Java-类加载器

package com.yutao.day1;

public class ClassLoaderLearn {
    public static void main(String[] args) {
        System.out.println("hello");
    }
}

// 反射加载
Class.forName("com.xxx.xx.xx..x.x.x.xx");//默认会初始化被加载类的静态属性和方法

// ClassLoader加载
this.getClass().getClassLoader().loadClass("com.xxx.xx.xx..x.x.x.xx");//默认不会初始化

protected Class<?> loadClass(String name, Boolean resolve) throws ClassNotFoundException
    {
	synchronized (getClassLoadingLock(name)) {
		// First, check if the class has already been loaded
		Class<?> c = findLoadedClass(name);
		if (c == null) {
			long t0 = System.nanoTime();
			try {
				if (parent != null) {
					c = parent.loadClass(name, false);
				} else {
					c = findBootstrapClassOrNull(name);
				}
			}
			catch (ClassNotFoundException e) {
				// ClassNotFoundException thrown if class not found
				// from the non-null parent class loader
			}
			if (c == null) {
				// If still not found, then invoke findClass in order
				// to find the class.
				long t1 = System.nanoTime();
				c = findClass(name);
				// this is the defining class loader; record the stats
				sun.misc.PerfCounter.getParentDelegationTime().addTime(t1 - t0);
				sun.misc.PerfCounter.getFindClassTime().addElapsedTimeFrom(t1);
				sun.misc.PerfCounter.getFindClasses().increment();
			}
		}
		if (resolve) {
			resolveClass(c);
		}
		return c;
	}
}

    /**
     * Finds the class with the specified <a href="#name">binary name</a>.
     * This method should be overridden by class loader implementations that
     * follow the delegation model for loading classes, and will be invoked by
     * the {@link #loadClass <tt>loadClass</tt>} method after checking the
     * parent class loader for the requested class.  The default implementation
     * throws a <tt>ClassNotFoundException</tt>.
     *
     * @param  name
     *         The <a href="#name">binary name</a> of the class
     *
     * @return  The resulting <tt>Class</tt> object
     *
     * @throws  ClassNotFoundException
     *          If the class could not be found
     *
     * @since  1.2
     */
    protected Class<?> findClass(String name) throws ClassNotFoundException {
        throw new ClassNotFoundException(name);
    }

    /**
     * Returns the class with the given <a href="#name">binary name</a> if this
     * loader has been recorded by the Java virtual machine as an initiating
     * loader of a class with that <a href="#name">binary name</a>.  Otherwise
     * <tt>null</tt> is returned.
     *
     * @param  name
     *         The <a href="#name">binary name</a> of the class
     *
     * @return  The <tt>Class</tt> object, or <tt>null</tt> if the class has
     *          not been loaded
     *
     * @since  1.1
     */
    protected final Class<?> findLoadedClass(String name) {
        if (!checkName(name))
            return null;
        return findLoadedClass0(name);
    }

    /**
     * Converts an array of bytes into an instance of class <tt>Class</tt>.
     * Before the <tt>Class</tt> can be used it must be resolved.  This method
     * is deprecated in favor of the version that takes a <a
     * href="#name">binary name</a> as its first argument, and is more secure.
     *
     * @param  b
     *         The bytes that make up the class data.  The bytes in positions
     *         <tt>off</tt> through <tt>off+len-1</tt> should have the format
     *         of a valid class file as defined by
     *         <cite>The Java&trade; Virtual Machine Specification</cite>.
     *
     * @param  off
     *         The start offset in <tt>b</tt> of the class data
     *
     * @param  len
     *         The length of the class data
     *
     * @return  The <tt>Class</tt> object that was created from the specified
     *          class data
     *
     * @throws  ClassFormatError
     *          If the data did not contain a valid class
     *
     * @throws  IndexOutOfBoundsException
     *          If either <tt>off</tt> or <tt>len</tt> is negative, or if
     *          <tt>off+len</tt> is greater than <tt>b.length</tt>.
     *
     * @throws  SecurityException
     *          If an attempt is made to add this class to a package that
     *          contains classes that were signed by a different set of
     *          certificates than this class, or if an attempt is made
     *          to define a class in a package with a fully-qualified name
     *          that starts with "{@code java.}".
     *
     * @see  #loadClass(String, boolean)
     * @see  #resolveClass(Class)
     *
     * @deprecated  Replaced by {@link #defineClass(String, byte[], int, int)
     * defineClass(String, byte[], int, int)}
     */
    @Deprecated
    protected final Class<?> defineClass(byte[] b, int off, int len)
        throws ClassFormatError
    {
        return defineClass(null, b, off, len, null);
    }

    /**
     * Links the specified class.  This (misleadingly named) method may be
     * used by a class loader to link a class.  If the class <tt>c</tt> has
     * already been linked, then this method simply returns. Otherwise, the
     * class is linked as described in the "Execution" chapter of
     * <cite>The Java&trade; Language Specification</cite>.
     *
     * @param  c
     *         The class to link
     *
     * @throws  NullPointerException
     *          If <tt>c</tt> is <tt>null</tt>.
     *
     * @see  #defineClass(String, byte[], int, int)
     */
    protected final void resolveClass(Class<?> c) {
        resolveClass0(c);
    }

package com.yutao.day1;

public class execcalc {
    public execcalc() {
        System.out.println("Test success!!!");
        try {
            Runtime.getRuntime().exec("cmd /c calc.exe");
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}
//E:\github\JavaSecLearn\Code\JavaSecLearn\src\com\yutao\day1

package com.yutao.day1;

import java.io.File;
import java.net.MalformedURLException;
import java.net.URI;
import java.net.URL;
import java.net.URLClassLoader;

public class ClassLoaderLearn {
    public static void main(String[] args) throws ClassNotFoundException, NullPointerException, InstantiationException, IllegalAccessException, MalformedURLException {
        File file = new File("E:\\github\\JavaSecLearn\\Code\\JavaSecLearn\\src\\com\\yutao\\day1\\");
        URI uri = file.toURI();
        URL url = uri.toURL();

        URLClassLoader classLoader = new URLClassLoader(new URL[]{url});
        Class clazz = classLoader.loadClass("com.yutao.day1.execcalc");
        clazz.newInstance();
    }
}