今天想寫個隨筆，最近經常遇到使用junit的時候報java.lang.NoClassDefFoundError，今天算是恍然大悟了，原來junit雖然在gradle裏面配置了，也在Project and External Dependencies中看到了junit的jar包，並能在這個junit的jar包裏面找到org/junit/runner/manipulation/Filter這個類，但是run as junit test的時候就偏偏要報java.lang.NoClassDefFoundError: org/junit/runner/manipulation/Filter。

　　以為是gradle配置問題，testImplementation、implementation、api都不行　　

　　後來想想，出現這種情況無外乎gradle中引入的jar包（即Project and External Dependencies中的jar包）在run as junit test的時候並沒有被jvm加載，所以才會出現這種現象，解決辦法就是在build path 中add library，加入junit

　　下面附上在main裏面打出已加載的class：

package proxy;

import java.lang.reflect.Field;
import java.lang.reflect.Proxy;
import java.util.Vector;

import org.junit.Test;

/**
* Created by [email protected] on 2018年6月9日.
*/

public class TestProxy {

	@Test
	public void test1() {
		
		TestLog testLog = new TestLogImpl();
		TestLogInterceptor testLogInterceptor = new TestLogInterceptor();
		testLogInterceptor.setTarget(testLog);
		TestLog proxy = (TestLog)Proxy.newProxyInstance(testLog.getClass().getClassLoader()
				, testLog.getClass().getInterfaces(), testLogInterceptor);
		proxy.print();
	}
	
	public static void main(String[] args) {
		TestLog testLog = new TestLogImpl();
		TestLogInterceptor testLogInterceptor = new TestLogInterceptor();
		testLogInterceptor.setTarget(testLog);
		TestLog proxy = (TestLog)Proxy.newProxyInstance(testLog.getClass().getClassLoader()
				, testLog.getClass().getInterfaces(), testLogInterceptor);
		proxy.print();
		try {
			new TestProxy().printClass();
		} catch (Exception e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}
	
	public void printClass() throws Exception {
		ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
        Class cla = classLoader.getClass();
        while (cla != ClassLoader.class)
            cla = cla.getSuperclass();
        Field field = cla.getDeclaredField("classes");
        field.setAccessible(true);
        Vector v = (Vector) field.get(classLoader);
        for (int i = 0; i < v.size(); i++) {
            System.out.print(((Class)v.get(i)).getName()+",");
            if(i%10 == 0)System.out.println("");
        }
	}
}

java.lang.NoClassDefFoundError: org/junit/runner/manipulation/Filter