If it's reasonable to alter the original Map
data structure to be serialized to better represent the actual value wanted to be serialized, that's probably a decent approach, which would possibly reduce the amount of Jackson configuration necessary. For example, just remove the null
key entries, if possible, before calling Jackson. That said...
要禁止使用空值序列化Map
个条目,请执行以下操作:
Before Jackson 2.9个
您仍然可以使用WRITE_NULL_MAP_VALUES
,但请注意,它已移动到SerializationFeature
:
mapper.configure(SerializationFeature.WRITE_NULL_MAP_VALUES, false);
Since Jackson 2.9
The WRITE_NULL_MAP_VALUES
is deprecated, you can use the below equivalent:
mapper.setDefaultPropertyInclusion(
JsonInclude.Value.construct(Include.ALWAYS, Include.NON_NULL))
要禁止使用空值序列化属性,可以使用configure the ObjectMapper
directly或@JsonInclude
注释:
mapper.setSerializationInclusion(Include.NON_NULL);
or:
@JsonInclude(Include.NON_NULL)
class Foo
{
public String bar;
Foo(String bar)
{
this.bar = bar;
}
}
据我所知,要处理null Map
键,一些自定义序列化是必要的.
A simple approach to serialize null
keys as empty strings (including complete examples of the two previously mentioned configurations):
import java.io.IOException;
import java.util.HashMap;
import java.util.Map;
import com.fasterxml.jackson.annotation.JsonInclude.Include;
import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.JsonSerializer;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializationFeature;
import com.fasterxml.jackson.databind.SerializerProvider;
public class JacksonFoo
{
public static void main(String[] args) throws Exception
{
Map<String, Foo> foos = new HashMap<String, Foo>();
foos.put("foo1", new Foo("foo1"));
foos.put("foo2", new Foo(null));
foos.put("foo3", null);
foos.put(null, new Foo("foo4"));
// System.out.println(new ObjectMapper().writeValueAsString(foos));
// Exception: Null key for a Map not allowed in JSON (use a converting NullKeySerializer?)
ObjectMapper mapper = new ObjectMapper();
mapper.configure(SerializationFeature.WRITE_NULL_MAP_VALUES, false);
mapper.setSerializationInclusion(Include.NON_NULL);
mapper.getSerializerProvider().setNullKeySerializer(new MyNullKeySerializer());
System.out.println(mapper.writeValueAsString(foos));
// output:
// {"":{"bar":"foo4"},"foo2":{},"foo1":{"bar":"foo1"}}
}
}
class MyNullKeySerializer extends JsonSerializer<Object>
{
@Override
public void serialize(Object nullKey, JsonGenerator jsonGenerator, SerializerProvider unused)
throws IOException, JsonProcessingException
{
jsonGenerator.writeFieldName("");
}
}
class Foo
{
public String bar;
Foo(String bar)
{
this.bar = bar;
}
}
要禁止使用null
个键序列化Map
个条目,需要进行进一步的自定义序列化处理.