問題描述

我在嘗試獲取 JSON 請求并對其進行處理時收到以下錯誤:

I am getting the following error when trying to get a JSON request and process it:

org.codehaus.jackson.map.JsonMappingException:沒有找到適合類型 [simple type, class com.myweb.ApplesDO] 的構造函數(shù):無法從 JSON 對象實例化(需要添加/啟用類型信息?)

org.codehaus.jackson.map.JsonMappingException: No suitable constructor found for type [simple type, class com.myweb.ApplesDO]: can not instantiate from JSON object (need to add/enable type information?)

這是我要發(fā)送的 JSON:

Here is the JSON I am trying to send:

{
  "applesDO" : [
    {
      "apple" : "Green Apple"
    },
    {
      "apple" : "Red Apple"
    }
  ]
}

在Controller中，我有以下方法簽名:

In Controller, I have the following method signature:

@RequestMapping("showApples.do")
public String getApples(@RequestBody final AllApplesDO applesRequest){
    // Method Code
}

AllApplesDO 是 ApplesDO 的包裝器:

AllApplesDO is a wrapper of ApplesDO :

public class AllApplesDO {

    private List<ApplesDO> applesDO;

    public List<ApplesDO> getApplesDO() {
        return applesDO;
    }

    public void setApplesDO(List<ApplesDO> applesDO) {
        this.applesDO = applesDO;
    }
}

ApplesDO:

public class ApplesDO {

    private String apple;

    public String getApple() {
        return apple;
    }

    public void setApple(String appl) {
        this.apple = apple;
    }

    public ApplesDO(CustomType custom){
        //constructor Code
    }
}

我認為 Jackson 無法將 JSON 轉換為子類的 Java 對象.請幫助杰克遜將 JSON 轉換為 Java 對象的配置參數(shù).我正在使用 Spring 框架.

I think that Jackson is unable to convert JSON into Java objects for subclasses. Please help with the configuration parameters for Jackson to convert JSON into Java Objects. I am using Spring Framework.

在上述示例類中包含導致此問題的主要錯誤 - 請查看已接受的解決方案答案.

Included the major bug that is causing this problem in the above sample class - Please look accepted answer for solution.

推薦答案

所以，我終于意識到問題所在了.這不是我懷疑的杰克遜配置問題.

So, finally I realized what the problem is. It is not a Jackson configuration issue as I doubted.

其實問題出在ApplesDO類:

public class ApplesDO {

    private String apple;

    public String getApple() {
        return apple;
    }

    public void setApple(String apple) {
        this.apple = apple;
    }

    public ApplesDO(CustomType custom) {
        //constructor Code
    }
}

為該類定義了一個自定義構造函數(shù)，使其成為默認構造函數(shù).引入虛擬構造函數(shù)使錯誤消失:

There was a custom constructor defined for the class making it the default constructor. Introducing a dummy constructor has made the error to go away:

public class ApplesDO {

    private String apple;

    public String getApple() {
        return apple;
    }

    public void setApple(String apple) {
        this.apple = apple;
    }

    public ApplesDO(CustomType custom) {
        //constructor Code
    }

    //Introducing the dummy constructor
    public ApplesDO() {
    }

}

這篇關于JsonMappingException:沒有為類型 [簡單類型，類] 找到合適的構造函數(shù):無法從 JSON 對象實例化的文章就介紹到這了，希望我們推薦的答案對大家有所幫助，也希望大家多多支持html5模板網(wǎng)！