Java j2ee JSTL 无法打印对象列表答案

【问题标题】：Java j2ee JSTL cannot print a list of objectsJava j2ee JSTL 无法打印对象列表
【发布时间】：2015-03-28 21:44:40
【问题描述】：

我目前正在从事一个小型 Java J2E 项目。

我想在 *.jsp 页面中打印一个对象列表，但是有一个我似乎无法摆脱的错误。

我的 .jsp 页面：

<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
    <title>Cars</title>
    <link type="text/css" rel="stylesheet" href="Styles/style.css" />
</head>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<%@ include file="/WEB-INF/header.html" %>
<%@ include file="/WEB-INF/Menus/menu-logged_in.jsp" %>
<%@ page import="java.util.List" %>
<%@ page import="com.SupTracking.beans.Car" %>

<body>
    <h1>Cars</h1>
    <p>
        You currently have <c:out value="${requestScope.nbcar }"></c:out> car(s) registered.<br/>
        <a href="/SupTracking/cars/newcar">Register a new car</a>
    </p>

    <c:if test="${requestScope.cars != null }">
    <h2>Car List :</h2>
    <ul>
        <c:forEach items="${requestScope.cars}" var="element"> 
            <li>${element.Name }</li>
        </c:forEach>
    </ul>
    </c:if>
</body>
</html>

当我尝试用${element} 替换${element.Name} 时，我得到beans.Car@3a7488b4，所以我确实得到了我的对象，只是无法探索它。

我的班级：

public class Car {
private int CarID;
private int UserID;
private String Name;
private String Brand;
private int DateRegistration;
private Float CarLatitude;
private Float CarLongitude;
private Timestamp CarTimestamp;

//Getters and Setters
public void SetCarID(int id) {this.CarID = id;}
public int GetCarID() {return this.CarID;}

public void SetUserID(int id) {this.UserID = id;}
public int GetUserID() {return this.UserID;}

public void SetName(String n) {this.Name = n;}
public String GetName() {return this.Name;}

public void SetBrand(String b) {this.Brand = b;}
public String GetBrand() {return this.Brand;}

public void SetDateRegistration(int d) {this.DateRegistration = d;}
public int GetDateRegistration() {return this.DateRegistration;}

public void SetCarLatitude(Float lat) {this.CarLatitude = lat;}
public Float GetCarLatitude() {return this.CarLatitude;}

public void SetCarLongitude(Float lon) {this.CarLongitude = lon;}
public Float GetCarLongitude() {return this.CarLongitude;}

public void SetCarTimeStamp (Timestamp t) {this.CarTimestamp = t;}
public Timestamp GetCarTimestamp() {return this.CarTimestamp;}
}

最后，错误堆栈：

【问题讨论】：

考虑更改字段名称和方法以遵循 bean 约定，因此它们应该以小写开头，例如 CarID -> carID。 SetCarID->setCarID....
哎呀，我的错，我在写这篇文章的时候已经改变了。也就是说，即使使用 getName()，错误仍然存在
我刚刚用这些更改测试了你的代码，它似乎解决了你的问题。

标签： java jsp jakarta-ee jstl

【解决方案1】：

根据 Java 命名约定，字段和方法的名称应为驼峰式

private String name;

public String getName(){ return name; }
public void setName(String name){ this.name=name; }

JavaBeans 也遵循此约定，因此将字段和名称的首字母更改为小写。

哦，更改后不要忘记更新您的 EL 查询以使用 ${element.name}，而不是 ${element.Name}

通过这些更改，以下示例对我来说效果很好：

Car.javaJavaBean

package whatever;

public class Car {
    private String name;
    private String brand;

    // Getters and Setters
    public void setName(String n) {
        this.name = n;
    }

    public String getName() {
        return this.name;
    }

    public void setBrand(String b) {
        this.brand = b;
    }

    public String getBrand() {
        return this.brand;
    }

    public Car(String name, String brand) {
        this.name = name;
        this.brand = brand;
    }

    @Override
    public String toString() {
        return "Car [Name=" + name + ", Brand=" + brand + "]";
    }

}

CarTestservlet

@WebServlet("/CarTest")
public class CarTest extends HttpServlet {
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        List<Car> list = new ArrayList<Car>();
        list.add(new Car("car1", "brand1"));
        list.add(new Car("car2", "brand2"));
        list.add(new Car("car3", "brand3"));
        list.add(new Car("car4", "brand4"));
        request.setAttribute("cars", list);
        request.getRequestDispatcher("/index.jsp").forward(request, response);
    }
}

index.jsp查看

<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
    <title>Cars</title>
    <link type="text/css" rel="stylesheet" href="Styles/style.css" />
</head>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<%@ page import="java.util.List" %>

<body>
    <h2>Car List :</h2>
    <ul>
        <c:forEach items="${requestScope.cars}" var="element"> 
            <li>${element.name }</li>
        </c:forEach>
    </ul>
</body>
</html>

【讨论】：