如何使用ClassLoader加载类

Question

I have an interface named Operator the directory of this interface is d:\\operators Interface definition is like so :

package operators;

public interface Operator
{
    double calculate(double firstNumber,double secondNumber);
    String getSign();
}

In the main program (d:\\ProjectFile94.6.7\\main) I want load this interface and use it .I load interface like so :

String rootPath = System.getProperty("user.dir")+System.getProperty("file.separator");
            String operatorsPath = rootPath.replace("ProjectFile94.6.7" , "").replace("main" , "") + "operators";
System.out.println(operatorsPath);

//Load operators from another file
File operatorFile = new File(operatorsPath);
URL operatorFilePath = operatorFile.toURL();          
URL[] operatorFilePaths = new URL[]{operatorFilePath};
ClassLoader operatorsLoader = new URLClassLoader(operatorFilePaths);
Class operatorInterface = operatorsLoader.loadClass("operators.Operator");

The app compiled fine but at runtime I got this exception :

java.lang.ClassNotFoundException : operators.Operator

Answer 1

You must not append the package name in the classpath directory:

String operatorsPath = rootPath.replace("ProjectFile94.6.7" , "").replace("main" , "");

ie the directory path should be just D:/ . Otherwise, you're just telling the classloader to search for D:/operators/operators/Operator.class .