使用类来得到工程目录下的文件绝对路经
public class TestClassLoader {

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

new TestClassLoader().b();
}

private void b() {
URL url1 = TestClassLoader.class.getClassLoader().getResource("a.txt");
URL url2 = TestClassLoader.this.getClass().getResource("/a.txt");
URL url3 = Thread.currentThread().getContextClassLoader().getResource("a.txt");
URL url4 = TestClassLoader.class.getClassLoader().getSystemResource("a.txt");

System.out.println(url1);
System.out.println(url2);
System.out.println(url3);
System.out.println(url4);
}

}