Instantiate an object graph from a property file

PropsInstantiator.java

import java.io.BufferedReader;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.HashMap;
import java.util.Map;

public class PropsInstantiator {

	private static Object getProperty(Object target, String propName) throws Exception {
		for(Method m : target.getClass().getMethods()) {
			String name = m.getName();
			
			if(!name.startsWith("get") || m.getParameterTypes().length != 0)
				continue;
			
			name = name.substring(3);
			if(name.equalsIgnoreCase(propName)) {
				return m.invoke(target);
			}
		}
		
		for(Field f : target.getClass().getFields()) {
			String name = f.getName();
			
			if(name.equalsIgnoreCase(propName)) {
				return f.get(target);
			}
		}
		return null;
	}
	
	private static abstract class SettableProperty {
		public final String name;
		public final Class<?> type;
		public abstract void set(Object o) throws Exception;
		
		public SettableProperty(String name, Class<?> type) {
			this.name = name;
			this.type = type;
		}
		
		public static SettableProperty getSettable(final Object target, String propName) {
			for(Method m : target.getClass().getMethods()) {
				String name = m.getName();
				
				if(!name.startsWith("set") || m.getParameterTypes().length != 1)
					continue;
				
				name = name.substring(3);
				if(name.equalsIgnoreCase(propName)) {
					final Method myM = m;
					return new SettableProperty(propName, m.getParameterTypes()[0]) {
						public void set(Object o) throws IllegalAccessException, IllegalArgumentException, InvocationTargetException {
							myM.invoke(target, o);
						}
					};
				}
			}
			
			for(Field f : target.getClass().getFields()) {
				String name = f.getName();
				
				if(name.equalsIgnoreCase(propName)) {
					final Field myF = f;
					return new SettableProperty(propName, f.getType()) {
						public void set(Object o) throws IllegalArgumentException, IllegalAccessException {
							myF.set(target, o);
						}
					};
				}
			}
			return null;
		}
	}
	
	private static Object parseEnum(Class<?> enumType, String str) {
		if(!str.contains(".")) {
			// Single enum
			for(Object o : enumType.getEnumConstants()) {
				Enum e = (Enum) o;
				if(e.name().equals(str))
					return e;
			}
		}
		return null;
	}
	
	private static Object parseObjectReference(Object t, String path) throws Exception {
		if(path.startsWith("@")) {
			// Reference from root object
			path = path.substring(1);
			String[] parts = path.split("\\.");
			for(int i = 0; i < parts.length && t != null; i++) {
				t = getProperty(t, parts[i]);
			}
			return t;
		} else if(path.startsWith("!")){
			// New object
			path = path.substring(1);
			return Class.forName(path).newInstance();
		}
		
		return null;
	}
	
	public static void parse(InputStream is, Object target) throws Exception {
		
		try(BufferedReader br = new BufferedReader(new InputStreamReader(is))) {
			
			String line = null;
			while((line = br.readLine()) != null) {
				if(line.isEmpty())
					continue;
				
				if(line.startsWith("#"))
					continue;

				String key = line.replaceFirst(" *=.*","");
				String valueString = line.replaceFirst(".*= *","");
				
				String[] keyParts = key.split("\\.");
				
				Object t = target;
				
				for(int i = 0; i < keyParts.length-1 && t != null; i++) {
					t = getProperty(t, keyParts[i]);
				}

				
				SettableProperty s = SettableProperty.getSettable(t, keyParts[keyParts.length-1]);
				
				Object refObj = parseObjectReference(target, valueString);
				if(refObj != null) {
					s.set(refObj);
				} else if(s.type.isEnum()) {
					s.set(parseEnum(s.type, valueString));
				} else if(s.type == String.class) {
					s.set(valueString);
				} else if(s.type == Integer.class) {
					s.set(Integer.parseInt(valueString));
				} else if(s.type == Double.class) {
					s.set(Double.parseDouble(valueString));
				} else if(s.type == Float.class) {
					s.set(Float.parseFloat(valueString));
				}
				
			}
		}
		
		
	}
}

Test.java

class Test {
	
	public static enum State {
		RUNNING,
		STOPPED;
	}

	private State state;
	
	
	public Object child = null;
	
	private String description = null;
	
	public void setDescription(String description) {
		this.description = description;
	}
	
	public void setState(State state) {
		this.state = state;
	}
	
	public State getState() {
		return this.state;
	}
	
	
	public static void main(String[] args) throws Exception {
		
		Test t = new Test();
		
		PropsInstantiator.parse(Test.class.getResourceAsStream("/test.properties"), t);
		
	}
		
}

test.properties

# Set a String setter
description=Hello There

# Set a field with a new object
child=!Test

# Set a String setter
child.description=I am the child thing

# Set an Enum setter
child.state=RUNNING

# Set an Enum setter with an object from elsewhere
[email protected]

# Set a field with a new object
child.child=!java.lang.String