java - 使用 Jackson 将对象转换为 JSON 时的无限递归

Question

我有一个类，用于存储工具的首选项。此类使用 toString() 将自身转换为 JSON。当我将对象转换为 JSON 时，出现无限递归错误，但我不明白为什么。我没有任何循环引用，所以这让我有点困惑。任何帮助将不胜感激。

这是我的类结构:

public class ToolPrefs
{
   private boolean isFloating;
   private ToolPalettePlacement placement; //this is an enum
   private boolean isSelected;
   private int dockLocation;
   private Point dialogLocation;
   private Dimension dialogSize;

   public ToolPrefs(){}

   public boolean isFloating(){return isFloating; }

   public void setFloating(boolean floating){ isFloating = floating; }

   public ToolPalettePlacement getPlacement(){ return placement; }

   public void setPlacement(ToolPalettePlacement placement){ this.placement = placement;}

   public boolean isSelected(){ return isSelected;}

   public void setSelected(boolean selected){isSelected = selected;}

   public int getDockLocation(){return dockLocation;}

   public void setDockLocation(int dockLocation){this.dockLocation = dockLocation; }

   public Point getDialogLocation(){return dialogLocation;}

   public void setDialogLocation(Point dialogLocation){ this.dialogLocation = dialogLocation;}

   public Dimension getDialogSize(){ return dialogSize; }

   public void setDialogSize(Dimension dialogSize){this.dialogSize = dialogSize;}


   @JsonIgnore @Override
   public String toString()
   {
      String json;
      ObjectWriter ow = new ObjectMapper().writer().withDefaultPrettyPrinter();
      try
      {
         json = ow.writeValueAsString(this);
      }
      catch (IOException e)
      {
         e.printStackTrace();
         json = "";
      }
      return json;
   }
}

这是我收到的异常片段:

com.fasterxml.jackson.databind.JsonMappingException: Infinite recursion (StackOverflowError) (through reference chain: java.awt.Point["location"]->java.awt.Point["location"]->java.awt.Point["location"]->java.awt.Point["location"]...) at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:518) at com.fasterxml.jackson.databind.ser.BeanSerializer.serialize(BeanSerializer.java:117) at com.fasterxml.jackson.databind.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:464) at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:504) at com.fasterxml.jackson.databind.ser.BeanSerializer.serialize(BeanSerializer.java:117) at com.fasterxml.jackson.databind.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:464) at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:504) at com.fasterxml.jackson.databind.ser.BeanSerializer.serialize(BeanSerializer.java:117) at com.fasterxml.jackson.databind.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:464) at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:504) at com.fasterxml.jackson.databind.ser.BeanSerializer.serialize(BeanSerializer.java:117)

Answer 1

您面临的问题是由于您的对象嵌入的 Point 类造成的。

要解决此问题，您可以指示 Jackson 在第一层深度停止，要实现此解决方案，您可以按照以下步骤操作:

1)首先，您必须运行 2.x 版本的 Jackson，我已经用以下方法测试了解决方案:

<dependencies>
    <dependency>
        <groupId>com.fasterxml.jackson.core</groupId>
        <artifactId>jackson-databind</artifactId>
        <version>2.8.3</version>
    </dependency>
</dependencies>

2) 当您初始化 ObjectMapper 的新实例时，请执行以下操作:

ObjectWriter ow = new ObjectMapper().configure(DEFAULT_VIEW_INCLUSION, true).writer().withDefaultPrettyPrinter();

3) 如果您有 Point 类型，请使用注释:

@JsonView(Point.class) Point dialogLocation;

jackson 将停在第一层，结果将是:

{
  "dialogLocation" : {
    "x" : 2.0,
    "y" : 3.0
  }
}

有关更多文档，您可以查看以下内容:

Limit Jackson output to only one level

Enable default view inclusion on Jackson 2.x ObjectMapper

我已经测试了该解决方案，只要您使用 Jackson 的 2.x 版本，它就可以工作。对于 1.x，我还无法让它运行。