[英]Jackson deserialize map null values to empty string
I'm trying to find a global ObjectMapper
configuration (or any other customization) for all json Map<String, String>
to get deserialized into a map without null
values (there should be an empty String instead) 我正在尝试为所有json
Map<String, String>
找到一个全局ObjectMapper
配置(或任何其他自定义),以反序列化为没有null
值的映射(而应该有一个空String)
eg 例如
class MyClass {
Map<String, String> dict;
String str;
public MyClass() {
}
public MyClass(Map<String, String> dict, String str) {
this.dict = dict;
this.str = str;
}
public Map<String, String> getDict() {
return dict;
}
public String getStr() {
return str;
}
}
...
final Map<String, String> dict = new HashMap<>();
dict.put("k1", "v1");
dict.put("k2", null);
final MyClass myClass = new MyClass(dict);
final String valueAsString = objectMapper.writeValueAsString(myClass);
final MyClass deserialized = objectMapper.readValue(valueAsString, MyClass.class);
deserialized.getDict().get("k2"); // = "" (empty String)
deserialized.getStr(); // = null
I know I can do it per POJO by annotating my class with @JsonDeserialize(using = MyDeserializer.class)
but I want it to work for all maps. 我知道我可以通过
@JsonDeserialize(using = MyDeserializer.class)
注释我的类,从而实现每个POJO的功能,但我希望它适用于所有地图。
I've also tried to tweak this solution to work for deserialization, but it throws NullPointerException
我也曾尝试调整此解决方案以进行反序列化,但是会抛出
NullPointerException
update: the "null to empty" conversion needs to work only on maps (with string value). 更新:“从空到空”转换仅需要在具有字符串值的地图上起作用。 (see updated example above)
(请参见上面的更新示例)
Look it works for me: 看起来对我有用:
import java.io.IOException;
import java.util.HashMap;
import java.util.Map;
import org.junit.Test;
import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.databind.JsonSerializer;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializerProvider;
import com.fasterxml.jackson.databind.ser.DefaultSerializerProvider;
public class TestTest {
@Test
public void test_Map_null_EmptyString_() throws IOException {
ObjectMapper mapper = new ObjectMapper();
DefaultSerializerProvider sp = new DefaultSerializerProvider.Impl();
sp.setNullValueSerializer(new NullSerializer());
mapper.setSerializerProvider(sp);
final Map<String, String> dict = new HashMap<>();
dict.put("k1", "v1");
dict.put("k2", null);
final MyClass myClass = new MyClass(dict);
final String valueAsString = mapper.writeValueAsString(myClass);
System.out.println(valueAsString);
final MyClass deserialized = mapper.readValue(valueAsString, MyClass.class);
System.out.println(deserialized.getDict().get("k2")); // = "" (empty String)
}
public class NullSerializer extends JsonSerializer<Object> {
public void serialize(Object value, JsonGenerator jgen, SerializerProvider provider) throws IOException {
jgen.writeString("");
}
}
}
class MyClass {
Map<String, String> dict;
public MyClass() {
}
public MyClass(Map<String, String> dict) {
this.dict = dict;
}
public Map<String, String> getDict() {
return dict;
}
}
I ended up using DeserializerModifier technique as follows: 我最终使用了DeserializerModifier技术,如下所示:
static class MapCustomDeserializerModifier extends BeanDeserializerModifier {
@Override
public JsonDeserializer<?> modifyMapDeserializer(DeserializationConfig config, MapType type, BeanDescription beanDesc, JsonDeserializer<?> deserializer {
final JsonDeserializer<?> jsonDeserializer = super.modifyMapDeserializer(config, type, beanDesc, deserializer);
if (type.getKeyType().isTypeOrSubTypeOf(String.class) && type.getContentType().isTypeOrSubTypeOf(String.class)) {
return new MapCustomDeserializer();
}
return jsonDeserializer;
}
}
static class MapCustomDeserializer extends JsonDeserializer<Map<String, String>> {
@Override
public Map<String, String> deserialize(JsonParser jsonParser, DeserializationContext ctxt) throws IOException, JsonProcessingException {
final Map<String, String> map = jsonParser.readValueAs(Map.class);
if (map != null) {
map.replaceAll((key, value) -> Strings.nullToEmpty(value));
}
return map;
}
}
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