使用 Jackson 将 Json 解析为 POJO

Question

我有以下json

{
    "root": {
        "status": "UP",
        "connection1": {
            "status": "UP"
        },
        "connection2": {
            "status": "UP"
        }
    }
}

我还有以下 POJO classes 我想将 JSON 转换成

@JsonIgnoreProperties(ignoreUnknown = true)
public class POJO {

    @JsonProperty("root")
    @JsonDeserialize(using = RootDeserializer.class)
    private Root root;

    //getters + setters
}

public class Root {

    private boolean isAlive;
    private List<Connection> connections;

    public Root(boolean isAlive, List<Connection> connections) {
        this.isAlive = isAlive;
        this.connections = connections;
    }

    //getters + setters
}

@JsonIgnoreProperties(ignoreUnknown = true)
public class Connection {

    private String status;

    //getters + setters
}

最后我有了这个反序列化器来将 json 转换为 Root 实例

public class RootDeserializer extends JsonDeserializer<Root> {

    private static final String CONNECTION_PREFIX = "connection";
    private static final String UP_STATUS = "UP";

    private ObjectMapper objectMapper = new ObjectMapper();

    @Override
    public Root deserialize(JsonParser parser, DeserializationContext context) throws IOException {
        Map<String, Map<String, Object>> rootJsonMap = parser.readValueAs(Map.class);

        boolean isAlive = StringUtils.equals(UP_STATUS, String.valueOf(rootJsonMap.get("status")));
        List<Connection> connections = rootJsonMap.entrySet()
                .stream()
                .filter(entry -> StringUtils.startsWithIgnoreCase(entry.getKey(), CONNECTION_PREFIX))
                .map(this::mapToConnection)
                .collect(Collectors.toList());

        return new Root(isAlive, connections);
    }

    private PosServerConnection mapToConnection(Map.Entry<String, Map<String, Object>> entry) {
        Map<String, Object> connectionJsonMap = entry.getValue();
        return objectMapper.convertValue(connectionJsonMap, Connection.class);
    }
}

这样我就可以将我所有的连接分组到根 class 中的一个列表中。我的问题是还有其他方法可以做到这一点吗？？

我想在没有这么大的反序列化器的情况下只使用我的 Pojo 上的 Jackson 注释来做到这一点 classes

Answer 1

您可以简单地通过使用 @JsonAnySetter 注释为 List<Connection> 自定义 Setter 来实现这一点，如下所示。您也可以参考 Jackson Annotation Examples 来了解它是如何工作的。

POJO

public class Pojo {
    private Root root;

    //general getters, setters and toString
}

public class Root {
    private String status;
    private List<Connection> connections = new ArrayList<>();

    public List<Connection> getConnections() {
        return connections;
    }

    @JsonAnySetter
    public void setConnections(String name, Connection connection) {
        connection.setName(name);
        this.connections.add(connection);
    }

    //other getters, setters and toString
}

public class Connection {
    private String name;
    private String status;

    //general getters, setters and toString
}

然后你可以将给定的 JSON 字符串序列化为 Pojo 用普通的方式 Jackson:

代码段

ObjectMapper mapper = new ObjectMapper();
Pojo pojo = mapper.readValue(jsonStr, Pojo.class);
System.out.println(pojo.getRoot().getConnections().toString());

控制台输出

[Connection [name=connection1, status=UP], Connection [name=connection2, status=UP]]

使用 Jackson 将 Json 解析为 POJO

Parse Json into POJO using Jackson

java

json

jackson

objectmapper