Flink plugin机制，结合SPI和自定义ClassLoader实现，允许冲突jar包并存，不用再修改代码等方式来统一class版本。

    下面代码模拟plugin的实现流程

    1. public interface IShout {
    2.     void shout();
    3.     boolean valid(String config);
    4. }
    6. public class Cat implements IShout {
    7.     @Override
    8.     public void shout() {
    9.         System.out.println(this.getClass().getProtectionDomain().getCodeSource().getLocation().getFile());
    10.         System.out.println("miao miao");
    11.     }
    13.     @Override
    14.     public boolean valid(String config) {
    15.         return config.equalsIgnoreCase("cat");
    16.     }
    17. }
    19. public class Dog implements IShout {
    20.     @Override
    21.     public void shout() {
    22.         System.out.println(this.getClass().getProtectionDomain().getCodeSource().getLocation().getFile());
    23.         System.out.println("wang wang");
    24.     }
    25.     @Override
    26.     public boolean valid(String config) {
    27.         return config.equalsIgnoreCase("dog");
    28.     }
    29. }
    31. public class MyClassLoader extends URLClassLoader {
    33.     public MyClassLoader(URL[] urls) {
    34.         super(urls);
    35.     }
    36.     @Override
    37.     protected Class<?> loadClass(final String name, final boolean resolve) throws ClassNotFoundException {
    38.         synchronized (getClassLoadingLock(name)) {
    39.             Class<?> c = findLoadedClass(name);
    40.             if (c == null) {
    41.                 try {
    42.                     //优先从当前路径下加载class
    43.                     c = findClass(name);
    44.                 } catch (ClassNotFoundException e) {
    45.                     c=getParent().loadClass(name);
    46.                 }
    47.             }
    49.             if (resolve) {
    50.                 resolveClass(c);
    51.             }
    53.             return c;
    54.         }
    55.     }
    56. }
    58. public class SPIMain {
    59.     public static void main(String[] args) throws IOException {
    60.         Path path = Files.createTempDirectory(Paths.get("c:/workspace/tmp"),"spi");
    61. //        path.toFile().deleteOnExit();
    62.         String catPath = Cat.class.getCanonicalName().replace(".", "/") + ".class";
    63.         File file = path.resolve(catPath).toFile();
    64.         file.getParentFile().mkdirs();
    66.         Files.copy(SPIMain.class.getClassLoader().getResourceAsStream(catPath), file.toPath());
    68.         ClassLoader subModuleClassLoader = new MyClassLoader(new URL[]{path.toUri().toURL()});
    69.         ServiceLoader<IShout> shouts = ServiceLoader.load(IShout.class,subModuleClassLoader);
    70.         String config="cat";
    71.         IShout shout = null;
    72.         for (IShout s : shouts) {
    73.             s.shout();
    74.             if(s.valid(config)){
    75.                 shout = s;
    76.                 break;
    77.             }
    78.         }
    79.         shout.shout();
    80.         IShout cat = new Cat();
    81.         cat.shout();
    82.     }
    83. }

    程序输出：

    1. /C:/workspace/github/JavaTest/java-test/target/classes/
    2. wang wang
    3. /c:/workspace/tmp/spi4806402692415880585/
    4. miao miao
    5. /c:/workspace/tmp/spi4806402692415880585/
    6. miao miao
    7. /C:/workspace/github/JavaTest/java-test/target/classes/
    8. miao miao