如何在 JSP 中使用嵌套的 foreach 标签

Question

我使用 Struts2 框架和 JSP。我想在 JSP 中嵌套 foreach 标签，但我在内部 foreach 标签处遇到错误。

迭代嵌套对象时出现错误。

<c:forEach var="emp" items="${dept.emplyees}">

异常：

Caused by: javax.servlet.jsp.JspTagException: Don't know how to iterate over supplied "items" in &lt;forEach&gt;
    at org.apache.taglibs.standard.tag.common.core.ForEachSupport.toForEachIterator(ForEachSupport.java:274) ~[jstl-1.2.jar:1.2]
    at org.apache.taglibs.standard.tag.common.core.ForEachSupport.supportedTypeForEachIterator(ForEachSupport.java:238) ~[jstl-1.2.jar:1.2]
    at org.apache.taglibs.standard.tag.common.core.ForEachSupport.prepare(ForEachSupport.java:155) ~[jstl-1.2.jar:1.2]
    at javax.servlet.jsp.jstl.core.LoopTagSupport.doStartTag(LoopTagSupport.java:291) ~[javax.servlet.jsp.jstl-api-1.2.1.jar:1.2.1]
    at org.apache.jsp.views.Home.home_jsp._jspx_meth_c_005fforEach_005f1(home_jsp.java:364) ~[na:na]
    at org.apache.jsp.views.Home.home_jsp._jspService(home_jsp.java:159) ~[na:na]

下面是我使用 POJO 和 Struts Action 字段的示例代码。

JSP代码：

<c:forEach var="dept" items="${deptList}"> 
  <c:out value="${dept.deptname}"/> 
  <c:forEach var="emp" items="${dept.emplyees}"> 
    <c:out value="${emp.name}"/> 
  </c:forEach>
</c:forEach>

操作class：testAction：

class TestAction{
List<Department> deptList

public List<Department> getDeptList() {
        return deptList;
    }

    public void setDeptList(List<Department> deptList) {
        this.deptList = deptList;
    }
}

Deprtment POJO:

class Department{

private String deptname

List<Employee> emplyees;

    public List<Employee> getDeptList() {
        return emplyees;
    }

    public void setDeptList(List<Employee> emplyees) {
        this.emplyees = emplyees;
    }
}

Employee POJO:

class Employee{
    private String name;
}

Answer 1

要遍历对象的属性它不应该是 null 并且有一个 getter 方法。

private List<Employee> emplyees = new ArrayList<>();
public List<Employee> getEmplyees() { return emplyees; }

在页面上显示此属性之前，最好有一些值。您可以在操作中执行此操作，或者在 prepare() 中更好，让您的操作实现 Preparable interface.

Often the data used to populate a form control is dynamically generated, perhaps from a database. When the user submits the form, the Struts 2 validation interceptor attempts to validate the user's form input. If validation fails the Struts 2 framework returns the value "input" but the "input" action is not re-executed. Rather the view associated with the "input" result is rendered to the user. Usually this view is the page that displayed the original form.

This work-flow can cause a problem if one or more of the form fields or some other data displayed depends on a dynamic look-up that that is accomplished in the Action class's input method. Since the Action class's input method is not re-executed when validation fails, the view page may no longer have access to the correct information to create the form or other display information.

如何在 JSP 中使用嵌套的 foreach 标签

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jstl

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jsp-tags