如何在Java中使用Jackson库实现自定义序列化器？

public abstract void serialize(T value, JsonGenerator gen, SerializerProvider provider) throws IOException

import java.io.*;
import com.fasterxml.jackson.core.*;
import com.fasterxml.jackson.databind.*;
import com.fasterxml.jackson.databind.module.*;
import com.fasterxml.jackson.databind.ser.std.StdSerializer;
public class JacksonSerializeTest {
   public static void main(String[] args) throws Exception {
      JacksonSerializeTest test = new JacksonSerializeTest();
      test.serialize();
   }
   public void serialize() throws Exception {
      User user = new User();
      user.setFirstName("Raja");
      user.setLastName("Ramesh");
      ObjectMapper mapper = new ObjectMapper();
      SimpleModule module = new SimpleModule();
      module.addSerializer(User.class, new UserSerializer());
      mapper.registerModule(module);

      String jsonStr = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(user); // pretty print
      System.out.println(jsonStr);
   }
}
// User class
class User implements Serializable {
   private String firstName;
   private String lastName;
   public String getFirstName() {
      return firstName;
   }
   public void setFirstName(String firstName) {
      this.firstName = firstName;
   }
   public String getLastName() {
      return lastName;
   }
   public void setLastName(String lastName) {
      this.lastName = lastName;
   }
}
// UserSerializer class
class UserSerializer extends StdSerializer<User> {
   public UserSerializer() {
      this(null);
   }
   public UserSerializer(Class<User> t) {
      super(t);
   }
<strong>   </strong>@Override
   public void serialize(User value, JsonGenerator jgen, SerializerProvider provider) throws       IOException, JsonProcessingException {
      jgen.writeStartObject();
      jgen.writeStringField("firstName", value.getFirstName());
      jgen.writeStringField("lastName", value.getLastName());
      jgen.writeEndObject();
   }
}

{
 "firstName" : "Raja",
 "lastName" : "Ramesh"
}