Jackson 无法使用 ObjectMapper 映射类

Question

我正在尝试使用 Jackson 序列化一个包含两个字符串和字符串到字符串的映射的类。这是我要序列化的json。我想知道是否有问题，因为我正在尝试序列化空数组。

{
    "filters": {
        "test": [
            "hi"
        ],
        "groups": [],
        "groupsOT": [],
        "chains": [],
        "chainsOT": [],
        "locations": [],
        "locationsOT": [],
        "reports": [],
        "reportsOT": []
    },
    "fromDate": "09.03.2015",
    "toDate": "16.03.2015"
}

这是用于尝试序列化的类。

public class FilterRequest{
    public String getToDate() {
        return toDate;
    }

    public void setToDate(String toDate) {
        this.toDate = toDate;
    }

    public String getFromDate() {
        return fromDate;
    }

    public void setFromDate(String fromDate) {
        this.fromDate = fromDate;
    }

    public Map<String, String[]> getFilters() {
        return filters;
    }

    public void setFilters(Map<String, String[]> filters) {
        this.filters = filters;
    }

    private String toDate;
    private String fromDate;
    private Map<String,String[]> filters;

    public FilterRequest(){
        filters = new HashMap<String,String[]>();
    }


}

失败的代码很简单

    ObjectMapper mapper = new ObjectMapper();
    FilterRequest requestParams = mapper.readValue(requestBody, FilterRequest.class);

我得到的错误是

No suitable constructor found for type [simple type, class com.aramburu.overall.web.controller.FilterController$FilterRequest]: can not instantiate from JSON object (need to add/enable type information?)
at [Source: {"filters":{"test":["hi"],"groups":[],"groupsOT":[],"chains":[],"chainsOT":[],"locations":[],"locationsOT":[],"reports":[],"reportsOT":[]},"fromDate":"09.03.2015","toDate":"16.03.2015"}; line: 1, column: 2]

Answer 1

输出： No suitable constructor found for type [simple type, class com.aramburu.overall.web.controller.FilterController$FilterRequest 暗示 FilterRequest 是一个内部类。

将 FilterRequest 类设为静态（或者 - 更好的是 - 将其移出 FilterController）。

否则 Jackson 无法实例化它（它需要父类的外部实例才能构造内部实例）。

Answer 2

如果您的类被声明为内部类，则需要将其设为静态。例如：

public class Application {

    private static final String requestBody = "{\"filters\": {\"test\": [\"hi\"],\"groups\": [],\"groupsOT\": [],\"chains\": [],\"chainsOT\": [],\"locations\": [],\"locationsOT\": [],\"reports\": [],\"reportsOT\": []},\"fromDate\": \"09.03.2015\",\"toDate\": \"16.03.2015\"}";


    public static void main(String[] args) throws IOException {
        ObjectMapper mapper = new ObjectMapper();
        FilterRequest requestParams = mapper.readValue(requestBody, FilterRequest.class);

        System.out.println(requestParams);
    }

    public static class FilterRequest{
        public String getToDate() {
            return toDate;
        }

        public void setToDate(String toDate) {
            this.toDate = toDate;
        }

        public String getFromDate() {
            return fromDate;
        }

        public void setFromDate(String fromDate) {
            this.fromDate = fromDate;
        }

        public Map<String, String[]> getFilters() {
            return filters;
        }

        public void setFilters(Map<String, String[]> filters) {
            this.filters = filters;
        }

        private String toDate;
        private String fromDate;
        private Map<String,String[]> filters;

        public FilterRequest(){
            filters = new HashMap<String,String[]>();
        }

        @Override
        public String toString() {
            return ToStringBuilder.reflectionToString(this, ToStringStyle.DEFAULT_STYLE);
        }
    }
}

问候，