[Java] 動態修改目標Class 的 private 屬性－Lung-Yu,Tsai 的部落格

一般情況下物件屬性的存取只能操作公開(public)的方法或屬性，有時候有某些情況需要操作被設計為private 的方法或屬性的時候可以透過反射機制進行。

以下將利用反射機制，來修改與設定目標物件的屬性。

首先先製作一個類別

public class Student {
	private int id;
	private String name;
	private boolean male;
	private double account;
	public int getId() {
		return id;
	}
	public void setId(int id) {
		this.id = id;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public boolean isMale() {
		return male;
	}
	public void setMale(boolean male) {
		this.male = male;
	}
	public double getAccount() {
		return account;
	}
	public void setAccount(double account) {
		this.account = account;
	}
}

以下程式會透過反射機制對資料進行修改，首先先取得目標的反射物件，透過setAccessible將該屬性的權限改為可修改，並利用set方法給予值，實作程式碼如下:

public class Test {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Student student = new Student();
		Class<?> clazz = student.getClass();
		
		try {
			Field id = clazz.getDeclaredField("id");
			System.out.println("設定前的 id = " + student.getId());
			id.setAccessible(true);
			id.setInt(student, 10);
			System.out.println("設定後的 id = " + student.getId());
			System.out.println();
			
			Field name = clazz.getDeclaredField("name");
			System.out.println("設定前的 name = " + student.getName());
			name.setAccessible(true);
			name.set(student, "haha");
			System.out.println("設定後的 name = " + student.getName());
			System.out.println();
			
			Field male = clazz.getDeclaredField("male");
			System.out.println("設定前的 male = " + student.isMale());
			male.setAccessible(true);
			male.setBoolean(student, true);
			System.out.println("設定後的 male = " + student.isMale());
			System.out.println();
			
			Field account = clazz.getDeclaredField("account");
			System.out.println("設定前的 account = " + student.getAccount());
			account.setAccessible(true);
			account.setDouble(student, 148.24);
			System.out.println("設定後的 account = " + student.getAccount());
			System.out.println();
		} catch (NoSuchFieldException | SecurityException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (IllegalArgumentException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (IllegalAccessException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}		
	}

}