我正在尝试序列化一个"持有者"类,该类中有一个值,其类型派生自泛型。 即"类HasValue"内部有一个"私有A值"。
此外,我还有接口"Inf"和一个实现该接口的具体类"InfCls"。界面标有@JsonTypeInfo,并被告知创建一个"@class"字段。
如果持有者类没有@JsonTypeInfo,一切正常。但是当我补充说它坏了。
注意:虽然在这种情况下我不需要@JsonTypeInfo(因为持有者始终是一个具体的类),但在需要时会出现同样的问题,所以我选择这个作为更简单的例子。
以下为:
import static org.junit.Assert.assertEquals;
import java.util.Objects;
import org.junit.Test;
import com.fasterxml.jackson.annotation.JsonAutoDetect;
import com.fasterxml.jackson.annotation.JsonCreator;
import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.annotation.JsonTypeInfo;
import com.fasterxml.jackson.annotation.JsonTypeInfo.As;
import com.fasterxml.jackson.databind.JavaType;
import com.fasterxml.jackson.databind.ObjectMapper;
public class SerializationIssues {
// No @JsonTypeInfo on HasValue
@Test
public void json_HasValue_Inf_javaType() throws Exception {
HasValue<Inf> object = new HasValue<>(new InfCls(1));
ObjectMapper objectMapper = new ObjectMapper();
JavaType javaType = objectMapper.getDeserializationConfig().getTypeFactory().constructParametricType(HasValue.class, Inf.class);
String serialized = objectMapper.writerFor(javaType).writeValueAsString(object);
HasValue<?> deserialized = objectMapper.readValue(serialized, javaType);
assertEquals(object, deserialized);
}
// @JsonTypeInfo on HasValueId
@Test
public void json_HasValueId_Inf_javaType() throws Exception {
HasValueId<Inf> object = new HasValueId<>(new InfCls(1));
ObjectMapper objectMapper = new ObjectMapper();
JavaType javaType = objectMapper.getDeserializationConfig().getTypeFactory().constructParametricType(HasValueId.class, Inf.class);
String serialized = objectMapper.writerFor(javaType).writeValueAsString(object);
HasValueId<?> deserialized = objectMapper.readValue(serialized, javaType);
assertEquals(object, deserialized);
}
// ===== An interface and impl to test @JsonTypeInfo =====
@JsonTypeInfo(use = JsonTypeInfo.Id.MINIMAL_CLASS, include = As.PROPERTY, property = "@class")
public static interface Inf {
}
@JsonAutoDetect(fieldVisibility = JsonAutoDetect.Visibility.ANY, isGetterVisibility = JsonAutoDetect.Visibility.NONE, getterVisibility = JsonAutoDetect.Visibility.NONE, setterVisibility = JsonAutoDetect.Visibility.NONE)
public static class InfCls implements Inf {
private int val;
@JsonCreator
public InfCls(@JsonProperty("val") int val) {
this.val = val;
}
@Override
public String toString() {
return "InfCls [val=" + val + "]";
}
@Override
public int hashCode() {
return 31 * 1 + val;
}
@Override
public boolean equals(Object obj) {
if (this == obj)
return true;
if (obj == null)
return false;
if (getClass() != obj.getClass())
return false;
InfCls other = (InfCls) obj;
if (val != other.val)
return false;
return true;
}
}
// ===== A class that has a value =====
@JsonAutoDetect(fieldVisibility = JsonAutoDetect.Visibility.ANY, isGetterVisibility = JsonAutoDetect.Visibility.NONE, getterVisibility = JsonAutoDetect.Visibility.NONE, setterVisibility = JsonAutoDetect.Visibility.NONE)
public static class HasValue<A> {
private final A val;
@JsonCreator
public HasValue(@JsonProperty("val") A val) {
this.val = Objects.requireNonNull(val);
}
public A get() {
return val;
}
@Override
public String toString() {
return "HasValue [val=" + val + "]";
}
@Override
public int hashCode() {
return 31 * 1 + ((val == null) ? 0 : val.hashCode());
}
@Override
public boolean equals(Object obj) {
if (this == obj)
return true;
if (obj == null)
return false;
if (getClass() != obj.getClass())
return false;
HasValue<?> other = (HasValue<?>) obj;
if (val == null) {
if (other.val != null)
return false;
} else if (!val.equals(other.val))
return false;
return true;
}
}
@JsonTypeInfo(use = JsonTypeInfo.Id.MINIMAL_CLASS, include = JsonTypeInfo.As.PROPERTY, property = "@class")
@JsonAutoDetect(fieldVisibility = JsonAutoDetect.Visibility.ANY, isGetterVisibility = JsonAutoDetect.Visibility.NONE, getterVisibility = JsonAutoDetect.Visibility.NONE, setterVisibility = JsonAutoDetect.Visibility.NONE)
public static class HasValueId<A> {
private final A val;
@JsonCreator
public HasValueId(@JsonProperty("val") A val) {
this.val = Objects.requireNonNull(val);
}
public A get() {
return val;
}
@Override
public String toString() {
return "HasValue [val=" + val + "]";
}
@Override
public int hashCode() {
return 31 * 1 + ((val == null) ? 0 : val.hashCode());
}
@Override
public boolean equals(Object obj) {
if (this == obj)
return true;
if (obj == null)
return false;
if (getClass() != obj.getClass())
return false;
HasValueId<?> other = (HasValueId<?>) obj;
if (val == null) {
if (other.val != null)
return false;
} else if (!val.equals(other.val))
return false;
return true;
}
}
}
一旦遇到@JsonTypeInfo
注释,您引导时使用的序列化程序就会被推开,并且您提供的类型信息正在丢失。
有几种方法可以解决此问题。您可以在类中提供显式类型信息:
public static class HasValueId<A extends Inf> {
private final A val;
这将允许杰克逊通过内省确定字段类型并找到您的第二个注释。
或者您可以使用 @JsonTypeInfo
注释通用字段:
public static class HasValueId<A> {
@JsonTypeInfo(use = JsonTypeInfo.Id.MINIMAL_CLASS, include = As.PROPERTY, property = "@class")
private final A val;
。这将避免在界面上进行注释的需要。
完成此操作后,您将不再需要键入您的编写器; 普通的旧objectMapper.writeValueAsString(object);
将起作用。