的格式，因此无需转换

响应乱码解决

response.setContentType("text/html;charset=utf-8");

web.xml配置

默认页面

  <welcome-file-list>
    <welcome-file>index.html</welcome-file>
    <welcome-file>index.htm</welcome-file>
    <welcome-file>index.jsp</welcome-file>
    <welcome-file>default.html</welcome-file>
    <welcome-file>default.htm</welcome-file>
    <welcome-file>default.jsp</welcome-file>
  </welcome-file-list>

利用url传参

  <servlet>
      <servlet-name>patternServlet</servlet-name>
      <servlet-class>com.imooc.servlet.pattern.PatternServlet</servlet-class>
  </servlet>
  <servlet-mapping>
      <servlet-name>patternServlet</servlet-name>
      <url-pattern>/pattern/*</url-pattern>
  </servlet-mapping>

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class PatternServlet extends HttpServlet{

    @Override
    protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //查询员工的基本信息
        //获取当前访问的URL
        String url = request.getRequestURL().toString();
        System.out.println(url);
        String id = url.substring(url.lastIndexOf("/") + 1);
        int eid =  Integer.parseInt(id);
        response.setContentType("text/html;charset=utf-8");
        PrintWriter out = response.getWriter();
        out.println(id);
        if(eid == 1) {
            out.println("张三");
        }else if(eid == 2) {
            out.println("李四");
        }else {
            out.println("其他员工");
        }
        
    }
    
}

访问路径为:localhost:8080/context_path/pattern/1

设置404,500等状态码默认页面

  <!-- 指定错误页面 -->
  <error-page>
      <error-code>404</error-code>
      <location>/error/404.html</location>
  </error-page>
  <error-page>
      <error-code>500</error-code>
      <location>/error/500.jsp</location>
  </error-page>

JSP九大内置对象

内置对象	描述
request	请求对象 - HttpServletRequest
response	响应对象 - HttpServletResponse
session	用户会话 -HttpSession
application	应用全局对象 - ServletContext
out	输出对象 - PrintWriter
page	当前页面对象 - this
pageContext	页面上下文对象 - PageContext
config	应用配置对象 - ServletConfig
exception	应用异常对象 - Throwable