Solution to Infinite Recursion Problem of Interrelated Entities in Java

Directory Java Infinite Recursion of Interrelated Entities Before Jackson 2.0, the solution is to have a good understanding of the idea of recursion in Java, the conditional elements of recursion, the algorithm structure of recursion, and the actual combat example of recursion. Summary 1

Java Infinite Recursion of Interrelated Entities

Today, an bug appeared during the test, and an error was reported in the process of serializing the associated entity and returning it, prompting

Caused by: java.lang.StackOverflowError: null

This is a stack overflow error. Looking up the error thread, we finally find that Column and Table entities are related to each other, that is,

There are Table attribute in Column entity and Column attribute in Table entity, which leads to infinite loop, infinite recursion and stack overflow error in the serialization process.

The solution prior to Jackson 2.0 was

Add on the associated property

@JsonBackReference

Or

@JsonIgnore

One of the annotations will do. However, starting with Jackson 2.0 and later, the @ JsonIdentityInfo annotation is provided to solve this problem, with annotations before entity classes

@JsonIdentityInfo(generator=ObjectIdGenerators.IntSequenceGenerator.class, property="@id")

A good understanding of recursion in Java

The idea of recursion

Transform large-scale problems into small-scale similar sub-problems to solve them. When the function is implemented, because the method to solve the big problem and the method to solve the small problem are often the same method, the function calls itself. In addition, this problem solving function must have obvious ending conditions, so that there will be no infinite recursion.

1 sentence summary: Recursion is to call yourself.

Conditional elements of recursion

1. There are two important conditions for recursion

You can reduce the size of the problem by recursive calls, and the new problem has the same form as the original problem. (Self-invocation) There is a simple situation, which can make recursion exit in a simple situation. (Recursive exit)

2. 3 Elements of Recursion

Try to simplify a problem to a smaller scale Parent problem and child problem cannot overlap 1 There must be 1 situation in which you can exit the program

Recursive algorithm structure

The common algorithm pseudo-code of recursion is as follows:

func( mode){
    if(endCondition){      // Recursive exit 
          end;
    }else{
         func(mode_small)  // Call itself, recursively 
    }
}

Examples of recursive actual combat

Recursion is still a little abstract. Let's look at the code directly

1. The recursive realization of Fibonacci number

The recurrence formula of Fibonacci sequence is Fib (n) = Fib (n-1) + Fib (n-2), and the sequence (1, 1, 2, 3, 5, 8...) is generated.

public static int fib(int n) throws Exception {
    if (n < 0){
        throw new Exception(" Please enter the correct parameters ");
   } else if (n == 0 || n == 1){
        return n;
   } else {
        return fib(n - 1) + fib(n - 2); //  Call yourself 
   }
}

Recursive Implementation of 2, 99 Multiplication Table

public static void mul(int n){
        if(n==1){
            System.out.println("1*1=1");
        }else {
            mul(n -1);
            for(int i=1;i<=n;i++){
                System.out.println(i + "*" + n + "=" + i*n + " ");
            }
        }
    }

Summary 1, please

Recursive algorithm is an algorithm that calls itself directly or indirectly. If a problem can be solved, it can be decomposed into the solutions of several sub-problems; This problem is different from the sub-problem after decomposition, except for the different data scale, and the solution idea is completely the same; And there are obvious recursive termination conditions. Then recursion will be a good choice.