iterate to all List type property of my objects recursively

[Jay Richards]

Hi,

maybe some expert in reflection can help me with my problem.

i need a way to access a List property on my object, but this must also recursively parse any List property it may find on the List Object.

just a simple traversing with system.out will do. please help. thanks.

[Stan James]

Look into reflection, ie using the methods on the Class class. Look at the JavaDoc for Class getFields() and getDeclaredFields(). Many frameworks that convert objects to XML or move objects in and out of databases use these tricks to get and set fields. Take a shot at making them work from the doc and let us know how it goes!

[Jay Richards]

hi, just wanna share

listing the properties of a class and checking if its a list was easy

/**
 * Traverse recursively and extract the primary key(s) used for the given ConcurrentEntity object
 * @param object ConcurrentEntity object
 * @return
 */
public static List<ProcessUsage> getProcessUsage(ConcurrentEntity object,int level){
List<ProcessUsage> list = new ArrayList<ProcessUsage>();
Class clazz = object.getClass();
Field         ff[];
Method        mm[];
ProcessUsage pu = new ProcessUsage();
//make sure processName was set properly
object.initProcessName();
pu.setProcessName(object.getProcessName());
pu.setKey(object.getId());
pu.setLevel(level);
list.add(pu);
//ff = clazz.getDeclaredFields();
//for (int i = 0; i < ff.length; i++) {
//System.out.println(ff[i].getType().getName()+" "+ff[i].getName());
//}
//System.out.println();
mm = clazz.getDeclaredMethods();
for (int i = 0; i < mm.length; i++) {
String methodName = mm[i].getName();
String returnType = mm[i].getReturnType().getName();
//System.out.println(returnType + " " + methodName);
if(returnType.equals("java.util.List")){
Object ret = ReflectionUtils.invoke(object,methodName);
//System.out.println("ret:"+ret);
if(ret instanceof List){
List newlist = (List)ret;
for(int j=0;j<newlist.size();j++){
Object obj = newlist.get(j);
//System.out.println("newlist["+j+"]="+obj+"("+(obj instanceof ConcurrentEntity)+")");
if(obj instanceof ConcurrentEntity){
list.addAll(getProcessUsage((ConcurrentEntity)obj,level+1));
}//end of instanceOf ConcurrentEntity
}//end of for(j)
}//end of instanceOf List
}//end of returnType.equals("java.util.List")
}//end of for(i)
return list;
}

ReflectionUtils

/**
 * Invoke a method of an Object via its method name
 * @param objThe Object that has the method
 * @param methodNamemethodName to invoke
 */
public static Object invoke(Object obj,String methodName){
log.info("ReflectionUtils::execute()[1]");
log.debug("class:"+obj.getClass().toString());
log.debug("methodName:"+methodName);
Object ret=null;
try{
java.lang.reflect.Method m = obj.getClass().getMethod(methodName, null);
ret = m.invoke(obj,new Object[]{});
}catch(Exception e){
log.error("ReflectionUtils::execute("+methodName+")[1]-"+e.getMessage(),e);
//System.out.println("ReflectionUtils::execute("+methodName+")-"+e.getMessage());
//e.printStackTrace(System.err);
}
return ret;
}

just posted my code just in case someone needs a similar approach.

hth,