Jackson bug（或功能！？）在使用java.util.Set时 - mySet.size（）始终为1 [英] Jackson bug (or feature!?) when using java.util.Set - mySet.size() is always 1

问题描述

我正在使用Jackson 2.2.0和Spring 3.2.0与Hibernate 4.2.2。

I am using Jackson 2.2.0 and Spring 3.2.0 with Hibernate 4.2.2.

我最近不得不通过POST将一组对象发送到服务器：

I recently had to send an array of objects via POST to the server:

{"cancelationDate":"2013-06-05",
 "positions":[
   {"price":"EUR 12.00",
    "count":1},
   {"price":"EUR 99.00",
    "count":1}
 ]
}

我的课程如下：

public class Bill extends {
  LocalDate cancelationDate;

  Set<Position> positions;

  ...
}

和：

public class Position { 
  Integer count;

  BigMoney price;

  @JsonIgnore
  Bill bill;

  ...
}

当我打电话给 bill.getPositions（）。size（）它告诉我 1 。

When I call bill.getPositions().size() it tells me 1.

如果我使用列表< Position> 而不是设置< Position> 它很好用。那么设置的问题是什么？

If I use List<Position> instead of Set<Position> it works nice. So what's the problem with Set?

谢谢：）

public int hashCode() {
    final int prime = 31;
    int result = 1;
    result = (int) (prime * result + ((id == null) ? 0 : id.hashCode()));
    return result;
}

public boolean equals(Object obj) {
    if (obj == this)
        return true;
    if (!(obj instanceof Position))
        return false;
    Position equalCheck = (Position) obj;
    if ((id == null && equalCheck.id != null) || (id != null && equalCheck.id == null))
        return false;
    if (id != null && !id.equals(equalCheck.id))
        return false;
    return true;
}   

推荐答案

由于id为null Jackson反序列化了Positions，hashCode为不同的对象返回相同的值，equals返回true。 Set不能包含相同的元素。修复你的equals / hashcode实现，一切都会正常工作。

Since id is null for the Jackson deserialized Positions, hashCode returns the same value for the different objects, and equals returns true. A Set cannot contain to elements which are equal. Fix your equals/hashcode implentation and everything will work as it should.

建议的新hashCode /等于：

Suggested new hashCode/equals:

public int hashCode() {
    final int prime = 31;
    int result = 1;
    result = (int) (prime * result + ((id == null) ? 0 : id.hashCode()));
    result = (int) (prime * result + ((price== null) ? 0 : price.hashCode()));
    return result;
}

public boolean equals(Object obj) {
    if (obj == this)
        return true;
    if (!(obj instanceof Position))
        return false;
    Position equalCheck = (Position) obj;
    if ((id == null && equalCheck.id != null) || (id != null && equalCheck.id == null))
        return false;
    if (id != null && !id.equals(equalCheck.id))
        return false;
    if ((price== null && equalCheck.price != null) || (price != null && equalCheck.price == null))
        return false;
    if (price!= null && !price.equals(equalCheck.idprice)
        return false;

    return true;
}   

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