Spring MVC，捕获对象列表，如@ModelAttribute

Question

我有 Test 类，并且我有 jsp 页面，其中包含绑定到测试对象列表的输入。我想用编辑过的信息从我的 jsp 中取回我的测试列表。 我的测试班是：

@Entity
@Table(name = "[NewMVC].[dbo].[Tests]")
public class Test {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id")
    private int id; 

    @Column(name = "testQuestion")
    private String testQuestion;

    @Column(name = "optionOne")
    private String optionOne;

    @Column(name = "optionTwo")
    private String optionTwo;

    @Column(name = "optionThree")
    private String optionThree;

    @Column(name = "subjectType")
    private int subjectType;

    @Column(name = "correctOptionNumber")
    private int correctOptionNumber; 
        //gets, sets...

我有一个 jsp，我可以在其中编辑带有测试的列表：

   <form:form action="saveTestsEdits" method="POST" modelAttribute = "testWrapper">

    <c:forEach items="${testWrapper.testList}" var="test" varStatus="i">
    <h2> Test number ${i.index+1} </h2>
    <form:hidden value="${test.id}" path = "testList[${i.index}].id" />
    <table>
        <tr><td>Test Question:</td> <td><form:input path = "testList[${i.index}].testQuestion" value = "${test.testQuestion}"/> </td></tr>
        <tr><td>Option one: </td> <td><form:input path = "testList[${i.index}].optionOne" value= "${test.optionOne}"/> </td>
        <td>        
        <c:choose>
        <c:when test="${test.correctOptionNumber == 1}"> <form:radiobutton path = "testList[${i.index}].correctOptionNumber" value = "1" checked = "checked"/> </c:when>
        <c:otherwise><form:radiobutton path = "testList[${i.index}].correctOptionNumber" value = "1"/> </c:otherwise> 
        </c:choose> 
        </td>
        </tr>

        <tr><td>Option two: </td> <td><form:input path = "testList[${i.index}].optionTwo" value= "${test.optionTwo}"/> </td>
        <td>        
        <c:choose>
        <c:when test="${test.correctOptionNumber == 2}"> <form:radiobutton path = "testList[${i.index}].correctOptionNumber" value = "2" checked = "checked"/> </c:when>
        <c:otherwise><form:radiobutton path = "testList[${i.index}].correctOptionNumber" value = "2"/> </c:otherwise> 
        </c:choose> 
        </td>
        </tr>


        <tr><td>Option three: </td> <td><form:input path = "testList[${i.index}].optionThree" value= "${test.optionThree}"/> </td>
        <td>        
        <c:choose>
        <c:when test="${test.correctOptionNumber == 3}"> <form:radiobutton path = "testList[${i.index}].correctOptionNumber" value = "3" checked = "checked"/> </c:when>
        <c:otherwise><form:radiobutton path = "testList[${i.index}].correctOptionNumber" value = "3"/> </c:otherwise> 
        </c:choose> 
        </td>

        </tr>
        <tr><th>Subject type:</th></tr>
        <tr><td>Georaphy: </td> 
        <td>        
        <c:choose>
        <c:when test="${test.subjectType == 3}"> <form:radiobutton path = "testList[${i.index}].subjectType" value = "3" checked = "checked"/> </c:when>
        <c:otherwise><form:radiobutton path = "testList[${i.index}].subjectType" value = "3"/></c:otherwise> 
        </c:choose> 
        </td>
        </tr>

        <tr><td>Mathematics: </td> 
        <td>        
        <c:choose>
        <c:when test="${test.subjectType == 4}"><form:radiobutton path = "testList[${i.index}].subjectType" value = "4" checked = "checked"/> </c:when>
        <c:otherwise><form:radiobutton path = "testList[${i.index}].subjectType" value = "4"/></c:otherwise> 
        </c:choose> 
        </td>
        </tr>

        <tr><td>History: </td> 
        <td>        
        <c:choose>
        <c:when test="${test.subjectType == 5}"><form:radiobutton path = "testList[${i.index}].subjectType" value = "5" checked = "checked"/> </c:when>
        <c:otherwise><form:radiobutton path = "testList[${i.index}].subjectType" value = "5"/></c:otherwise> 
        </c:choose> 
        </td>
        </tr>

    </table>
    <br>        
    </c:forEach>
    <input type="submit" value="Submit" />
</form:form>
</body>
</html>

实际上我并没有清楚地发送到页面列表，但我有一个名为 TestWrapper 的特殊类，它看起来像：

public class TestWrapper {

    private List<Test> testList = null;

    public TestWrapper(List<Test> testList) {

        this.testList = testList;
    }

    public void setTestList(List<Test> testList) {

        this.testList = testList;
    }

    public List<Test> getTestList() {

        return testList;
    }

}

我尝试使用：

@RequestMapping(value="/saveTestsEdits", method = RequestMethod.POST)
     public String register(@ModelAttribute("testWrapper")TestWrapper testWrapper , HttpServletRequest request)

但它给了我一个例外：

SEVERE: Servlet.service() for servlet [appServlet] in context with path [/mvc] threw exception [Request processing failed; nested exception is org.springframework.beans.BeanInstantiationException: Could not instantiate bean class [com.andrew.models.TestWrapper]: No default constructor found; nested exception is java.lang.NoSuchMethodException: com.andrew.models.TestWrapper.<init>()] with root cause
java.lang.NoSuchMethodException: com.andrew.models.TestWrapper.<init>()

非常感谢！

Answer 1

当JVM无法实例化xxx类的对象时，抛出异常java.lang.NoSuchMethodException: xxx.<init>()。在这种情况下，Spring 不能实例化 TestWrapper 类。

您有一个列表参数构造函数，但不是默认的。添加如下：

public class TestWrapper {

    public TestWrapper() {
    }
}