Java 没有从字符串值（'；'；）反序列化的字符串参数构造函数/工厂方法

使用

com.fasterxml.jackson.databind

包中的

ObjectMapper

类时，我遇到了一个json解析问题，我得到的错误是：

com.fasterxml.jackson.databind.JsonMappingException: Can not construct instance of com.graybar.utilities.ups.beans.Address: no String-argument constructor/factory method to deserialize from String value ('')

出现此问题的web应用程序是一个使用AngularJS前端的Spring MVC应用程序，但我可以用一个更小的全java程序来复制此问题。这是我的豆子：

shipping.java

@JsonIgnoreProperties(ignoreUnknown = true)
public class Shipment {
    @JsonProperty("Activity")
    private ArrayList<Activity> activity;
    public ArrayList<Activity> getActivity() {
        return activity;
    }
    public void setActivity(ArrayList<Activity> activity) {
        this.activity = activity;
    }
}

Address.java

@JsonIgnoreProperties(ignoreUnknown = true)
public class Address {
    @JsonProperty("City")
    private String city;
    @JsonProperty("StateProvinceCode")
    private String stateProvinceCode;
    @JsonProperty("CountryCode")
    private String countryCode;
    public String getCity() {
        return city;
    }
    public void setCity(String city) {
        this.city = city;
    }
    public String getCountryCode() {
        return countryCode;
    }
    public void setCountryCode(String countryCode) {
        this.countryCode = countryCode;
    }
    public String getStateProvinceCode() {
        return stateProvinceCode;
    }
    public void setStateProvinceCode(String stateProvinceCode) {
        this.stateProvinceCode = stateProvinceCode;
    }
}

下面是我可以正确映射json的代码：

public static void main(String[] args) {
    String jsonMessage = "" +
        "{" + 
        "   \"Activity\": [{ " +
        "       \"ActivityLocation\": { " +
        "           \"Address\": { " +
        "               \"City\": \"Hana\", " +
        "               \"StateProvinceCode\": \"Hi\", " +
        "               \"CountryCode\": \"US\" " +
        "           } " +
        "       } " +
        "   }, " +
        "   { " +
        "       \"ActivityLocation\": { " +
        "           \"Address\": { " +
        "               \"City\": \"Honolulu\", " +
        "               \"StateProvinceCode\": \"Hi\", " +
        "               \"CountryCode\": \"US\" " +
        "           } " +
        "       } " +
        "   }] " +
    "} ";

    try {
        ObjectMapper mapper = new ObjectMapper();
        mapper.enable(DeserializationFeature.ACCEPT_SINGLE_VALUE_AS_ARRAY);

        Shipment shipment = mapper.readValue(jsonMessage, Shipment.class);
        System.out.println("shipment.toString = " + shipment.toString());
    } catch (Exception e) {
        e.printStackTrace();
    }
}

在调整

jsonMessage

var中的数据时，我遇到了上面提到的错误：

    "{" + 
    "   \"Activity\": [{ " +
    "       \"ActivityLocation\": { " +
    "           \"Address\": { " +
    "               \"City\": \"Hana\", " +
    "               \"StateProvinceCode\": \"Hi\", " +
    "               \"CountryCode\": \"US\" " +
    "           } " +
    "       } " +
    "   }, " +
    "   { " +
    "       \"ActivityLocation\": { " +
    "           \"Address\": \"\" " +
    "           } " +
    "       } " +
    "   }] " +
    "} ";

因此，从以下位置更改json时会出现问题：

{
    "ActivityLocation": { 
        "Address": {
            "City": "Honolulu", 
            "StateProvinceCode": "Hi", 
            "CountryCode": "US"
        }
    }
}]

为此：

{
"ActivityLocation": {
     "Address": ""
    }
}

我得到的只是一个空字符串，而不是为我的

地址
bean发送值。不幸的是，我从第三方接收数据，无法控制我接收的数据

是否需要添加注释才能处理此问题？
尝试设置映射器.configure（反序列化配置.Feature.ACCEPT_EMPTY_STRING_AS_NULL_OBJECT，true）

或

取决于你的杰克逊版本

mapper.enable(DeserializationFeature.ACCEPT_EMPTY_STRING_AS_NULL_OBJECT);

我的代码和上面的答案一样好用。
原因是来自jackson的json与从controller发送的json不同

String test1= mapper.writeValueAsString(result1);

json类似（通常可以反序列化）：

但是json从另一个服务发送，如下所示：

{"code":200,"message":"查询桌面列表成功","data":[{"nics":"","status":"","metadata":"","desktopOperatorType":"","marker":"","user_name":"csrgzbsjy","user_group":"ADMINISTRATORS","user_email":"","product_id":"","image_id":"","computer_name":"B-jiegou-all-15","desktop_id":"6360ee29-eb82-416b-aab8-18ded887e8ff","created":"2018-11-12T07:45:15.000Z","ip_address":"192.168.2.215","security_groups":"","root_volume":"","data_volumes":"","availability_zone":"","ou_name":"","login_status":"","desktop_ip":"","ad_id":""},{"nics":"","status":"","metadata":"","desktopOperatorType":"","marker":"","user_name":"glory_2147","user_group":"ADMINISTRATORS","user_email":"","product_id":"","image_id":"","computer_name":"H-pkpm-all-357","desktop_id":"709164e4-d3e6-495d-9c1e-a7b82e30bc83","created":"2018-11-09T09:54:09.000Z","ip_address":"192.168.2.235","security_groups":"","root_volume":"","data_volumes":"","availability_zone":"","ou_name":"","login_status":"","desktop_ip":"","ad_id":""}]}

您可以在不启动的情况下处理参数时注意到差异。
小心点，我不小心打电话的时候有这个

mapper.convertValue(...)

而不是

mapper.readValue(...)

所以，请确保调用正确的方法，因为参数相同，IDE可以找到很多东西
此异常表示您正在尝试从字符串“\”\”反序列化对象“地址”，而不是像“{…}”这样的对象描述。反序列化程序找不到带字符串参数的地址构造函数。您必须将“”替换为{}以避免此错误。
我找到了另一种处理此错误的方法。（变量与原问题一致）

使用下面的代码片段，这对我很有用

ObjectMapper objectMapper = new ObjectMapper();
String jsonString = "{\"symbol\":\"ABCD\}";
objectMapper.configure(DeserializationFeature.ACCEPT_EMPTY_STRING_AS_NULL_OBJECT, true);
Trade trade = objectMapper.readValue(jsonString, new TypeReference<Symbol>() {});

如果我正在解析的json没有任何空值或空值，那么引发此异常的原因是什么？我只是想更好地理解所有内容。@Kervvv如果输入没有任何空字符串，则不会引发此异常。您的回答补充了什么，而我的答案不是1.5年前的？@AbhijitSarkar什么？问题是错误“没有要反序列化的字符串参数构造函数/工厂方法…”。SO不仅要回答具体问题，还要回答整个问题。我在输入稍有不同的情况下遇到了这个问题，但我正经历着调试这个问题的相同过程。我已经发布了我的答案，因为它可能有助于调试这个特定的问题，但稍微改变了环境。第二点是，人们会用这种输入搜索问题，这可能会帮助他们。输入是相同的，情况是不同的，有相同的例外。这个答案对我很有帮助。我也有同样的例外。这个答案解决了我的问题。这是其中一个问题。。。这个答案在过去的一周里帮了我两次忙。（我真惭愧）这就是这次例外的确切原因！读了这篇评论后，我马上找出了错误！！泰！这是正确的答案！！
{"code":200,"message":"查询桌面列表成功","data":[{"nics":"","status":"","metadata":"","desktopOperatorType":"","marker":"","user_name":"csrgzbsjy","user_group":"ADMINISTRATORS","user_email":"","product_id":"","image_id":"","computer_name":"B-jiegou-all-15","desktop_id":"6360ee29-eb82-416b-aab8-18ded887e8ff","created":"2018-11-12T07:45:15.000Z","ip_address":"192.168.2.215","security_groups":"","root_volume":"","data_volumes":"","availability_zone":"","ou_name":"","login_status":"","desktop_ip":"","ad_id":""},{"nics":"","status":"","metadata":"","desktopOperatorType":"","marker":"","user_name":"glory_2147","user_group":"ADMINISTRATORS","user_email":"","product_id":"","image_id":"","computer_name":"H-pkpm-all-357","desktop_id":"709164e4-d3e6-495d-9c1e-a7b82e30bc83","created":"2018-11-09T09:54:09.000Z","ip_address":"192.168.2.235","security_groups":"","root_volume":"","data_volumes":"","availability_zone":"","ou_name":"","login_status":"","desktop_ip":"","ad_id":""}]}

mapper.convertValue(...)

mapper.readValue(...)

   JsonNode parsedNodes = mapper.readValue(jsonMessage , JsonNode.class);
        Response response = xmlMapper.enable(ACCEPT_EMPTY_STRING_AS_NULL_OBJECT,ACCEPT_SINGLE_VALUE_AS_ARRAY )
                .disable(FAIL_ON_UNKNOWN_PROPERTIES, FAIL_ON_IGNORED_PROPERTIES)
                .convertValue(parsedNodes, Response.class);

ObjectMapper objectMapper = new ObjectMapper();
String jsonString = "{\"symbol\":\"ABCD\}";
objectMapper.configure(DeserializationFeature.ACCEPT_EMPTY_STRING_AS_NULL_OBJECT, true);
Trade trade = objectMapper.readValue(jsonString, new TypeReference<Symbol>() {});

@JsonIgnoreProperties    public class Symbol {
    @JsonProperty("symbol")
    private String symbol;
}