понедельник, 6 октября 2008 г.

Using reflections for test equals.

Problem: test for equals two objects of the same class by all fields(deep equals).
For solve this problem I use reflection API from JDK. Package that store classes for reflection is java.lang.reflect. I wrote simple helper class with static methods.

You can find the complete realization at the and of the post.

First of all we should describe algorithm:
Input: two object that we need compare.
Steps:
1. Check objects references
obj1 == obj2

2.Check that names of classes for this objects are identically
c1.getName().compareTo(c2.getName()) == 0

3.While class is not java.lang.Object do steps from 4 to 8
while (!c1.getName().equals(Object.class.getName()))  {...}

4.Go through all fields in class

for (Field f1 : c1.getDeclaredFields())

5.Ignore inner classes, because they have cross references and we have infinity loop.
if (!f1.getName().contains("this$")) {...}

6.Get the same field from second class.
Field f2 = c2.getDeclaredField(f1.getName());

7.Turn off access checking(we want equals all:))
f1.setAccessible(true);
f2.setAccessible(true);

8.Call method that do test objects of these fields and if its result is fail return false.
if (!doObjectEquals(f1.get(obj1), f2.get(obj2))) {
    return false;
}

9.When process all fields, get the super classes of our objects, cast objects to superclass and go to step 4.
c1 = c1.getSuperclass();
c2 = c2.getSuperclass();
obj1 = c1.cast(obj1);
obj2 = c2.cast(obj2);

Now, we can write method that will be equals two objects. First of all, we should check this objects for nulls. If both objects are null, then we do nothing and return true. If one of this object is null...then we do nothing, too :), but return false. For equals two objects, we should try to find declared method equals(). If the object have this method, then we call it and return it's result, else we should recursively call first method for equals each field in this object. Also in this method we should process arrays and collections. In Java, Collections API have three kind of objects. There are Set, List and Map.  In Map we can compare Set of Map.Entry objects, that returns method Map.entrySet(). Notice, that these methods compare items in array without order.

I write some static helpers for equals collections using reflections.

Also, we should specially equals  fields of enum types.  We can check field using method Field.isEnumConstant(). If field is enum constant, we should simple equals() values .

Finally, helper class looks like this:
import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.util.*;

/**
 * @author : Pokidov.Dmitry
 * @date: 27.05.2008
 * 

* Class that help to test equals for two object. * For test use {@code weakEquals()} method. */ public class WeakEqualsHelper { private static ArrayList<String> errorLog = new ArrayList<String>(); private static Map<String, List<String>> fields; private enum CheckNullsResult { BOTH_NULLS, NOT_NULLS, ONE_NULL; } /** * Recursively compare object by its class and all superclasses. * To standalone test collections, arrays and maps use methods: * {@code equalsCollection(), equalsArray(), equalsMap()} * * @param o1 First object for compare * @param o2 Second object for compare * @return {@code true}, if objects are equals, else {@code false} */ public static boolean weakEquals(Object o1, Object o2) { return weakEquals(o1, o2, null); } /** * Recursively compare object by its class and all superclasses. * To standalone test collections, arrays and maps use methods: * {@code equalsCollection(), equalsArray(), equalsMap()} * * @param o1 First object for compare * @param o2 Second object for compare * @param notEqualsFields fields that will be ignore. Key is name of class, Value - list of field's name. * @return {@code true}, if objects are equals, else {@code false} */ public static boolean weakEquals(Object o1, Object o2, Map<String, List<String>> notEqualsFields) { fields = notEqualsFields; boolean ret = doEquals(o1, o2); if (!ret) { for (String error : errorLog) { System.out.println(error); } } return ret; } public boolean weakEquals(Object o) { if (o == null || !(o instanceof WeakEqualsHelper)) { return false; } return o == this || doEquals(this, o); } private static boolean needEqual(Field f, Map<String, List<String>> fields) { if (fields != null) { List<String> classFields = fields.get(f.getDeclaringClass().getName()); return !(classFields != null && classFields.contains(f.getName())); } return true; } public static boolean doEquals(Object obj1, Object obj2) { if (obj1 == obj2) { return true; } Class c1 = obj1.getClass(); Class c2 = obj2.getClass(); if (c1.getName().compareTo(c2.getName()) == 0) { while (!c1.getName().equals(Object.class.getName())) { for (Field f1 : c1.getDeclaredFields()) { if (needEqual(f1, fields)) { String errorMessage = "ERROR: Class " + obj1.getClass().getName() + " are not equal in field -->" + f1.getName() + "<--"; if (!f1.getName().contains("this$")) { try { Field f2 = c2.getDeclaredField(f1.getName()); f1.setAccessible(true); f2.setAccessible(true); errorLog.add("Current field-->" + f1.getName() + "<--"); if (f1.isEnumConstant()) { if (!f1.get(obj1).equals(f2.get(obj2))) { return false; } } else if (!doObjectEquals(f1.get(obj1), f2.get(obj2))) { errorLog.add(errorMessage + "[" + (f1.get(obj1) != null && f1.get(obj1).equals("null") ? "NULL" : f1.get(obj1)) + ":" + (f2.get(obj2) != null && f2.get(obj2).equals("null") ? "NULL" : f2.get(obj2)) + "]"); return false; } } catch (NoSuchFieldException nsme) { errorLog.add("ERROR: No such field " + f1.getName()); return false; } catch (IllegalAccessException e) { e.printStackTrace(); return false; } } else { errorLog.add("INFO: ignore field -->" + f1.getName() + "<--"); } } else { System.out.println("INFO: ignore field -->" + f1.getName() + "<--"); } } c1 = c1.getSuperclass(); c2 = c2.getSuperclass(); obj1 = c1.cast(obj1); obj2 = c2.cast(obj2); } } else { errorLog.add("Class names are not equals in field[" + c1.getName() + "," + c2.getName() + "]"); return false; } return true; } private static boolean doObjectEquals(Object o1, Object o2) { if (checkNulls(o1, o2) == CheckNullsResult.NOT_NULLS) { if (o1 instanceof Map.Entry) { Map.Entry e1 = (Map.Entry) o1; Map.Entry e2 = (Map.Entry) o2; return doObjectEquals(e1.getKey(), e2.getKey()) && doObjectEquals(e1.getValue(), e2.getValue()); } else if (o1 instanceof Map) { return equalsMap((Map) o1, (Map) o2); } else if (o1 instanceof Collection) { return equalsCollection((Collection) o1, (Collection) o2); } else if (o1.getClass().isArray()) { return equalsArray((Object[]) o1, (Object[]) o2); } else if (!o1.getClass().getName().equals(Object.class.getName())) { if (hasEquals(o1.getClass())) { if (!o1.equals(o2)) { if (o1 instanceof String && o2 instanceof String) { String s1 = ((String) o1).replaceAll("[\n\t\r ]", ""); String s2 = ((String) o2).replaceAll("[\n\t\r ]", ""); if (!s1.equals(s2)) { return false; } else { System.out.println("WARNING: Strings are not equals with escape symbols and whitespaces"); return true; } } System.out.println("Equals return false"); return false; } return true; } else { return doEquals(o1, o2); } } System.out.println("UNKNOWN TYPE: " + o1.getClass().getName()); } return equalsForNull(o1, o2); } private static CheckNullsResult checkNulls(Object object, Object otherObject) { if (object == null && otherObject == null) { return CheckNullsResult.BOTH_NULLS; } if (object != null && otherObject != null) { return CheckNullsResult.NOT_NULLS; } return CheckNullsResult.ONE_NULL; } private static boolean equalsForNull(Object object, Object otherObject) { return object == null && otherObject == null; } public static boolean equalsMap(Map map, Map otherMap) throws NullPointerException { return equalsCollection(map.entrySet(), otherMap.entrySet()); } public static boolean equalsCollection(Collection collection, Collection otherCollection) throws NullPointerException { return equalsArray(collection.toArray(), otherCollection.toArray()); } public static boolean equalsArray(Object[] array, Object[] otherArray) throws NullPointerException { if (array.length != otherArray.length) { errorLog.add("Array or Collection length are not equals[" + array.length + "," + otherArray.length + "]"); return false; } ArrayList<Integer> usedIndexes = new ArrayList<Integer>(); for (int i = 0; i < array.length; i++) { Object currObject = array[i]; boolean found = false; for (int k = 0; k < otherArray.length; k++) { if (!usedIndexes.contains(k)) { found = doObjectEquals(currObject, otherArray[k]); if (found) { usedIndexes.add(k); break; } } } if (!found) { return false; } } return true; } private static boolean hasEquals(Class c) { Method[] methods = c.getDeclaredMethods(); for (Method m : methods) { if (m.getName().equals("equals") && m.getParameterTypes().length == 1) { return true; } } return false; } /*------------TEST------------*/ public class TestClass { public class TestNestClass extends TestClass { public TestNestClass(int a, int b, ArrayList list) { super(a, b, list); } public void setD(int d) { this.d = d; } public void putMap(String s, Integer i) { map.put(s, i); } private int d; private Map<String, Integer> map = new HashMap<String, Integer>(); } private int a; private int b; private ArrayList list = new ArrayList(); private String c = "Hello!!!"; public TestClass(int a, int b, ArrayList list) { this.a = a; this.b = b; this.list = list; } public int getA() { return a; } public int getB() { return b; } public String getC() { return c; } public void setC(String c) { this.c = c; } public ArrayList getList() { return list; } public TestNestClass createNest() { return new TestNestClass(a, b, list); } } public TestClass createTestClass(int a, int b, ArrayList list) { return new TestClass(a, b, list); } public static void main(String[] args) { ArrayList ar1 = new ArrayList(); ar1.add(1); ar1.add(5); ar1.add(7); ArrayList ar2 = new ArrayList(); ar2.add(1); ar2.add(5); ar2.add(7); WeakEqualsHelper eh = new WeakEqualsHelper(); TestClass tc1 = eh.createTestClass(1, 15, ar1); TestClass tc2 = eh.createTestClass(1, 15, ar2); TestClass.TestNestClass tnc = tc1.createNest(); TestClass.TestNestClass tnc2 = tc2.createNest(); tnc.putMap("Hello", 1); tnc2.putMap("Hello", 1); tnc.putMap("goodbye", 1); tnc2.putMap("goodbye", 1); System.out.println("tc1.equals(tc2) == " + WeakEqualsHelper.doEquals(tnc, tnc2)); } }


I add some features in this implementation:
-I can pass Map<string, List<String>> that contains class name as key and list of fields name that will be ignored when equals
-If string are not equals, then its will be equals igonring escape symbols and whitespaces.
-I add simple test.

Usage: I use this class in unit testing when migrate from digester to castor. We need serialization of objects.
I rewrite over 1MB of mappings. I was in hell :)

UPD: do formatting, now you can simple copy class and use it.

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