杰克逊无法实例化 ArrayList

Question

我想发送以下 POST 请求：

POST: /api/test
{
   "words": ["running", "testing", "and"]
}

我的控制器如下所示：

@RequestMapping(value={"/api/test"}, method=RequestMethod.POST)
@ResponseBody
public ResponseEntity<Text> getWords(@RequestBody Words words) {
    // Do something with words...
    return new ResponseEntity<Text>(new Text("test"), HttpStatus.OK);
}

单词类：

public class Words {

    private List<String> words;

    public Words(List<String> words) {
        this.words = words;
    }

    public List<String> getWords() {
        return words;
    }
}

发送字符串而不是列表时，它可以正常工作，但是使用列表时出现以下错误：

Could not read document:
No suitable constructor found for type [simple type, class api.models.tokenizer.Words]: can not instantiate from JSON object (need to add/enable type information?)\n at [Source: java.io.PushbackInputStream@60f2a08; line: 2, column: 5]; nested exception is com.fasterxml.jackson.databind.JsonMappingException: No suitable constructor found for type [simple type, class api.models.tokenizer.Words]: can not instantiate from JSON object (need to add/enable type information?)\n at [Source: java.io.PushbackInputStream@60f2a08; line: 2, column: 5]

Answer 1

默认情况下，Jackson 使用默认构造函数创建类的实例。你没有。所以，要么添加构造函数

public Words() {}

或者使用注解@JsonCreator标记现有的构造函数：

@JsonCreator
public Words(@JsonProperty("words") List<String> words) {
    this.words = words;
}