引起:java.lang.NoClassDefFoundError:com/fasterxml/jackson/databind/JsonMappingException $ Reference

Question

我是Java的新手.我正在尝试显示JSON数据,因为我决定去杰克逊图书馆.但是我得到了错误.

我在用

jackson-annotations-2.3.0.jar
jackson-core-2.4.2.jar
jackson-databind-2.4.2.jar

这是我的对象,在这里我有一个依赖"tnStudentLocLog"

public class Student implements java.io.Serializable, WorkItem {

    private int studentId;
    private Date date;
    private Date startTime;
    private Date endtime;
    private int room;
    private Set tnStudentLocLog;

    public Student() {
    }

    public Student(int studentId,Date date, int room, Date startTime, Date endtime) {
        this.studentId = studentId;
        this.date = date;
        this.room = room;
        this.startTime = startTime;
        this.endtime = endtime;
    }
}

UserController类:

 @Controller
@RequestMapping(value="/students")
public class StudentController {


    private static Logger logger = Logger.getLogger( StudentController.class);


    private StudentManagerDelegate studentDelegate;  


    public StudentController() throws Exception
    {
        studentDelegate= new StudentManagerDelegate(ServiceType.LOCAL);
    }
    /********* GET ALL STUDENTS  ************/
    @RequestMapping(method=RequestMethod.GET)
    @ResponseStatus(HttpStatus.OK)
    public @ResponseBody SuccessResponse<List<Student>> getAllStudents() throws Exception {
        Map<String,List<Student>> studentsMap = new HashMap<String,List<Student>>();
        SuccessResponse<List<Student>> resp = new SuccessResponse<List<Student>>();
        resp.list = studentDelegate.load();
        return resp;
    }

在这里,我得到了正确的结果.但是,"studentId":2正在循环自己,如下所示

     {"max":"30","list":[{"studentId":2,"date":1339327730000,"startTime":1339327806000,"endtime":1339329470000,"room":0,"tnStudentLocLog":
[{"id":"studentId":2,"inTime":1339327872000},"sequenceId":2,"outTime":1339327967000,"Student":{"studentId":2,"date":1339327730000,"startTime":1339327806000,"endtime":1339329470000,"tnStudentLocLog":[{"id":{"studentId":2,"room":10,"inTime":1339327872000},"sequenceId":2,"outTime":1339327967000,"Student":{"studentId":2,"date":1339327730000,"startTime":1339327806000,"endtime":1339329470000,"tnStudentLocLog":[{"id":.......

但是,在我输入"/ students/4"时的URL中.它显示正确.我不知道究竟发生了什么.我看到很多帖子,他们正在改变杰克逊核心的版本,注释.但是,这不符合我的情况.

在此先感谢您的帮助.

Answer 1

欢迎来到java。使用 Java 时需要学习的第一件事就是如何设置和使用 CLASSPATH。“Class Not Found”错误意味着您的一个或多个 jar 文件不在类路径中。Java 不会隐式地在任何地方（甚至不是类所在的子目录）查找 .jar 文件。你必须告诉它去哪里寻找。如何设置 CLASSPATH？这取决于您的平台（Windows、Linux、IIS、Apache、Tomcat、Bluejay、Eclipse 等...）学好，您将避免许多头痛。