错误：java.lang.NoSuchMethodException: java.lang.Long.<init>() in spring MVC

Error: java.lang.NoSuchMethodException: java.lang.Long.<init>() in spring MVC

提问by Khan

Getting this error while reading student object from database.

从数据库读取学生对象时出现此错误。

org.springframework.beans.BeanInstantiationException: Failed to instantiate [java.lang.Long]: No default constructor found; nested exception is java.lang.NoSuchMethodException: java.lang.Long.<init>()
org.springframework.beans.BeanUtils.instantiateClass(BeanUtils.java:107)

full stack trace:

完整的堆栈跟踪：

org.springframework.web.util.NestedServletException: Request processing failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [java.lang.Long]: No default constructor found; nested exception is java.lang.NoSuchMethodException: java.lang.Long.<init>()
    org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:978)
    org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:857)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:617)
    org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:842)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
root cause

org.springframework.beans.BeanInstantiationException: Failed to instantiate [java.lang.Long]: No default constructor found; nested exception is java.lang.NoSuchMethodException: java.lang.Long.<init>()
    org.springframework.beans.BeanUtils.instantiateClass(BeanUtils.java:107)
    org.springframework.web.bind.annotation.support.HandlerMethodInvoker.resolveModelAttribute(HandlerMethodInvoker.java:775)
    org.springframework.web.bind.annotation.support.HandlerMethodInvoker.resolveHandlerArguments(HandlerMethodInvoker.java:368)
    org.springframework.web.bind.annotation.support.HandlerMethodInvoker.invokeHandlerMethod(HandlerMethodInvoker.java:172)
    org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.invokeHandlerMethod(AnnotationMethodHandlerAdapter.java:446)
    org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.handle(AnnotationMethodHandlerAdapter.java:434)
    org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:943)
    org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:877)
    org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:966)
    org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:857)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:617)
    org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:842)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
root cause

java.lang.NoSuchMethodException: java.lang.Long.<init>()
    java.lang.Class.getConstructor0(Class.java:3082)
    java.lang.Class.getDeclaredConstructor(Class.java:2178)
    org.springframework.beans.BeanUtils.instantiateClass(BeanUtils.java:104)
    org.springframework.web.bind.annotation.support.HandlerMethodInvoker.resolveModelAttribute(HandlerMethodInvoker.java:775)
    org.springframework.web.bind.annotation.support.HandlerMethodInvoker.resolveHandlerArguments(HandlerMethodInvoker.java:368)
    org.springframework.web.bind.annotation.support.HandlerMethodInvoker.invokeHandlerMethod(HandlerMethodInvoker.java:172)
    org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.invokeHandlerMethod(AnnotationMethodHandlerAdapter.java:446)
    org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.handle(AnnotationMethodHandlerAdapter.java:434)
    org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:943)
    org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:877)
    org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:966)
    org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:857)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:617)
    org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:842)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:717)

Student.java

学生.java

@Entity
@Table(name="Student")
public class Student implements Serializable{
    private static final long serialVersionUID = 1L;

    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
    @Column(name="studentId")
    Long studentId;

    @Column(name="studentName")
    String studentName;

Controller.java

控制器.java

    @RequestMapping(value = "/read.html")
    public String readStudent(Model model, @ModelAttribute("studentId") Long studentId) {
        Student student = null;
        studentId = 2l;
        try{
            student = serviceFile.readStudent(studentId);
        }catch(Exception e){
            model.addAttribute("message", "Some thing went wrong !!!! Exception occoured");
            return "message";
        }   
        model.addAttribute("student", student);
        return "read";
    }

daoImpl.java

daoImpl.java

@Repository
@Transactional
public class DaoImplFile implements DaoFile {

    private EntityManager entityManager;

    public EntityManager getEntityManager() {
        return entityManager;
    }

    @PersistenceContext
    public void setEntityManager(EntityManager entityManager) {
        this.entityManager = entityManager;
    }

    @Override
    public Student read(Long studentId) throws NullPointerException {               
        Student student = entityManager.find(Student.class, studentId);
        if (student!=null) {
            return student;
        } else {
            return null;
        }
    }

采纳答案by achabahe

The @ModelAttribute("studentId") Long studentIdis the source of the problem, because spring doesn't find a method that can provide this Longobject, so it tries to instantiate one and pass it as a method argument. To solve this problemyou can either :

的@ModelAttribute("studentId") Long studentId是问题的根源，因为弹簧不会发现可以提供这样的一种方法Long的对象，所以它试图实例之一，并把它作为一个方法参数。要解决此问题，您可以：

• Delete @ModelAttribue from the method argument

  @RequestMapping(value = "/read.html")
  public String readStudent(Model model,Long studentId) {
      Student student = null;
      studentId = 2l;
      try {
          student = serviceFile.readStudent(studentId);
      } catch(Exception e){
          model.addAttribute("message", "Some thing went wrong !!!! Exception occured");
          return "message";
      }
      model.addAttribute("student", student);
      return "read";
  }
  

• Create a method that will provide that LongObjectin your controlle

  @ModelAttribute
  public void provideStudentId(Model model){
      model.addAttribute("studentId", new Long(1));
  }
  

• 从方法参数中删除@ModelAttribue

  @RequestMapping(value = "/read.html")
  public String readStudent(Model model,Long studentId) {
      Student student = null;
      studentId = 2l;
      try {
          student = serviceFile.readStudent(studentId);
      } catch(Exception e){
          model.addAttribute("message", "Some thing went wrong !!!! Exception occured");
          return "message";
      }
      model.addAttribute("student", student);
      return "read";
  }
  

• 创建一个将Long在您的控件中提供该对象的方法

  @ModelAttribute
  public void provideStudentId(Model model){
      model.addAttribute("studentId", new Long(1));
  }
  

---

---

Official Doc

官方文件

@RequestMapping(path = "/owners/{ownerId}/pets/{petId}/edit", method = RequestMethod.POST)
public String processSubmit(@ModelAttribute Pet pet) { }

Given the above example where can the Pet instance come from? There are several options:

1. It may already be in the model due to use of @SessionAttributes?—?see the section called “Using @SessionAttributes to store model attributes in the HTTP session between requests”.
2. It may already be in the model due to an @ModelAttribute method in the same controller?—?as explained in the previous section.
3. It may be retrieved based on a URI template variable and type converter (explained in more detail below).
4. It may be instantiated using its default constructor.

鉴于上面的例子，Pet 实例来自哪里？有几种选择：

1. 由于使用了@SessionAttributes，它可能已经在模型中？—？请参阅“使用@SessionAttributes 在请求之间的 HTTP 会话中存储模型属性”一节。
2. 由于同一控制器中的@ModelAttribute 方法，它可能已经在模型中？-？如上一节所述。
3. 可以基于 URI 模板变量和类型转换器（下面更详细地解释）来检索它。
4. 它可以使用其默认构造函数进行实例化。

EDIT
If the studentId was the parameter name sent from the UI you can use @RequestParamlike this

编辑
如果 studentId 是从 UI 发送的参数名称，您可以@RequestParam像这样使用

@RequestMapping(value = "/read.html")
public String readStudent(Model model, @RequestParam("studentId") Long studentId) {
    Student student = null;
    studentId = 2l;
    try {
        student = serviceFile.readStudent(studentId);
    } catch(Exception e) {
        model.addAttribute("message", "Some thing went wrong !!!! Exception occoured");
        return "message";
    }   
    model.addAttribute("student", student);
    return "read";
}

回答by Nir Levy

You should change your studentIdfield type from Longto long, it should fix it.

您应该将studentId字段类型从更改Long为long，它应该可以修复它。

And one more unrelated thing that just pops to my eyes, this:

还有一件不相关的事情突然出现在我的眼前，这个：

if (student!=null) {
  return student;
} else {
  return null;
}

Is exactly like saying this:

就像这样说：

return student;