我有我用它来查询一些数据的外部服务。该数据将在两种格式(第一个是这样的“传统”,但支持的需要)之一:
{
"foo": "John Smith"
}
要么
{
"foo": {
"name": "John Smith",
"bar": "baz"
}
}
这是我想要映射到以下POJO:
@Data
@AllArgsConstructor
@NoArgsConstructor
public class Outer {
private Foo foo;
@Data
@AllArgsConstructor
@NoArgsConstructor
public static class Foo {
String name;
String bar;
}
}
数据在第二格式(foo
是一个对象)应该被反序列化就像任何其他的POJO,但在第一格式给出的数据(foo
是字符串),把它变成一个实例Foo
,我想打电话new Foo(<foo>, null)
。要做到这一点,我创建了一个自定义解串器(@JsonComponent
意味着该解串器将一个有点-全球注册ObjectMapper
弹簧通过杰克逊Module
接口):
@JsonComponent
public class FooDeserializer extends JsonDeserializer<Outer.Foo> {
@Override
public Outer.Foo deserialize(JsonParser parser, DeserializationContext context)
throws IOException {
JsonNode node = parser.getCodec().readTree(parser);
if (node.isTextual()) {
return new Foo(node.asText(), null);
}
return <delegate to next applicable deserializer>;
}
}
我有麻烦搞清楚如何做到“授人以一个适用解串器”的一部分,因为每一个解决方案我已经尝试(例如parser.getCodec().treeToValue(node, Outer.Foo.class)
)再次使用相同的自定义解串器,引起无限递归结束。这甚至可能吗?
感谢schummar答案:我怎么叫从杰克逊定制的解串器的默认解串器。按照上面的答案,
1 @JsonComponent
注释应该从自定义序列中删除,因为我们需要建立基于默认的序列自定义序列化,这是不被支持@JsonComponent
。
2.注册一个SimpleModule
到ObjectMapper
一个BeanDeserializerModifier和修改串行的,我们与默认的序列构建自定义序列。
3.在serialize
自定义序列化的方法,处理的特殊情况,并委托系列化正常情况下,默认的序列。
下面的代码演示了如何实现上述各点。
大类
import java.io.IOException;
import com.fasterxml.jackson.core.JsonParseException;
import com.fasterxml.jackson.databind.BeanDescription;
import com.fasterxml.jackson.databind.DeserializationConfig;
import com.fasterxml.jackson.databind.JsonDeserializer;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.deser.BeanDeserializerModifier;
import com.fasterxml.jackson.databind.module.SimpleModule;
public class DelegateDeserializer {
public static void main(String[] args) throws JsonParseException, JsonMappingException, IOException {
ObjectMapper mapper = new ObjectMapper();
SimpleModule simpleModule = new SimpleModule();
simpleModule.setDeserializerModifier(new BeanDeserializerModifier() {
@Override
public JsonDeserializer<?> modifyDeserializer(DeserializationConfig config, BeanDescription beanDesc,
JsonDeserializer<?> deserializer) {
if (Outer.Foo.class.isAssignableFrom(beanDesc.getBeanClass())) {
return new FooDeserializer(deserializer, beanDesc.getBeanClass());
}
return deserializer;
}
});
mapper.registerModule(simpleModule);
Outer outer1 = mapper.readValue(getType1Json(), Outer.class);
Outer outer2 = mapper.readValue(getType2Json(), Outer.class);
System.out.println("deserialize json with object structure:");
System.out.println(outer1.getFoo().getName());
System.out.println(outer1.getFoo().getBar());
System.out.println("deserialize json with string field only:");
System.out.println(outer2.getFoo().getName());
System.out.println(outer2.getFoo().getBar());
}
private static String getType1Json() {
return " { "
+ " \"foo\": { "
+ " \"name\": \"John Smith\", "
+ " \"bar\": \"baz\" "
+ " } "
+ "} ";
}
private static String getType2Json() {
return " { "
+ " \"foo\": \"John Smith\" "
+ "} ";
}
}
FooDeserializer类
import java.io.IOException;
import com.fasterxml.jackson.core.JsonParser;
import com.fasterxml.jackson.core.JsonToken;
import com.fasterxml.jackson.databind.DeserializationContext;
import com.fasterxml.jackson.databind.JsonDeserializer;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.deser.ResolvableDeserializer;
import com.fasterxml.jackson.databind.deser.std.StdDeserializer;
import jackson.Outer.Foo;
public class FooDeserializer extends StdDeserializer<Outer.Foo> implements ResolvableDeserializer {
private static final long serialVersionUID = 1L;
private final JsonDeserializer<?> defaultDeserializer;
public FooDeserializer(JsonDeserializer<?> defaultDeserializer, Class<?> clazz) {
super(clazz);
this.defaultDeserializer = defaultDeserializer;
}
@Override
public Outer.Foo deserialize(JsonParser parser, DeserializationContext context) throws IOException {
if (parser.getCurrentToken() == JsonToken.VALUE_STRING) {
JsonNode node = parser.getCodec().readTree(parser);
if (node.isTextual()) {
return new Foo(node.asText(), null);
}
}
return (Foo) defaultDeserializer.deserialize(parser, context);
}
@Override
public void resolve(DeserializationContext ctxt) throws JsonMappingException {
((ResolvableDeserializer) defaultDeserializer).resolve(ctxt);
}
}
外部类
public class Outer {
private Foo foo;
public Foo getFoo() {
return foo;
}
public void setFoo(Foo foo) {
this.foo = foo;
}
public static class Foo {
private String bar;
private String name;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getBar() {
return bar;
}
public void setBar(String bar) {
this.bar = bar;
}
public Foo() {
}
public Foo(String name, String bar) {
this.name = name;
this.bar = bar;
}
}
}
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