This will do what you want with some caveats:
- It assumes there is a default constructor.
- It skips primitives.
- It skips already initialised objects.
- It will only initialize the packages specified (startsWith match) to avoid initializing other things like HashMaps etc that get very messy.
- It has only been tested with simple objects.
- You might not be able to access the fields if your have a security manager policy set.
- If there is any kind of recursive loop such as obj_A has a obj_B has a obj_A then it will fail with a stack overflow.
- It won't access and set values from superclasses (but could be made to).
I would ask if this is the best solution though as it would be prone to failure if things aren't quite as expected deep in the objects.
Initializer.java
import java.lang.reflect.Field;
import java.util.HashSet;
import java.util.Set;
import org.example.something.A;
public class Initilizer {
public static void initialize(Object object, Set<String> packages)
throws IllegalArgumentException,
IllegalAccessException {
Field[] fields = object.getClass().getDeclaredFields();
for (Field field : fields) {
String fieldName = field.getName();
Class<?> fieldClass = field.getType();
// skip primitives
if (fieldClass.isPrimitive()) {
System.out.println("Skipping primitive: " + fieldName);
continue;
}
// skip if not in packages
boolean inPackage = false;
for (String pack : packages) {
if (fieldClass.getPackage().getName().startsWith(pack)) {
inPackage = true;
}
}
if (!inPackage) {
System.out.println("Skipping package: "
+ fieldClass.getPackage().getName());
continue;
}
// allow access to private fields
boolean isAccessible = field.isAccessible();
field.setAccessible(true);
Object fieldValue = field.get(object);
if (fieldValue == null) {
System.out.println("Initializing: " + fieldName);
try {
field.set(object, fieldClass.newInstance());
} catch (IllegalArgumentException | IllegalAccessException
| InstantiationException e) {
System.err.println("Could not initialize "
+ fieldClass.getSimpleName());
}
} else {
System.out
.println("Field is already initialized: " + fieldName);
}
fieldValue = field.get(object);
// reset accessible
field.setAccessible(isAccessible);
// recursive call for sub-objects
initialize(fieldValue, packages);
}
}
public static void main(String[] args) throws Exception {
A a = new A();
// Packages to initialize
Set<String> packages = new HashSet<>();
packages.add("com.example");
packages.add("org.example");
initialize(a, packages);
}
}
A.java
package org.example.something;
import com.example.other.B;
public class A {
private int x;
private B b;
private B be = new B();
private C c;
}
B.java
package com.example.other;
public class B {
private boolean y;
private D d;
}
C.java
package org.example.something;
import java.util.HashMap;
public class C {
private HashMap doNotInit;
}
D.java
package com.example.other;
public class D {
private String s;
}
Output
Skipping primitive: x
Initializing: b
Skipping primitive: y
Initializing: d
Skipping package: java.lang
Field is already initialized: be
Skipping primitive: y
Initializing: d
Skipping package: java.lang
Initializing: c
Skipping package: java.util