接笔记15.
1、不管是JSP中的<%%>还是<%=%>最终都将处于servlet的方法体中，那么有没有一种元素可以声明成类的成员呢？
——答案是有，而且非常非常简单，这个元素就是<%!%>，我们用它来解决笔记15中的问题，只需要在原基础上加一个感叹号就可以了。
<%@ page import="Sample.Counter" %> <%@ page contentType="text/html;charset=UTF-8" language="java" %> <html> <head> <title>Basic Counter</title> </head> <body> <%! int count = 0; %> <p>The page count is: </p> <%= ++count %> </body> </html>
2、我们还可以在感叹号里添加类的成员方法。
JSP隐式对象（内置对象）
1、out并不是唯一的JSP内置对象！
什么是JSP内置对象呢？本质上来说，所有的JSP内置对象最终都将映射为Servlet/JSP API中的某个东西。
例如，内置对象request实质上就是service的参数HttpServletRequest的一个映射。
2、课本练习
index.html
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <title></title> </head> <body> <form action="HobbyPage.do" method="post"> <p>choose a hobby:</p> <select name="hobby" id="" size="1"> <option value="看书">看书</option> <option value="打王者荣耀">打王者荣耀</option> <option value="写代码">写代码</option> <option value="水群">水群</option> </select> <br /> <input type="submit"> </form> </body> </html>
web.xml
<?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_3_1.xsd" version="3.1"> <servlet> <servlet-name>hi</servlet-name> <servlet-class>Sample.AddFriends</servlet-class> </servlet> <servlet-mapping> <servlet-name>hi</servlet-name> <url-pattern>/HobbyPage.do</url-pattern> </servlet-mapping> </web-app>
AddFriends.java
package Sample; import javax.servlet.RequestDispatcher; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import java.io.IOException; import java.util.ArrayList; import java.util.List; public class AddFriends extends HttpServlet { @Override protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { req.setCharacterEncoding("utf-8"); List names = new ArrayList(); names.add("Fred"); names.add("Pradeep"); names.add("Philippe"); req.setAttribute("names", names); RequestDispatcher view = req.getRequestDispatcher("result.jsp"); view.forward(req, resp); } }
result.jsp
<%@ page import="java.util.List" %> <%@ page import="java.util.Iterator" %><%-- Created by IntelliJ IDEA. User: xkfx Date: 2017/6/14 Time: 17:27 To change this template use File | Settings | File Templates. --%> <%@ page contentType="text/html;charset=UTF-8" language="java" %> <html> <head> <title>Title</title> </head> <body> <% // response.setCharacterEncoding("utf-8"); %> <p>hello i'm result</p> <p>The friends who share your hobby <%=request.getParameter("hobby")%> is :</p> <% List names = (List) request.getAttribute("names"); Iterator it = names.iterator(); while(it.hasNext()) { out.println(it.next() + "<br />"); } %> </body> </html>
写这道题碰到的两个极端坑爹的地方：
- html中，submit的参数是value而不是文本！更详细可以参考这里：Java Web开发之Servlet获取表单值
- 要想最终得到的html显示中文，既不是在AddFriends.java中 resp.setCharacterEncoding("utf-8");也不是在result.jsp中 response.setCharacterEncoding("utf-8"); 而是在AddFriends.java中 req.setCharacterEncoding("utf-8");