java toString for any object [duplicate]

Answer 1

There are few ways to implement toString method.

1. Reflections (Apache library)

   @Override
   public String toString(){
       return org.apache.commons.lang3.builder.ReflectionToStringBuilder.toString(this);
   }
   

2. JSON based implementation (GSON, Jackson libraries)

   // GSON library for JSON
   @Override
   public String toString(){
       return new com.google.gson.Gson().toJson(this);
   }
   
   // Jackson libabry for JSON/YAML
   @Override
   public String toString() {
       try {
           return new com.fasterxml.jackson.databind.ObjectMapper().writerWithDefaultPrettyPrinter().writeValueAsString(this);
       } catch (com.fasterxml.jackson.core.JsonProcessingException e) {
           e.printStackTrace();
       }
       return null;
   }
   

3. ToStringBuilder (available with apache-commons library)

   @Override
   public String toString() {
       return new org.apache.commons.lang3.builder.ToStringBuilder(this).
           append("field1", field1).
           append("field2", field2).
           toString();
   }
   

4. Hard-core toString() implementation

   @Override
   public String toString() {
       return new StringBuilder()
           .append("field1:"+field1)
           .append("field2:"+field2)
           .toString();
   }
   

Answer 2

If you hava a lot of objects then instead of adding toString in every class use code instrumentation (you can alter .class in jars or change them at loadtime using javaagent). For example AspectJ would help, but there are lots other alternatives. For example you can do such a thing (using AspectJ and ToStringBuilder from Apache Commons):

@Aspect
public class ToStringAspect {

     @Around("execution(String *.toString()) &&  target(t) && within(your.target.package.*)")
     public String toStringCall(Object t) {
        return ToStringBuilder.reflectionToString(t);
    }
}

ToStringBuilder is very flexible. e.g. if you don't need class name use style by setting StandardToStringStyle#setUseClassName(false):

 public String toStringCall(Object t) {
     StandardToStringStyle style = new StandardToStringStyle();
     style.setUseClassName(false);
     style.setUseIdentityHashCode(false);
    ToStringBuilder builder = new ReflectionToStringBuilder(t, style);
    return builder.toString();
}