Serializing generic java object to JSON using Jackson

Question

When i tried to convert the following class instance to JSON (using Jackson)

public class RPCRespond<Result> {      private int code;     private Result result;     private boolean success;     private String failureReason;      public RPCRespond() {         this.code = 0;         this.success = true;         this.result = null;     }      public RPCRespond(Result result) {         this.code = 0;         this.success = true;         this.result = result;     }      public RPCRespond(int code, String failureReason) {         this.code = code;         this.success = false;         this.failureReason = failureReason;     }      public RPCRespond(int code, String failureReason, Object... args) {         this.code = code;         this.success = false;         this.failureReason = String.format(failureReason, args);     }      public Result getResult() {         return result;     }       public void setSuccess(boolean success) {         this.success = success;     }      public String getFailureReason() {         return failureReason;     }      public void setFailureReason(String failureReason) {         this.failureReason = failureReason;     }      public int getCode() {         return code;     }      public boolean getSuccess() {         return success;     }      @Transient     public String getAsJSON() {          String json = "";          ObjectMapper mapper = new ObjectMapper();         json = mapper.writeValueAsString(this) ;           return json ;     }  } 

it get into infinite loop of:

  at sun.reflect.GeneratedMethodAccessor48.invoke(Unknown Source)    at  sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)     at java.lang.reflect.Method.invoke(Method.java:601)     at  org.codehaus.jackson.map.ser.BeanPropertyWriter.get(BeanPropertyWriter.java:483)     at  org.codehaus.jackson.map.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:418)     at  org.codehaus.jackson.map.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:150)     at  org.codehaus.jackson.map.ser.BeanSerializer.serialize(BeanSerializer.java:112)     at  org.codehaus.jackson.map.ser.StdSerializerProvider._serializeValue(StdSerializerProvider.java:610)     at  org.codehaus.jackson.map.ser.StdSerializerProvider.serializeValue(StdSerializerProvider.java:256)     at  org.codehaus.jackson.map.ObjectMapper._configAndWriteValue(ObjectMapper.java:2566)     at  org.codehaus.jackson.map.ObjectMapper.writeValueAsString(ObjectMapper.java:2088) 

The initiation of the RPCRespond is done by

User u = new User() ; u.setFirstName("aaaa") ; RPCRespond<User> result = new RPCRespond<User>(u) ;  result.setSuccess(true) ;  return result.getAsJSON() ; 

How can I convert RPCRespond to JSON?

Answer 1

By default Jackson will serialize via get methods. Once it hits the getAsJson method, poom, infinite loop. Mark it with the @JsonIgnore annotation.

@JsonIgnore public String getAsJSON() {     ObjectMapper mapper = new ObjectMapper();     return mapper.writeValueAsString(this) ;  } 

You can also configure Jackson to serialize based on properties only, which may eliminate the need for the @JsonIgnore, but that may or may not meet your needs.

I believe the latest Jackson allows the choice of using the Hibernate @Transient annotation, although I'm not sure how to configure it (recent change).