差異處
這裏顯示兩個版本的差異處。
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java:basic:classloader:duplicate_class_def_error [2016/12/15 13:51] tony |
java:basic:classloader:duplicate_class_def_error [2023/06/25 09:48] |
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| - | {{tag>java}} | ||
| - | ====== Classloader Error: attempted duplicate class definition for name ====== | ||
| - | ===== Problem ===== | ||
| - | 在寫plugin相關程式時，會去override classloader做成自己想要的載入形式。而這陣子，偶爾會發生如以下Error: | ||
| - | <code> | ||
| - | ava.lang.LinkageError: loader (instance of org/tonylin/FunnyClassLoader): attempted duplicate class definition for name: "org/apache/commons/cli/BasicParser" | ||
| - | </code> | ||
| - | 而我們的實做是去extend java.net.URLClassLoader，其中關鍵程式碼如下: | ||
| - | <code java> | ||
| - | private Class<?> loadClass(String className) { | ||
| - | Class<?> clazz = findLoadedClass(className); | ||
| - | if (clazz != null) { | ||
| - | return clazz; | ||
| - | } | ||
| - | |||
| - | // load locally | ||
| - | try { | ||
| - | clazz = findClass(className); | ||
| - | return clazz; | ||
| - | } catch (ClassNotFoundException e) { | ||
| - | // ignore | ||
| - | } | ||
| - | |||
| - | // use the standard URLClassLoader (which follows normal parent | ||
| - | // delegation) | ||
| - | try { | ||
| - | return super.loadClass(className); | ||
| - | } catch (ClassNotFoundException e) { | ||
| - | return null; | ||
| - | } | ||
| - | } | ||
| - | </code> | ||
| - | ===== Solutions ===== | ||
| - | 我寫了一個簡單的單元測試去trace這個問題，而內容為: | ||
| - | * 新增一個jar檔到FunnyClassLoader的classpath中。 | ||
| - | * 產生5個thread去load某個jar檔中的class。 | ||
| - | * 驗證正確完成的工作數量為5。 | ||
| - | <code java> | ||
| - | @Test | ||
| - | public void testConcurrentLoad() throws Exception{ | ||
| - | mClassLoader = new FunnyClassLoader(Thread.currentThread().getContextClassLoader()); | ||
| - | mClassLoader.addURL(new File("./testdata/commons-cli-1.2.jar")); | ||
| - | |||
| - | |||
| - | List<Thread> threads = new ArrayList<>(); | ||
| - | List<String> passThread = new ArrayList<>(); | ||
| - | int size = 5; | ||
| - | CountDownLatch latch = new CountDownLatch(size); | ||
| - | |||
| - | for( int i = 0 ; i < size ; i ++ ){ | ||
| - | |||
| - | Thread t = new Thread(()->{ | ||
| - | try { | ||
| - | mClassLoader.loadClass("org.apache.commons.cli.BasicParser"); | ||
| - | System.out.println("pass: " + Thread.currentThread().getName()); | ||
| - | passThread.add(Thread.currentThread().getName()); | ||
| - | } catch (Exception e) { | ||
| - | e.printStackTrace(); | ||
| - | } finally { | ||
| - | latch.countDown(); | ||
| - | } | ||
| - | }); | ||
| - | threads.add(t); | ||
| - | } | ||
| - | threads.parallelStream().forEach(t->t.start()); | ||
| - | |||
| - | latch.await(); | ||
| - | |||
| - | assertEquals(threads.size(), passThread.size()); | ||
| - | } | ||
| - | </code> | ||
| - | ===== ===== | ||
| - | ---- | ||
| - | \\ | ||
| - | ~~DISQUS~~ | ||
| - | |||
