如何用杰克逊反序列化枚举?

Question

用户 POST{"lang": ["en_US", "en_UK"]}到 REST API。我想填充一个具有此属性的对象List<EnmLanguage> lang;.除了 JSON 数组之外，其他所有事情都有效。

我的语言.java是：

@JsonSerialize(
using = BaseEnumSerializer.class
)
@JsonDeserialize(
using = BaseEnumDeserializer.class
)
public enum EnmLanguage implements BaseEnum, Serializable {
en_US {
public String getCode() {
return "en_US";
}
public String getText(EnmLanguage s) {
return s == EnmLanguage.en_US ? "English" : "İngilizce";
}
},

我的基本.java是：

public interface BaseEnum {
Object getCode();
String getText(EnmLanguage lang);
default String getText() {
return this.getText(EnmLanguage.tr_TR);
}
default Map<String, Object> getMap(EnmLanguage lang) {
return new HashMap<String, Object>() {
{
this.put("name", BaseEnum.this.getText(lang));
this.put("id", BaseEnum.this.getCode());
}
};
}
default Map<String, Object> getMap() {
return this.getMap(EnmLanguage.tr_TR);
}
static <T extends Enum<T> & BaseEnum> T fromCode(Class<T> parent, Object code) {
Map<Object, T> lookup = new HashMap();
Enum[] var3 = (Enum[])parent.getEnumConstants();
int var4 = var3.length;
for(int var5 = 0; var5 < var4; ++var5) {
T d = var3[var5];
lookup.put(((BaseEnum)d).getCode().toString(), d);
}
return (Enum)lookup.get(code.toString());
}
}

My BaseEnumDeserialiazer 是：

public class BaseEnumDeserializer<T extends Enum<T> & BaseEnum> extends StdDeserializer<T> {
public BaseEnumDeserializer() {
this((Class)null);
}
public BaseEnumDeserializer(Class<T> vc) {
super(vc);
}
public T deserialize(JsonParser jsonparser, DeserializationContext context) throws IOException {
Field field = this.findField(jsonparser.getCurrentName(), jsonparser.getCurrentValue().getClass());
Class<T> javaType = field.getType();
return BaseEnum.fromCode(javaType, jsonparser.getText());
}
public Field findField(String name, Class<?> c) {
while(c != null) {
Field[] var3 = c.getDeclaredFields();
int var4 = var3.length;
for(int var5 = 0; var5 < var4; ++var5) {
Field field = var3[var5];
if (!Modifier.isStatic(field.getModifiers()) && field.getName().equals(name)) {
return field;
}
}
c = c.getSuperclass();
}
return null;
}
}

但最终它并没有将"lang": ["en_US", "en_UK"]转换为EnmLanguage的List。我认为它不知道该转换为哪个BaseEnum。我应该如何让它知道它应该将其转换为List<EnmLanguage>？

Answer 1

对于您的具体情况，在基类型中添加静态@JsonCreator方法可能就足够了。

interface Lang {
@JsonCreator
static Lang valueOf(String value) {
return Languages.valueOf(value);
}
}
@JsonFormat(shape = JsonFormat.Shape.STRING)
enum Languages implements Lang {
en_US,
en_GB
}

然后你可以像任何其他类一样解析它

class LangTest {
private final ObjectMapper mapper = new ObjectMapper()
.setAnnotationIntrospector(new JacksonAnnotationIntrospector());
@Test
void readsJson() throws IOException {
final Lang[] tree = this.mapper
.readerFor(Lang[].class)
.readValue("["en_US", "en_GB"]");
Assertions.assertArrayEquals(
tree,
new Lang[]{
Languages.en_US,
Languages.en_GB
}
);
}
}

Answer 2

这是一个简单的BaseEnum界面，

public interface BaseEnum {
Object getCode();
String getText();
}

下面是实现BaseEnum接口EnmLanguage，

public enum EnmLanguage implements BaseEnum {
en_US("en_US", "English"),
en_UK("en_UK", "English"),
tr_TR("tr_TR", "Turkish");
private String code;
private String text;
EnmLanguage(String code, String text) {
this.code = code;
this.text = text;
}
@Override
public String getCode() {
return code;
}
@Override
public String getText() {
return text;
}
}

这是实现BaseEnum接口的另一个EnmElement，

public enum EnmElement implements BaseEnum {
H("H", "Hydrogen"),
He("He", "Helium"),
Li("Li", "Lithium");
private String code;
private String text;
EnmElement(String code, String text) {
this.code = code;
this.text = text;
}
@Override
public String getCode() {
return code;
}
@Override
public String getText() {
return text;
}
}

这是一个简单的单元测试，

import com.fasterxml.jackson.databind.ObjectMapper;
import org.junit.Test;
import java.io.IOException;
import static org.junit.Assert.assertArrayEquals;
import static org.junit.Assert.assertEquals;
import static org.junit.Assert.assertNotNull;
public class EnumTest {
@Test
public void testDeserializeLanguage() throws IOException {
ObjectMapper mapper = new ObjectMapper();
EnmLanguage[] expected = {EnmLanguage.en_US, EnmLanguage.tr_TR};
EnmLanguage[] actual = mapper
.readerFor(EnmLanguage[].class)
.readValue(mapper.writeValueAsString(expected));
assertNotNull(actual);
assertArrayEquals(expected, actual);
}
@Test
public void testDeserializeElement() throws IOException {
ObjectMapper mapper = new ObjectMapper();
EnmElement[] expected = {EnmElement.H, EnmElement.He, EnmElement.Li};
EnmElement[] actual = mapper
.readerFor(EnmElement[].class)
.readValue(mapper.writeValueAsString(expected));
assertNotNull(actual);
assertArrayEquals(expected, actual);
}
}

使用枚举的一个稍微复杂的例子，

import lombok.Data;
@Data
public class CompositeExample {
private String name;
private EnmLanguage[] lands;
private EnmElement[] elements;
}

一个示例单元测试片段，

@Test
public void testDeserialize() throws IOException {
CompositeExample expected = new CompositeExample();
String name = "Hello";
expected.setName(name);
EnmLanguage[] langs = {EnmLanguage.en_US, EnmLanguage.tr_TR};
expected.setLangs(langs);
EnmElement[] elements = {EnmElement.H, EnmElement.He,  EnmElement.Li};
expected.setElements(elements);
ObjectMapper mapper = new ObjectMapper();
String json = mapper.writeValueAsString(expected);
//{"name":"Hello","langs":["en_US","tr_TR"],"elements":["H","He","Li"]}
CompositeExample actual = mapper
.readerFor(CompositeExample.class)
.readValue(json);
assertNotNull(actual);
assertEquals(expected, actual);
}

Answer 3

尝试使用toString()启用读取和写入枚举：

objectMapper.configure(SerializationFeature.WRITE_ENUMS_USING_TO_STRING, true);
objectMapper.configure(DeserializationFeature.READ_ENUMS_USING_TO_STRING, true);