我有一个学生班，与学科班级有一对多关联：
public class Student implements Serializable{
/**
*
*/
private static final long serialVersionUID = -779930820340758193L;
private int studentId;
private String studentName;
private List<Subject> subjectList;
public Student(int studentId, String studentName, List<Subject> subjectList) {
super();
this.studentId = studentId;
this.studentName = studentName;
this.subjectList = subjectList;
}
public Student() {
}
public int getStudentId() {
return studentId;
}
public void setStudentId(int studentId) {
this.studentId = studentId;
}
public String getStudentName() {
return studentName;
}
public void setStudentName(String studentName) {
this.studentName = studentName;
}
public List<Subject> getSubjectList() {
return subjectList;
}
public void setSubjectList(List<Subject> subjectList) {
this.subjectList = subjectList;
}
@Override
public String toString() {
return "Student [studentId=" + studentId + ", studentName="
+ studentName + ", subjectList=" + subjectList + "]";
}
}
主题：
public class Subject implements Serializable{
/**
*
*/
private static final long serialVersionUID = 7135393884889475409L;
private int subjectId;
private String subjectName;
public Subject(int subjectId, String subjectName) {
super();
this.subjectId = subjectId;
this.subjectName = subjectName;
}
public int getSubjectId() {
return subjectId;
}
public void setSubjectId(int subjectId) {
this.subjectId = subjectId;
}
public String getSubjectName() {
return subjectName;
}
public void setSubjectName(String subjectName) {
this.subjectName = subjectName;
}
@Override
public int hashCode() {
final int prime = 31;
int result = 1;
result = prime * result + subjectId;
result = prime * result
+ ((subjectName == null) ? 0 : subjectName.hashCode());
return result;
}
@Override
public boolean equals(Object obj) {
if (this == obj)
return true;
if (obj == null)
return false;
if (getClass() != obj.getClass())
return false;
Subject other = (Subject) obj;
if (subjectId != other.subjectId)
return false;
if (subjectName == null) {
if (other.subjectName != null)
return false;
} else if (!subjectName.equals(other.subjectName))
return false;
return true;
}
@Override
public String toString() {
return "Subject [subjectId=" + subjectId + ", subjectName="
+ subjectName + "]";
}
}
我的控制器返回所有科目的列表以及学生注册的科目，以便在视图中默认选中它们。
控制器：
public class HelloController{
@RequestMapping(value = "", method = RequestMethod.GET)
public String printHello(ModelMap model) {
model.addAttribute("message", "Hello Spring MVC Framework!");
List<Subject> allList = new ArrayList<Subject>();
allList.add(new Subject(1,"English"));
allList.add(new Subject(2,"Maths"));
allList.add(new Subject(3,"Science"));
allList.add(new Subject(4,"Social"));
allList.add(new Subject(5,"Tamil"));
List<Subject> enrolledList = new ArrayList<Subject>();
enrolledList.add(new Subject(1,"English"));
enrolledList.add(new Subject(3,"Science"));
Student student = new Student(1,"SRI",enrolledList);
model.addAttribute("student", student);
model.addAttribute("availableList", allList);
return "home";
}
@RequestMapping(value = "save" , method = RequestMethod.POST)
public String saveStudent(@ModelAttribute Student student , ModelMap model){
System.out.println(">>>>>>>>>>>>"+student);
model.addAttribute("finalStudent", student);
return "success";
}
针对home.jsp
<%@ taglib uri="http://www.springframework.org/tags/form" prefix="form"%>
<html>
<head>
<title>Hello World</title>
</head>
<body>
<h2>${student.studentName}</h2>
<form:form method="POST" action="save" modelAttribute="student">
<form:checkboxes title="Subjects taken" path="subjectList"
items="${availableList}" itemLabel="subjectName" element="div" />
<input type = "submit" value = "Save"/>
</form:form>
</body>
</html>
但是，在此表单的sumbit上，我收到以下错误：
org.springframework.web.util.NestedServletException: Request processing failed; nested exception is org.springframework.validation.BindException: org.springframework.validation.BeanPropertyBindingResult: 1 errors
Field error in object 'student' on field 'subjectList': rejected value [Subject [subjectId=1, subjectName=English],Subject [subjectId=3, subjectName=Science]]; codes [typeMismatch.student.subjectList,typeMismatch.subjectList,typeMismatch.java.util.List,typeMismatch]; arguments [org.springframework.context.support.DefaultMessageSourceResolvable: codes [student.subjectList,subjectList]; arguments []; default message [subjectList]]; default message [Failed to convert property value of type 'java.lang.String[]' to required type 'java.util.List' for property 'subjectList'; nested exception is java.lang.IllegalStateException: Cannot convert value of type [java.lang.String] to required type [com.sri.test.Subject] for property 'subjectList[0]': no matching editors or conversion strategy found]
org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:656)
org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:560)
javax.servlet.http.HttpServlet.service(HttpServlet.java:641)
javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
答案 0 :(得分：0)
您需要实现StringToSubjectConverter类将提交的字符串转换为Subject对象：
public class StringToSubjectConverter implements Converter<String, Subject> {
@Override
public Subject convert(String s) {
return ...; // your code to convert from `String` to `Subject`
}
}
使用Spring Conversion Service注册此转换器：
<mvc:annotation-driven conversion-service="conversionService" />
<bean id="conversionService" class="org.springframework.format.support.FormattingConversionServiceFactoryBean">
<property name="converters">
<set>
<bean class="package.StringToSubjectConverter" />
</set>
</property>
</bean>
答案 1 :(得分：0)
我已经解决了你的问题。在这里，您尝试将Subject对象的String数组绑定到Subject对象List，这是不可能将“String [] subject”转换为List，这里是使用checkboxe得到的值
"Subject [subjectId=1,subjectName=English]"
由于toString方法被覆盖，选择主题后会出现这种输出格式。
现在，Spring在内部尝试将此String或String [] {以及多项选择}转换为您的List。即使使用convert（）方法，也无法转换。
因此，您必须在save方法中创建逻辑，首先从String []中提取这些值，然后在从提取的值创建Subject后将其设置为Subject列表。
然后你需要将它设置为List方法的setter。
这是下面的代码，修改了两种方法
1）你的主题类的toString
@Override
public String toString() {
return "subjectId=" + subjectId + ",subjectName="+ subjectName;
}
2）HelloController的保存方法
@RequestMapping(value = "save.do", method = RequestMethod.POST)
public String saveStudent(@ModelAttribute Student student,
BindingResult result, HttpServletRequest request, ModelMap model) {
System.out.println(">>>>>>>>>>>>" + student);
int i = 0;
List<Subject> lSubjects=new ArrayList<Subject>();
String[] subjectsInString = request.getParameterValues("subjectList");
String[] eachSubject=null;
Subject subject=null;
int subjectId=0;
String subjectName=null;
if (result.hasErrors()) {
List<FieldError> fieldErrors = result.getFieldErrors();
while (i < fieldErrors.size()) {
System.out.println("Error: " + fieldErrors.get(i));
i++;
}
for (String subjectInString : subjectsInString) {
System.out.println(subjectInString);
eachSubject=subjectInString.split(",");
for(String value:eachSubject){
if(value.contains("subjectId"))
subjectId=Integer.parseInt(value.substring(value.lastIndexOf('=')+1,value.length()));
if(value.contains("subjectName"))
subjectName=value.substring(value.lastIndexOf('=')+1,value.length());
/**/
}
subject=new Subject(subjectId, subjectName);
lSubjects.add(subject);
//eachSubject
}
student.setSubjectList(lSubjects);
System.out.println("Subject List[ "+student.getSubjectList()+" ]");
} else {
model.addAttribute("finalStudent", student);
}
return "success";
}
我希望这会对你有帮助，如果你还面临问题，请告诉我。