认识达内从这里开始

昆明达内的老师给大家讲JSTL标签出错：<c:forEach var="book" items="${requestScope.books}" varStatus="status">

昆明达内的老师发现同学在JSTL标签代码的时候出错，总结一下：

问题1.The JSP specification requires that an attribute name is preceded by whitespace

解决：<c:forEach var="book" items="${requestScope.books}"varStatus="status">出错

改为：<c:forEach var="book" items="${requestScope.books}" varStatus="status">

原因：varStatus="status"前加空格

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问题2.Property 'isbn' ot found on type java.lang.String

解决：<c:forEach var="book" items=" ${requestScope.books}" varStatus="status">出错

改为：<c:forEach var="book" items="${requestScope.books}" varStatus="status">

原因：${requestScope.books}前去掉空格

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问题3.程序能运行了,jsp能访问，但是EL表达式读取不到想要的信息  

解决：没有在.xml配置文件添加servlet的<url-pattern>信息，无法调用servlet向jsp传对象。

在.xml文件中添加：

<servlet>

<servlet-name>BooksServlet</servlet-name>

<servlet-class>com.controller.BooksServlet</servlet-class>

</servlet>

<servlet-mapping>

<servlet-name>BooksServlet</servlet-name>

<url-pattern>/BooksServlet</url-pattern>

</servlet-mapping>

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jstl标签练习代码：

1.BooksServlet.java

1 package com.controller;

2 import java.io.IOException;

3 import javax.servlet.RequestDispatcher;

4 import javax.servlet.ServletException;

5 import javax.servlet.annotation.WebServlet;

6 import javax.servlet.http.HttpServlet;

7 import javax.servlet.http.HttpServletRequest;

8 import javax.servlet.http.HttpServletResponse;

9 import java.util.List;

10 import java.util.ArrayList;

11 import com.model.Book;

12 //@WebServlet("/BooksServlet")

13 public class BooksServlet extends HttpServlet {

14    @Override

15    public void doGet(HttpServletRequest request, HttpServletResponse response)

16    throws ServletException, IOException {

17       List<Book> books = new ArrayList<Book>();

18       Book book1 = new Book("978-7-302-23059-5","Java语言程序设计",45.00);

19       Book book2 = new Book("978-7-302-21540-0","Java Web编程技术",39.00);

20       Book book3 = new Book("978-7-302-24130-0","C #入门经典",99.80);

21       books.add(book1);

22       books.add(book2);

23       books.add(book3);

24       request.setAttribute("books", books);

25       RequestDispatcher rd = request.getRequestDispatcher("/books.jsp");

26       rd.forward(request, response);

27      }

28 }

2.Book.java（javaBean类）

1 package com.model;

2

3 public class Book {

4   private String isbn;

5   private String title;

6   private double price;

7   public Book(String isbn, String title, double price) {

8    super();

9    this.isbn = isbn;

10    this.title = title;

11    this.price = price;

12    }

13    public String getIsbn() {

14        return isbn;

15    }

16    public void setIsbn(String isbn) {

17        this.isbn = isbn;

18    }

19    public String getTitle() {

20        return title;

21    }

22    public void setTitle(String title) {

23        this.title = title;

24    }

25    public double getPrice() {

26        return price;

27    }

28    public void setPrice(double price) {

29        this.price = price;

30    }

31        

32   

33 }

3.books.jsp

1 package com.model;

2

3 public class Book {

4   private String isbn;

5   private String title;

6   private double price;

7   public Book(String isbn, String title, double price) {

8    super();

9    this.isbn = isbn;

10    this.title = title;

11    this.price = price;

12    }

13    public String getIsbn() {

14        return isbn;

15    }

16    public void setIsbn(String isbn) {

17        this.isbn = isbn;

18    }

19    public String getTitle() {

20        return title;

21    }

22    public void setTitle(String title) {

23        this.title = title;

24    }

25    public double getPrice() {

26        return price;

27    }

28    public void setPrice(double price) {

29        this.price = price;

30    }

31        

32   

33 }

4.配置文件.xm

1 <?xml version="1.0" encoding="UTF-8"?>

2 <web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="#/xml/ns/javaee" xsi:schemaLocation="#/xml/ns/javaee #/xml/ns/javaee/web-app_2_5.xsd" id="WebApp_ID" version="2.5">

3  <display-name>Ex_JSTL_tag</display-name>

4  <servlet>

5    <servlet-name>BooksServlet</servlet-name>

6    <servlet-class>com.controller.BooksServlet</servlet-class>

7  </servlet>

8  <servlet-mapping>

9    <servlet-name>BooksServlet</servlet-name>

10    <url-pattern>/BooksServlet</url-pattern>

11  </servlet-mapping>

12  <welcome-file-list>

13    <welcome-file>index.html</welcome-file>

14    <welcome-file>index.htm</welcome-file>

15    <welcome-file>books.jsp</welcome-file>

16    <welcome-file>default.htm</welcome-file>

17    <welcome-file>default.jsp</welcome-file>

18  </welcome-file-list>

19 </web-app>

5.运行时注意加入  http://localhost/Ex_JSTL_tag/BooksServlet

只有在url中加入/BooksServlet才能调用到servlet想jsp传参数

昆明达内的老师后面还会给同学们讲其他容易错误的地方。