模擬jvm類雙親委託加載機制

jdk源代碼，以及流程圖以下

模擬代碼

package test.com.shareinfo.app;

public abstract class AbstrFather {
	public AbstrFather parent;

	protected String loadClass(String str) throws Exception {
		String var4 = null;
		try {
			if (this.parent != null) {
				System.out.println(this.getClass() + " 擁有父加載器，移交給" + this.parent.getClass() + "加載");
				var4 = this.parent.loadClass(str);
			} else {
				var4 = this.findBootstrapClassOrNull(str);
			}
		} catch (Exception var10) {
			System.out.println(var10.getMessage());
			;

		}

		if (var4 == null) {
			var4 = this.findClass(str);
		}
		return var4;
	}


	protected abstract String findClass(String str) throws Exception;

	public String findBootstrapClassOrNull(String str) throws Exception {
		throw new Exception(this.getClass() + " find class error");
	}

	public AbstrFather getParent() {
		return parent;
	}

	public void setParent(AbstrFather parent) {
		this.parent = parent;
	}

}

 

三個加載類的代碼

public class BootClass extends AbstrFather {

	@Override
	protected String findClass(String str) throws Exception {
		throw new Exception(this.getClass() + "  findClass error");
	}

}



public class ExtClass extends AbstrFather {

	@Override
	protected String findClass(String str) throws Exception {
		throw new Exception(this.getClass() + "  findClass error");
	}

}


public class AppClass extends AbstrFather {

	@Override
	protected String findClass(String str) throws Exception {
		System.out.println(this.getClass() + "  findClass success");
		return "myload";
	}

}

 測試代碼

public class LoadTest {
 
	public static void main(String[] args) throws ClassNotFoundException {

		AbstrFather my = new AppClass();
		BootClass bc = new BootClass();
		ExtClass ec = new ExtClass();
		ec.setParent(bc);
		my.setParent(ec);
		try {
			my.loadClass("1");
		} catch (Exception e) {

			e.printStackTrace();
		}

	}

}

結果打印

class test.com.shareinfo.app.AppClass 擁有父加載器，移交給class test.com.shareinfo.app.ExtClass加載
class test.com.shareinfo.app.ExtClass 擁有父加載器，移交給class test.com.shareinfo.app.BootClass加載
class test.com.shareinfo.app.BootClassbootStrp find class error
class test.com.shareinfo.app.BootClass  findClass error
class test.com.shareinfo.app.ExtClass  findClass error
class test.com.shareinfo.app.AppClass  findClass success