学习笔记——JSP入门知识点

一、学习重点

二、学习内容

案例一

查询学生（以表格形式）
遍历集合并显示在页面上，table表格展示
1.在JSP脚本片段中只能写java
2.在body中只能写html

<%@ page import="com.jsoft.entity.Student" %>
<%@ page import="java.util.List" %>
<%@ page pageEncoding="utf-8" contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
welcome:<%= request.getAttribute("username")%>
<%
    List<Student> students = (List<Student>)   request.getAttribute("students");
%>
<table border="1" cellpadding="10" cellspacing="0">
    <tr>
        <th>ID</th>
        <th>NAME</th>
        <th>AGE</th>
        <th>GENDER</th>
    </tr>
    <%
        for (Student student : students) {
    %>

        <tr>
            <td><%= student.getId()%></td>
            <td><%= student.getName()%></td>
            <td><%= student.getAge()%></td>
            <td><%= student.getGender()%></td>
        </tr>
    <%
        }
    %>

</table>
</body>
</html>

案例二

登录，如果登录成功，跳转到某个jsp页面，并且显示登录的用户名
欢迎你：xxx
admin

登录成功，欢迎你：admin

思路：输入账号和密码在servlet中比对，比对成功，把用户名放进作用域。

作用域对象的使用规则：
从小到大使用！！！------- request！！！

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
</head>
<body>
</body>
</html>

package com.jsoft2;

import com.jsoft.entity.Student;

import javax.servlet.*;
import javax.servlet.http.*;
import javax.servlet.annotation.*;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.List;
import java.util.Objects;

@WebServlet(name = "LoginJspServlet", value = "/loginjsp.do")
public class LoginJspServlet extends HttpServlet {

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        request.setCharacterEncoding("utf-8");

        String username = request.getParameter("username");
        String password = request.getParameter("password");

        PrintWriter out = response.getWriter();

        List<Student> students = new ArrayList<>(5);
        students.add(new Student(1001,"aaa",25,"Man"));
        students.add(new Student(1002,"bbb",26,"Man"));
        students.add(new Student(1003,"ccc",28,"Man"));
        students.add(new Student(1004,"ddd",27,"Man"));
        students.add(new Student(1005,"eee",24,"Man"));

        if(Objects.equals(username,"admin") && Objects.equals(password,"123456")){
            request.setAttribute("username",username);
            request.setAttribute("students",students);
            request.getRequestDispatcher("jsp/welcome.jsp").forward(request,response);
        }else {
            out.write("username or password wrong");
        }
    }
}

案例三

分页查询：
1、总记录数
2、总页数
3、每页显示的记录数
4、每页展示的数据集合
5、导航栏的页码 【1,2,3,4,5】
6、是否是第一页
7、是否是最后一页
8、当前页

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<html>
<head>
    <title>Title</title>
</head>
<body>
<h1><a href="${pageContext.request.contextPath}/page.do?pagenum=1">加载分页导航</a></h1>
当前页：【${requestScope.pagenum}】，总页数【${requestScope.pageCount}】
<hr>
<c:if test="${requestScope.pagenum ne 1}">
    <a href="${pageContext.request.contextPath}/page.do?pagenum=1">首页</a>
    <a href="${pageContext.request.contextPath}/page.do?pagenum=${requestScope.pagenum - 1}">上一页</a>
</c:if>
<c:if test="${requestScope.pagenum eq 1}">
    <span>首页</span>
    <span>上一页</span>
</c:if>
<c:forEach begin="1" end="${requestScope.pageCount}" var="i">
    <c:if test="${requestScope.pagenum eq i}">
        <span>${i}</span>
    </c:if>
    <c:if test="${requestScope.pagenum ne i}">
        <a href="${pageContext.request.contextPath}/page.do?pagenum=${i}">${i}</a>
    </c:if>
</c:forEach>
<c:if test="${requestScope.pagenum ne requestScope.pageCount}">
    <a href="${pageContext.request.contextPath}/page.do?pagenum=${requestScope.pagenum + 1}">下一页</a>
    <a href="${pageContext.request.contextPath}/page.do?pagenum=${requestScope.pageCount}">尾页</a>
</c:if>
</body>
</html>


package com.jsoft2;

import javax.servlet.*;
import javax.servlet.http.*;
import javax.servlet.annotation.*;
import java.io.IOException;
import java.util.Objects;

@WebServlet(name = "PageServlet", value = "/page.do")
public class PageServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String pagenumStr = request.getParameter("pagenum");
        Integer pagenum = 1;
        Integer pageCount = 20;
        try{

            if(Objects.nonNull(pagenumStr)){
                pagenum = Integer.parseInt(pagenumStr);
            }

            if(pagenum <= 0){
                pagenum = 1;
            }

            if(pagenum > 20){
                pagenum = 20;
            }

        } catch (Exception e){
            pagenum = 1;
        }


        request.setAttribute("pagenum",pagenum);
        request.setAttribute("pageCount",pageCount);

        request.getRequestDispatcher("jsp/page.jsp").forward(request,response);
    }
}

三、笔记内容

JSP

JSP脚本片段：用于在JSP页面写java代码

面试题：JSP和servlet的区别？
1、JSP本质上就是一个servlet
2、JSP更侧重于视图展示，servlet更侧重于逻辑处理
3、先有的servlet，后有的JSP

注意：
1、JSP脚本片段中只能出现java代码，不能出现HTML元素。在访问JSP时，JSP引擎翻译JSP页面中的脚本片段。
2、JSP脚本片段中的java代码必须严格遵守java的规则
3、一个JSP页面是可以有多个脚本片段
4、多个脚本片段中的代码可以相互访问

<%
    int num = 0;
    num++;
//    System.out.println(num);

%>
<%
    System.out.println(num);
    // 向页面打印输出
    out.print(num);
%>

JSP表达式

<%= num %>

JSP声明片段

<%!
    int x = 10;

    static{

    }

    public void fun(){

    }
%>

JSP的指令标识

  • <%@ 指令名 属性1="值1" 属性2="值2" .....%>
  • page指令：定义整个JSP页面的相关属性
  • include指令：引入其他的JSP页面。先把两个页面结合，在去编译成servlet。
  • taglib指令：引入页面上需要用到的标签库
<%@ page import="java.util.List" %>
<%@ page import="java.util.ArrayList" %>
<%@ page errorPage="error.jsp" contentType="text/html;charset=UTF-8" language="java" %>
<%@include file="hello.jsp"%>
<html>
<head>
    <title>Title</title>
</head>
<body>
<%
    List list = new ArrayList();
//    int i = 10 / 0;
%>
<h1>JSP02 Page!!!</h1>
</body>
</html>

<%@ page isErrorPage="true" contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
</head>
<body>
    <h1>Error Page!!!</h1>
    <%=
        exception.getMessage()
    %>
</body>
</html>

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
</head>
<body>
    <h1>hello Page!!!</h1>
</body>
</html>

JSP标签
1、内置标签
（1）jsp:include：引入指定的页面
（2）jsp:forward：转发页面
（3）jsp:param：传参数
2、JSTL标签，需要导入JSTL标签库
3、自定义标签

面试题：jsp:include标签和include指令的区别？
include标签：先把要引入的页面编译，再合并
include指令：先把要引入的页面合并，再编译

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
</head>
<body>
<h1>JSP03 Page!!!</h1>
<jsp:include page="hello.jsp"></jsp:include>
<jsp:forward page="hello.jsp">
    <jsp:param name="num1" value="10"/>
    <jsp:param name="num2" value="20"/>
</jsp:forward>
</body>
</html>

JSP四大作用域：
1、当前页（pageContext）:一个属性只能在一个页面中获取。
2、一次请求（request）：一个页面中设置的属性，范围是一次请求。
3、一次会话（session）：一个会话中的属性，只要页面不关闭，都能获取到
4、整个web应用（application）：在这个服务器上，当前项目下的任何一个位置都能获取。

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
</head>
<body>

<%
    pageContext.setAttribute("pageContext","pageContext");
    request.setAttribute("request","request");
    session.setAttribute("session","session");
    application.setAttribute("application","application");
%>

<h1>pageContext：<%= pageContext.getAttribute("pageContext")%></h1>
<h1>request：<%= request.getAttribute("request")%></h1>
<h1>session：<%= session.getAttribute("session")%></h1>
<h1>application：<%= application.getAttribute("application")%></h1>

<jsp:forward page="jsp04_copy.jsp"></jsp:forward>

</body>
</html>

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
</head>
<body>

<h1>jsp04_copy page</h1>

<h1>pageContext：<%= pageContext.getAttribute("pageContext")%></h1>
<h1>request：<%= request.getAttribute("request")%></h1>
<h1>session：<%= session.getAttribute("session")%></h1>
<h1>application：<%= application.getAttribute("application")%></h1>

</body>
</html>

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
</head>
<body>

<h1>jsp05</h1>

<h1>pageContext：<%= pageContext.getAttribute("pageContext")%></h1>
<h1>request：<%= request.getAttribute("request")%></h1>
<h1>session：<%= session.getAttribute("session")%></h1>
<h1>application：<%= application.getAttribute("application")%></h1>

</body>
</html>

package com.jsoft.servlet;

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.jsp.PageContext;
import java.io.IOException;

@WebServlet("/jsp.do")
public class JSPServlet extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        /*
            pageContext--PageContext
            request------HttpServletRequest
            session------HttpSession
            application--ServletContext
         */
        System.out.println(req.getAttribute("request"));
        System.out.println(req.getSession().getAttribute("session"));
        System.out.println(req.getServletContext().getAttribute("application"));
    }
}

面试题：JSP的九大内置对象。内置：不需要创建，直接就能用。

对象名 作用
request 请求
response 响应
session* 会话
out 输出
page 当前JSP页面对象
application 应用
exception* 异常，只能在指定了isErrorPage="true"
pageContext 当前页，作用域
config 配置 
<%@ page session="false" isErrorPage="true" contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
</head>
<body>

<%
    out.print("<h1>out对象</h1>");
%>

</body>
</html>

EL表达式
EL表达式的内置作用域对象

pageContext
requestScope
sessionScope
applicationScope

EL表达式的缺陷：1、只能读，不能写 2、不支持流程控制语句

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
</head>
<body>

    <%
        request.setAttribute("name","zhangsan");
        session.setAttribute("name","lisi");
        pageContext.setAttribute("age",30);
    %>

<%--    <input type="text" value="<%= request.getAttribute("name1") == null ? "" : request.getAttribute("name1")%>">--%>
    <input type="text" value="${sessionScope.name}">
    <hr>
    ${age eq 1}
    <hr>
    取参数：${param.username},${paramValues.hobby},${initParam.password}

</body>
</html>


<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<html>
<head>
    <title>Title</title>
</head>
<body>
    <%--  向指定的作用域中设置值  --%>
    <c:set scope="session" var="name" value="zhangsan"></c:set>
    <c:set scope="session" var="age" value="20"></c:set>
    ${sessionScope.name}

    <hr>
    <c:if test="${sessionScope.age >= 18}">成年！</c:if>
    <c:if test="${sessionScope.age < 18}">未成年！</c:if>

    <hr>
    <c:choose>
        <c:when test="${sessionScope.age eq 18}">
            你已经年满18岁，可以签署劳动合同了！
        </c:when>
        <c:when test="${sessionScope.age lt 18}">
            你好没有满18岁！
        </c:when>
        <c:otherwise>
            你已经是大人了！！！
        </c:otherwise>
    </c:choose>
    <hr>
    <c:forEach begin="1" end="10" step="2" var="i" varStatus="stat">
        ${i} ----- ${stat.first} <br>
    </c:forEach>

</body>
</html>

WebInfServlet

package com.jsoft2;

import javax.servlet.*;
import javax.servlet.http.*;
import javax.servlet.annotation.*;
import java.io.IOException;

@WebServlet(name = "WebInfServlet", value = "/WebInfServlet")
public class WebInfServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//        request.getRequestDispatcher("/WEB-INF/aaa.jsp").forward(request,response);
        response.sendRedirect("WEB-INF/aaa.jsp");
    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

    }
}
posted @   LJMMJL  阅读(47)  评论(0)  编辑  收藏  举报
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