Spring MVC应用程序将库存添加到购物车jsp JAVA

Question

我正在尝试编写简单的网络应用程序，其中包含一些可以添加到购物车的库存。我将复制代码和jsp文件。我希望我能解决这个问题。我从数据库中获取数据。现在我想显示添加到购物车的内容，稍后我将尝试将其保存在数据库中。

完整堆栈跟踪。

    org.apache.jasper.JasperException: An exception occurred processing JSP page /WEB-INF/views/cart.jsp at line 14

11:     <div style="padding-right: 40px">
12:         <table border="1">
13:             <tr>
14:                 <c:forEach items="${cpu}" var="c">
15:                     <td>Name</td>
16:                     <td>${c.name}</td>
17:                 </c:forEach>


Stacktrace:
    org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:574)
    org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:461)
    org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:396)
    org.apache.jasper.servlet.JspServlet.service(JspServlet.java:340)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    org.springframework.web.servlet.view.InternalResourceView.renderMergedOutputModel(InternalResourceView.java:168)
    org.springframework.web.servlet.view.AbstractView.render(AbstractView.java:303)
    org.springframework.web.servlet.DispatcherServlet.render(DispatcherServlet.java:1243)
    org.springframework.web.servlet.DispatcherServlet.processDispatchResult(DispatcherServlet.java:1027)
    org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:971)
    org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:893)
    org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:968)
    org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:870)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:648)
    org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:844)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    org.apache.catalina.filters.SetCharacterEncodingFilter.doFilter(SetCharacterEncodingFilter.java:108)
root cause

javax.servlet.ServletException: javax.servlet.jsp.JspTagException: Don't know how to iterate over supplied "items" in &lt;forEach&gt;
    org.apache.jasper.runtime.PageContextImpl.doHandlePageException(PageContextImpl.java:909)
    org.apache.jasper.runtime.PageContextImpl.handlePageException(PageContextImpl.java:838)
    org.apache.jsp.WEB_002dINF.views.cart_jsp._jspService(cart_jsp.java:156)
    org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
    org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:438)
    org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:396)
    org.apache.jasper.servlet.JspServlet.service(JspServlet.java:340)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    org.springframework.web.servlet.view.InternalResourceView.renderMergedOutputModel(InternalResourceView.java:168)
    org.springframework.web.servlet.view.AbstractView.render(AbstractView.java:303)
    org.springframework.web.servlet.DispatcherServlet.render(DispatcherServlet.java:1243)
    org.springframework.web.servlet.DispatcherServlet.processDispatchResult(DispatcherServlet.java:1027)
    org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:971)
    org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:893)
    org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:968)
    org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:870)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:648)
    org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:844)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    org.apache.catalina.filters.SetCharacterEncodingFilter.doFilter(SetCharacterEncodingFilter.java:108)
root cause

javax.servlet.jsp.JspTagException: Don't know how to iterate over supplied "items" in &lt;forEach&gt;
    org.apache.taglibs.standard.tag.common.core.ForEachSupport.toForEachIterator(ForEachSupport.java:274)
    org.apache.taglibs.standard.tag.common.core.ForEachSupport.supportedTypeForEachIterator(ForEachSupport.java:238)
    org.apache.taglibs.standard.tag.common.core.ForEachSupport.prepare(ForEachSupport.java:155)
    javax.servlet.jsp.jstl.core.LoopTagSupport.doStartTag(LoopTagSupport.java:256)
    org.apache.jsp.WEB_002dINF.views.cart_jsp._jspx_meth_c_005fforEach_005f0(cart_jsp.java:178)
    org.apache.jsp.WEB_002dINF.views.cart_jsp._jspService(cart_jsp.java:138)
    org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
    org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:438)
    org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:396)
    org.apache.jasper.servlet.JspServlet.service(JspServlet.java:340)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    org.springframework.web.servlet.view.InternalResourceView.renderMergedOutputModel(InternalResourceView.java:168)
    org.springframework.web.servlet.view.AbstractView.render(AbstractView.java:303)
    org.springframework.web.servlet.DispatcherServlet.render(DispatcherServlet.java:1243)
    org.springframework.web.servlet.DispatcherServlet.processDispatchResult(DispatcherServlet.java:1027)
    org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:971)
    org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:893)
    org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:968)
    org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:870)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:648)
    org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:844)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    org.apache.catalina.filters.SetCharacterEncodingFilter.doFilter(SetCharacterEncodingFilter.java:108)

cart.jsp

<body>
    <div style="padding-right: 40px">
        <table border="1">
            <tr>
                <c:forEach items="${cpu}" var="c">
                    <td>Name</td>
                    <td>${c.name}</td>
                </c:forEach>



    </div>

控制器 @Controller

public class CartController {

    @RequestMapping(value = "/cart", method = RequestMethod.POST)
    public String someAction(@ModelAttribute("cpu") Cpu cpu, Model model) {
        model.addAttribute("cpu", cpu);
        return "cart";
    }
}

CPU

@SuppressWarnings("serial")
public class Cpu implements Serializable {

    public static final String SESSION_PROPERTY = "cpu";

    private int id;

    private String name;

    private String socket;

    private int price;

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

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

    public String getSocket() {
        return socket;
    }

    public void setSocket(String socket) {
        this.socket = socket;
    }

    public int getPrice() {
        return price;
    }

    public void setPrice(int price) {
        this.price = price;
    }

}

Answer 1

您尝试使用<c:forEach>在自定义Cpu类型的单个实例上进行迭代，而迭代的明显要求是......拥有可以使用的对象集合迭代。这就是JSTL规范所说的：

  

<c:forEach>支持大量集合类型，包括java.util.Collection的所有实现（包括List，LinkedList，ArrayList，Vector，Stack，Set）和java.util.Map（包括HashMap，Hashtable，Properties，Provider，Attributes）。

     

（...）

     

java.util.Iterator和java.util.Enumeration的实现是   也支持（...）。

应该更改控制器以创建List<Cpu>，稍后将通过model属性将其传递给JSP页面。在在线商店中实施购物车的常用习惯是使用HttpSession来累积所有用户的商品。稍后，您可以在CartController中访问此共享会话对象，并检索用户放在那里的所有项目。