Read and write Json properties using methods (ie. getters & setters)

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if your object has an int getId(); method. Maybe you want to have a 

@Field("id")
public int getId();

When the Json is generated the getId() method is called and the result is 
placed in "id"
I know that I could have a int field in my class, but, in my case the Id is 
generate by Hibernate once the object is saved.

Original issue reported on code.google.com by Germanattanasio on 7 Sep 2010 at 2:04

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This will be extremely useful for synthetic fields and for type hierarchies. 
I.e. say you have a base class with an Id field that you want to serialize with 
a type specific name. You could have the Id be transient and have a getId 
method that child classes could override to return their Id types etc.

Original comment by nfiedel on 17 Sep 2010 at 5:58

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Original comment by limpbizkit on 6 Oct 2010 at 5:38

• Added labels: Type-Enhancement
• Removed labels: Type-Defect

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Issue 185 has been merged into this issue.

Original comment by limpbizkit on 6 Oct 2010 at 6:09

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Original comment by limpbizkit on 6 Oct 2010 at 6:10

• Changed title: Read and write Json properties using methods (ie. getters & setters)

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Original comment by inder123 on 3 Nov 2010 at 12:25

• Added labels: Milestone-Undefined

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It would be nice if GSON used getters and setters, actually it is a bit 
confusing to use as one cannot transform data in setters.

Original comment by astronau...@gmail.com on 25 May 2011 at 9:36

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Hi! Actually it is not very hard to check out sources of GSON and add "use 
getters" ability. I required this in order to be able to work with Hibernate 
proxies seamlessly ... if anybody is interested, mail me to 
jakub.gemrot@gmail.com (I'm sorry I don't have time to create patches right 
now...).

The key place to patch is JsonSerializationVisitor.visitFieldUsingCustomHandler(
      FieldAttributes f, Type declaredTypeOfField, Object parent)

Look for:

      obj = f.get(parent);

Than just replace with:

      Object obj = null;
      if (useGetters) {
          String fieldName = f.getName();
          if (fieldName == null || fieldName.length() == 0) throw new RuntimeException("fieldName is invalid!");
          String getter = null;
          if (declaredTypeOfField == boolean.class) {
              getter = "is";
          } else
          if (declaredTypeOfField == Boolean.class) {
              getter = "get"; // should be get... but some frameworks will put "is" ... checked later if this is not found...
          } else {
              getter = "get";
          }
          getter += fieldName.substring(0, 1).toUpperCase() + (fieldName.length() <= 1 ? "" : fieldName.substring(1));
          Method method = null;
          try {
              method = parent.getClass().getMethod(getter);
          } catch (Exception e) {
              // no getter present
              if (declaredTypeOfField == Boolean.class) {
                  // getter might start with "get" not "is"
                  getter = "is" + fieldName.substring(0, 1).toUpperCase() + (fieldName.length() <= 1 ? "" : fieldName.substring(1));
                  try {
                      method = parent.getClass().getMethod(getter);
                  } catch (Exception e2) {
                    // no, event "is" prefixed getter for Boolean.class does not exist
                  }
              }
          }
          if (method == null) {
              obj = f.get(parent);
          } else {
              try {               
                obj = method.invoke(parent);
            } catch (Exception e) {             
                throw new RuntimeException("Could not invoke getter: " + obj.getClass() + "." + getter + "() !", e);
            }  
          }              
      } else {      
          obj = f.get(parent);
      }

See how boolean.class & Boolean.class are handled, I know it looks wierd. The 
trick is that you have to take care of boolean.class as well as Boolean.class. 
Eclipse is suggesting that "Boolean" bean properties should use getters 
prefixed with "get" but Hibernate is using "is". So that case must be treated 
extra.

Cheers!

Jimmy

Original comment by Jakub.Ge...@gmail.com on 18 Jun 2011 at 3:38

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Oh, and watch out for failing tests inside DefaultTypeAdaptersTest working with 
Date/Timestamp/etc... just comment them out :)

Best, Jimmy

Original comment by Jakub.Ge...@gmail.com on 18 Jun 2011 at 3:38

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If you wish to test your code after that, you may use this (it's not actually a 
test case ... but it will print serialized Gson that will contain different 
values than actually stored due to the getter definition):

  public static class MyUtilClass {

      private int util = 5;

      public MyUtilClass() {

      }

      public MyUtilClass(int util) {
          this.util = util;
      }

    public int getUtil() {
        return util * 10;
    }

    public void setUtil(int util) {
        this.util = util * 10;
    }

  }

  public static class MyClass {

      private int value = 10;

      private MyUtilClass cls = new MyUtilClass();

      private MyUtilClass[] clss = new MyUtilClass[3];

      private List<MyUtilClass> list = new ArrayList<MyUtilClass>(10);

      private Map<Integer, MyUtilClass> map = new HashMap<Integer, MyUtilClass>();

      private Set<MyUtilClass> set = new HashSet<MyUtilClass>();

      private Boolean b1 = true;

      private boolean b2 = true;

      public MyClass() {
          clss[0] = new MyUtilClass(1);
          clss[2] = new MyUtilClass(2);
          list.add(new MyUtilClass(3));
          list.add(new MyUtilClass(4));
          map.put(1, new MyUtilClass(5));
          map.put(2, new MyUtilClass(6));
          set.add(new MyUtilClass(7));
          set.add(new MyUtilClass(8));
      }

      public int getValue() {
          return value * 10;
      }

      public void setValue(int value) {
          this.value = value * 100;
      }

    public Boolean isB1() {
        return false;
    }

    public boolean isB2() {
        return false;
    }

  }

  public void testClassSerialization() {
      GsonBuilder builder = new GsonBuilder();
      builder.setUseGetters(true);
      builder.setPrettyPrinting();
      gson = builder.create();    
      MyClass obj = new MyClass();
      String json = gson.toJson(obj);
      System.out.println(json);
  }

Best,
Jimmy

Original comment by Jakub.Ge...@gmail.com on 18 Jun 2011 at 3:42

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In Gson 2.1, it's possible to do this as an extension with a TypeAdapterFactory 
based on ReflectiveTypeAdapterFactory. We may want to provide an extension.

Original comment by limpbizkit on 29 Dec 2011 at 5:36

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Issue 285 has been merged into this issue.

Original comment by limpbizkit on 29 Dec 2011 at 5:52

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I think this implementation is good, except I suggest make configurable to 
throw an exception or not. If getter is not found, it maybe treated as this 
field is not exposed. This is the common case, why getter/setter not provided 
for a field.

Second thing: I should swap the two process way of Boolean class, i think "is" 
prefix is more common than "get" for these fields.

Original comment by h...@hron.me on 11 Mar 2012 at 3:54

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I made a small code to support bind by getter/setter method or field.
Here is the sample code:

        GsonBuilder bsonBuilder = new GsonBuilder();
        Gson gson = bsonBuilder.setFieldBindingStrategy(FieldBindingStrategy.GET_METHOD).create();
        // or by field modifier: gson = bsonBuilder.setFieldBindingStrategy(FieldBindingStrategy.FieldModifier.valueOf(Modifier.PRIVATE+Modifier.PROTECTED)).create();

Original comment by 70l...@gmail.com on 21 Feb 2014 at 7:27

Attachments:

• gson-2.3.jar
• gson-2.3-sources.jar

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one more suggestion: comparing to fastJson or jackson, the performance is a bit 
slower. I think performance of gson should be improved continually.

Original comment by 70l...@gmail.com on 21 Feb 2014 at 7:30