toString() function for JPA one-to-many relations raises StackOverflowError

Question

I have two JPA Entity classes, Task and TaskList. There's a one-to-many relationship between TaskList and Task (obviously) with the tasklist_id foreign key in the task table.

The Task class is this:

@Entity(name = "task")
public class Task implements Serializable {    

    // Id and 3 fields

    @ManyToOne
    @JoinColumn(name="tasklist_id")
    private TaskList parentList;

    // 3 more fields

    // Constructor
    public Task() {}

    //Getters and Setters
}

and the TaskList class is this:

@Entity(name = "task_list")
public class TaskList implements Serializable {

    // Id and two fields

    @OneToMany(mappedBy="parentList")
    private List<Task> tasks;

    // Constructor
    public TaskList() {}
}

When I try to add an automatic getter and setter to these two classes and a toString() function, I get a StackOverflowError.

How do I go about writing getters and setters for the two fields so that I get a proper object with toString()?

Pretty like it is not a JPA/Hibernate. Read this [question](http://stackoverflow.com/questions/3593893/why-im-getting-stackoverflowerror), maybe it can be relevant to you. — Bonifacio, Feb 05 '16 at 13:11

cst1992 · Accepted Answer · 2016-02-08T14:21:11.547

4

To future readers, the solution is to use back references:

Task class:

@Entity(name = "task")
public class Task implements Serializable {    

    // Id and 3 fields

    @JsonBackReference("task_list-task")
    @ManyToOne
    @JoinColumn(name="tasklist_id")
    private TaskList parentList;

    // 3 more fields

    // Constructor
    public Task() {}

    //Getters and Setters
}

TaskList class

@Entity(name = "task_list")
public class TaskList implements Serializable {

    // Id and two fields

    @JsonManagedReference("task_list-task")
    @OneToMany(mappedBy="parentList")
    private List<Task> tasks;

    // Constructor
    public TaskList() {}
}

Add the proper annotations. Add ManagedReference to @OneToMany(parent) and BackReference to @ManyToOne(child). Write table names in the brackets as indicated, separated by a hyphen.

This takes care of the infinite recursion automatically, solving the StackOverflowError problem.

Some links:

http://keenformatics.blogspot.in/2013/08/how-to-solve-json-infinite-recursion.html
http://vard-lokkur.blogspot.in/2010/10/json-jackson-to-rescue.html

edited Feb 08 '16 at 14:21

answered Feb 08 '16 at 13:05

cst1992

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Your answer isn't corresponding your question. Your question was about `toString()` implementation, not about conversion objects net to JSON. :) – v.ladynev Feb 08 '16 at 14:18
This solution solves the fundamental problem - infinite recursion - that results from using toString() directly. Jackson is used there, as shown in the error log, so these annotations are relevant. Also, I've tested this in my own code personally. :) – cst1992 Feb 08 '16 at 14:20
There are not an error log, jackson or json tags in your question. :) – v.ladynev Feb 08 '16 at 14:22
@v.ladynev Also, I have tried other ways, and none worked the way this did. Not to mention they were making writing some of other functions extremely difficult. – cst1992 Feb 08 '16 at 14:23

score 1 · Answer 2 · answered Feb 05 '16 at 13:16

When you do tasks.toString() the default implementation of toString() in the AbstractCollection call toString() for the every element in the list (for every Task). So you should not to use a default implementation and get information from the tasks in a loop and don't call toString() for every Task of course. You can get from the Task and add to a result string task's id or name.

toString() function for JPA one-to-many relations raises StackOverflowError

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