我使用JAVA 1.6和Jackson 1.9.9，我有一个enum
public enum Event {
FORGOT_PASSWORD("forgot password");
private final String value;
private Event(final String description) {
this.value = description;
}
@JsonValue
final String value() {
return this.value;
}
}
我已经添加了一个@JsonValue，这似乎做的工作，它序列化对象:
{"event":"forgot password"}
但当我尝试反序列化时，我得到
Caused by: org.codehaus.jackson.map.JsonMappingException: Can not construct instance of com.globalrelay.gas.appsjson.authportal.Event from String value 'forgot password': value not one of declared Enum instance names
我错过了什么?
可以采用多种方法将JSON对象反序列化为枚举。我最喜欢的风格是创建一个内部类:
import com.fasterxml.jackson.annotation.JsonCreator;
import com.fasterxml.jackson.annotation.JsonFormat;
import com.fasterxml.jackson.annotation.JsonProperty;
import org.hibernate.validator.constraints.NotEmpty;
import java.util.Arrays;
import java.util.Map;
import java.util.function.Function;
import java.util.stream.Collectors;
import static com.fasterxml.jackson.annotation.JsonFormat.Shape.OBJECT;
@JsonFormat(shape = OBJECT)
public enum FinancialAccountSubAccountType {
MAIN("Main"),
MAIN_DISCOUNT("Main Discount");
private final static Map<String, FinancialAccountSubAccountType> ENUM_NAME_MAP;
static {
ENUM_NAME_MAP = Arrays.stream(FinancialAccountSubAccountType.values())
.collect(Collectors.toMap(
Enum::name,
Function.identity()));
}
private final String displayName;
FinancialAccountSubAccountType(String displayName) {
this.displayName = displayName;
}
@JsonCreator
public static FinancialAccountSubAccountType fromJson(Request request) {
return ENUM_NAME_MAP.get(request.getCode());
}
@JsonProperty("name")
public String getDisplayName() {
return displayName;
}
private static class Request {
@NotEmpty(message = "Financial account sub-account type code is required")
private final String code;
private final String displayName;
@JsonCreator
private Request(@JsonProperty("code") String code,
@JsonProperty("name") String displayName) {
this.code = code;
this.displayName = displayName;
}
public String getCode() {
return code;
}
@JsonProperty("name")
public String getDisplayName() {
return displayName;
}
}
}
我发现了一个非常好的和简洁的解决方案，特别是当您不能修改枚举类时，就像在我的例子中一样。然后，您应该提供一个启用了特定特性的自定义ObjectMapper。这些特性从Jackson 1.6开始就可以使用了。所以你只需要在你的enum中写入toString()方法。
public class CustomObjectMapper extends ObjectMapper {
@PostConstruct
public void customConfiguration() {
// Uses Enum.toString() for serialization of an Enum
this.enable(WRITE_ENUMS_USING_TO_STRING);
// Uses Enum.toString() for deserialization of an Enum
this.enable(READ_ENUMS_USING_TO_STRING);
}
}
还有更多与枚举相关的特性可用，请参见这里:
https://github.com/FasterXML/jackson-databind/wiki/Serialization-Features
https://github.com/FasterXML/jackson-databind/wiki/Deserialization-Features
如果您希望将枚举类与其JSON表示完全解耦，@xbakesx指出的序列化器/反序列化器解决方案是一个很好的解决方案。
或者，如果您更喜欢自包含的解决方案，那么基于@JsonCreator和@JsonValue注释的实现将更方便。
因此，利用@Stanley的例子，下面是一个完整的自包含解决方案(Java 6, Jackson 1.9):
public enum DeviceScheduleFormat {
Weekday,
EvenOdd,
Interval;
private static Map<String, DeviceScheduleFormat> namesMap = new HashMap<String, DeviceScheduleFormat>(3);
static {
namesMap.put("weekday", Weekday);
namesMap.put("even-odd", EvenOdd);
namesMap.put("interval", Interval);
}
@JsonCreator
public static DeviceScheduleFormat forValue(String value) {
return namesMap.get(StringUtils.lowerCase(value));
}
@JsonValue
public String toValue() {
for (Entry<String, DeviceScheduleFormat> entry : namesMap.entrySet()) {
if (entry.getValue() == this)
return entry.getKey();
}
return null; // or fail
}
}
可以采用多种方法将JSON对象反序列化为枚举。我最喜欢的风格是创建一个内部类:
import com.fasterxml.jackson.annotation.JsonCreator;
import com.fasterxml.jackson.annotation.JsonFormat;
import com.fasterxml.jackson.annotation.JsonProperty;
import org.hibernate.validator.constraints.NotEmpty;
import java.util.Arrays;
import java.util.Map;
import java.util.function.Function;
import java.util.stream.Collectors;
import static com.fasterxml.jackson.annotation.JsonFormat.Shape.OBJECT;
@JsonFormat(shape = OBJECT)
public enum FinancialAccountSubAccountType {
MAIN("Main"),
MAIN_DISCOUNT("Main Discount");
private final static Map<String, FinancialAccountSubAccountType> ENUM_NAME_MAP;
static {
ENUM_NAME_MAP = Arrays.stream(FinancialAccountSubAccountType.values())
.collect(Collectors.toMap(
Enum::name,
Function.identity()));
}
private final String displayName;
FinancialAccountSubAccountType(String displayName) {
this.displayName = displayName;
}
@JsonCreator
public static FinancialAccountSubAccountType fromJson(Request request) {
return ENUM_NAME_MAP.get(request.getCode());
}
@JsonProperty("name")
public String getDisplayName() {
return displayName;
}
private static class Request {
@NotEmpty(message = "Financial account sub-account type code is required")
private final String code;
private final String displayName;
@JsonCreator
private Request(@JsonProperty("code") String code,
@JsonProperty("name") String displayName) {
this.code = code;
this.displayName = displayName;
}
public String getCode() {
return code;
}
@JsonProperty("name")
public String getDisplayName() {
return displayName;
}
}
}
