【0】README

版权声明：本文为博主原创文章，未经博主允许不得转载。 https://blog.csdn.net/PacosonSWJTU/article/details/51076989

【0】README

0.1）本文主要对类加载器进行分析，且 URLClassLoader是 ClassLoader的子类；

0.2）关于如何设置类加载器的加载路径，参见 对servlet容器的补充

【1】URLClassLoader类加载器

1.1）URLClassLoader的一种加载方式

1. package com.tomcat.classloader;

2.  

3. import java.io.File;

4. import java.lang.reflect.Constructor;

5. import java.lang.reflect.Method;

6. import java.net.URL;

7. import java.net.URLClassLoader;

8.  

9. public class URLClassLoaderTest {

10.  

11. public final static String dir = System.getProperty("user.dir") + File.separator + "src" + File.separator;

12. public static void main(String[] args) throws Exception {

13.  

14. // Getting the jar URL which contains target class

15. URL[] classLoaderUrls = new URL[]{new URL("file:" + dir)};

16.  

17. // Create a new URLClassLoader

18. URLClassLoader urlClassLoader = new URLClassLoader(classLoaderUrls);

19.  

20. // Load the target class

21. Class<?> beanClass = urlClassLoader.loadClass("com.tomcat.test.Bean");

22.  

23. // Create a new instance from the loaded class

24. Constructor<?> constructor = beanClass.getConstructor();

25. Object beanObj = constructor.newInstance();

26.  

27. // Getting a method from the loaded class and invoke it

28. Method method = beanClass.getMethod("sayHello");

29. method.invoke(beanObj);

30. }

31. }

1. package com.tomcat.test;

2.  

3. public class Bean {

4.  

5. public void sayHello() {

6. System.out.println("Hello from loaded Bean class for test!!!");

7. }

8. }

1.2）URLClassLoader的另一种加载方式

1. package com.tomcat.classloader;

2.  

3. import java.io.File;

4. import java.lang.reflect.Constructor;

5. import java.lang.reflect.Method;

6. import java.net.MalformedURLException;

7. import java.net.URL;

8. import java.net.URLClassLoader;

9.  

10. public class URLClassLoaderTest {

11. public final static String dir = System.getProperty("user.dir") +

12. File.separator + "webroot" + File.separator;

13. public static void main(String[] args) {

14. try {

15. File file = new File(dir);

16. URL url = file.toURI().toURL(); // attend this line

17. URL[] urls = new URL[]{url};

18. URLClassLoader loader = new URLClassLoader(urls, null, null);

19. System.out.println("test = " + loader.getURLs()[0].toString());

20.  

21. Class<?> beanClass = loader.loadClass("servlet.Bean");

22. Object obj = beanClass.newInstance();

23. Method method = beanClass.getMethod("sayHello");

24. method.invoke(obj);

25. } catch (Exception e) {

26. e.printStackTrace();

27. }

28. }

29. }

【2】ClassLoader类加载器的加载方式

1. package com.tomcat.test;

2.  

3. import java.lang.reflect.Constructor;

4. import java.lang.reflect.Method;

5.  

6. public class ClassLoaderTest {

7. // 第一种加载类的方式

8. public static void main1(String[] args) throws Exception {

9. Class<?> newClass = Class.forName("com.tomcat.classloader.Bean");

10. Constructor constructor = newClass.getConstructor();

11. Object obj = constructor.newInstance();

12. Method method = newClass.getMethod("sayHello");

13. method.invoke(obj);

14. }

15.  

16. // 第二种加载类的方式

17. public static void main(String[] args) throws Exception {

18. ClassLoader loader = Thread.currentThread().getContextClassLoader();

19. Class<?> newClass = loader.loadClass("com.tomcat.classloader.Bean");

20. Constructor constructor = newClass.getConstructor();

21. Object obj = constructor.newInstance();

22. Method method = newClass.getMethod("sayHello");

23. method.invoke(obj);

24. }

25. }