Java toString() using reflection?

Solution 1:

Apache commons-lang ReflectionToStringBuilder does this for you.

import org.apache.commons.lang3.builder.ReflectionToStringBuilder

// your code goes here

public String toString() {
   return ReflectionToStringBuilder.toString(this);
}

Solution 2:

Another option, if you are ok with JSON, is Google's GSON library.

public String toString() {
    return new GsonBuilder().setPrettyPrinting().create().toJson(this);
}

It's going to do the reflection for you. This produces a nice, easy to read JSON file. Easy-to-read being relative, non tech folks might find the JSON intimidating.

You could make the GSONBuilder a member variable too, if you don't want to new it up every time.

If you have data that can't be printed (like a stream) or data you just don't want to print, you can just add @Expose tags to the attributes you want to print and then use the following line.

 new GsonBuilder()
.setPrettyPrinting()
.excludeFieldsWithoutExposeAnnotation()
.create()
.toJson(this);

Solution 3:

W/reflection, as I hadn't been aware of the apache library:

(be aware that if you do this you'll probably need to deal with subobjects and make sure they print properly - in particular, arrays won't show you anything useful)

@Override
public String toString()
{
    StringBuilder b = new StringBuilder("[");
    for (Field f : getClass().getFields())
    {
        if (!isStaticField(f))
        {
            try
            {
                b.append(f.getName() + "=" + f.get(this) + " ");
            } catch (IllegalAccessException e)
            {
                // pass, don't print
            }
        }
    }
    b.append(']');
    return b.toString();
}


private boolean isStaticField(Field f)
{
    return Modifier.isStatic(f.getModifiers());
}

Solution 4:

If you're using Eclipse, you may also have a look at JUtils toString generator, which does it statically (generating the method in your source code).

Solution 5:

Not reflection, but I had a look at generating the toString method (along with equals/hashCode) as a post-compilation step using bytecode manipulation. Results were mixed.