Java reflection advanced

We usually use reflection The first way, first let’s take a look at Class.forName(clssName):
Note: The incoming className must be Full path of the class, otherwise an error java.lang.ClassNotFoundException will be reported.

public static Class<?> forName(String className)                
throws ClassNotFoundException {        
return forName0(className, true, ClassLoader.getCallerClassLoader());
    }

By calling the forName0 method, use ClassLoader.getCallerClassLoader() to load ClassLoader

    // Returns the invoker's class loader, or null if none.
    // NOTE: This must always be invoked when there is exactly one intervening
    // frame from the core libraries on the stack between this method's
    // invocation and the desired invoker.
    static ClassLoader getCallerClassLoader() {
        // NOTE use of more generic Reflection.getCallerClass()
        Class caller = Reflection.getCallerClass(3);
        // This can be null if the VM is requesting it        
        if (caller == null) {            
        return null;
        }
        // Circumvent security check since this is package-private        
        return caller.getClassLoader0();
    }

After getting the ClassLoader, call claser.getClassLoader0() this is a private package that avoids security checks.

 // Package-private to allow ClassLoader access
    native ClassLoader getClassLoader0();

1. What is ClassLoader?

We usually use reflection The first way, first let’s take a look at Class.forName(clssName):
Note : The passed in className must be the full path of the class, otherwise an error java.lang.ClassNotFoundException will be reported.

public static Class<?> forName(String className)                
throws ClassNotFoundException {        
return forName0(className, true, ClassLoader.getCallerClassLoader());
    }

By calling the forName0 method, use ClassLoader.getCallerClassLoader() to load ClassLoader

    // Returns the invoker's class loader, or null if none.
    // NOTE: This must always be invoked when there is exactly one intervening
    // frame from the core libraries on the stack between this method's
    // invocation and the desired invoker.
    static ClassLoader getCallerClassLoader() {
        // NOTE use of more generic Reflection.getCallerClass()
        Class caller = Reflection.getCallerClass(3);
        // This can be null if the VM is requesting it        
        if (caller == null) {            
        return null;
        }
        // Circumvent security check since this is package-private        
        return caller.getClassLoader0();
    }

After getting the ClassLoader, call claser.getClassLoader0() this is a private package that avoids security checks.

 // Package-private to allow ClassLoader access
    native ClassLoader getClassLoader0();

1. What is ClassLoader?

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