ClassLoader在Tomcat里面内存泄露问题
项目里面有一个验证配置的功能。主要流程如下：
一开始代码写成这样，只是在web项目里面直接调用check逻辑
但是这样会有一个问题，就是即使public CheckResult test() { URLClassLoader classLoader = null; File dataFile = new File("xx.jar"); File checkFile = new File("resourceDir"); try { // 这里防止内存泄露,因为classLoader释放了,但里面的jar已经有缓存,没有释放 URL jarUrl = dataFile.toURI().toURL(); URLConnection jarConnection = jarUrl.openConnection(); jarConnection.setUseCaches(true); classLoader = new URLClassLoader(new URL[]{jarUrl}); Class centerClass = classLoader.loadClass("com.xx.data.DataCenter"); Object centerObject = centerClass.getMethod("getInstance").invoke(null); Field field = centerClass.getField("gameConfigGroup"); Object gameConfigGroupObject = field.get(centerObject); String uploadUrlPath = checkFile.toURI().toURL().toString(); Method loadMethod = gameConfigGroupObject.getClass().getDeclaredMethod("load", String.class); Method checkMethod = gameConfigGroupObject.getClass().getDeclaredMethod("check", gameConfigGroupObject.getClass()); loadMethod.invoke(gameConfigGroupObject, uploadUrlPath); checkMethod.invoke(gameConfigGroupObject, gameConfigGroupObject); return CheckResult.suc(); } catch (Exception e) { StringWriter writer = new StringWriter(); Throwable cause; Throwable resultCause = e; if (resultCause.getCause() == null) { resultCause.printStackTrace(new PrintWriter(writer)); } else { while (null != (cause = resultCause.getCause()) && (resultCause != cause)) { resultCause = cause; if (!(resultCause instanceof InvocationTargetException)) { resultCause.printStackTrace(new PrintWriter(writer)); } } } return CheckResult.err(writer.toString()); } finally { if (classLoader != null) { try { classLoader.close(); } catch (IOException e) { logger.error(e.getMessage(), e); } } } }
ClassLoader关闭了，但因为加载了一些static用作缓存，像logback日志类库等，会导致内存慢慢泄露。
然后这个问题一直在纠结，而ClassLoader的机制我又不是很熟，有一天突然灵光一闪，想到了用子进程。然后代码改成了这样：
这个思路很简单，就是起一个子进程，然后让这个子进程去执行public CheckResult test() { URLClassLoader classLoader = null; File dataFile = new File("xx.jar"); File checkFile = new File("resourceDir"); // 更新资源和代码, 并执行检测逻辑 StringWriter stringWriter = new StringWriter(); PrintWriter outputStream = new PrintWriter(stringWriter); try { String cmd = "java -XX:-OmitStackTraceInFastThrow -Xms512m -cp .:/usr/local/tomcat/apps CheckMain " + dataFile.getPath() + " " + checkFile.getCanonicalPath(); Process p = Runtime.getRuntime().exec(new String[]{"/bin/sh", "-c", "cd " + dataFile.getParent() + ";svn up;" + cmd}); StreamGobbler errorGobbler = new StreamGobbler(p.getErrorStream(), "ERROR", outputStream); StreamGobbler outputGobbler = new StreamGobbler(p.getInputStream(), ""); taskExecutor.execute(errorGobbler); taskExecutor.execute(outputGobbler); long start = System.currentTimeMillis(); logger.info("start waiting...[{}]", cmd); try { p.waitFor(20, TimeUnit.SECONDS); } finally { p.destroy(); } outputStream.flush(); String rs = stringWriter.toString(); logger.info("finish, useTime:[{}]", (System.currentTimeMillis() - start)); if (StringUtils.isNotBlank(rs)) { return CheckResult.err(rs); } } catch (Exception e) { logger.error(e.getMessage(), e); StringWriter writer = new StringWriter(); e.printStackTrace(new PrintWriter(writer)); return CheckResult.err(writer.toString()); } finally { outputStream.close(); } return CheckResult.suc(); }
check逻辑，上面那个CheckMain代码如下：
import java.io.File; import java.io.IOException; import java.lang.reflect.Field; import java.lang.reflect.Method; import java.net.URL; import java.net.URLClassLoader; import java.nio.file.Files; import java.nio.file.Paths; /** * 因为在tomcat里面直接执行这个检测逻辑, 会导致有一些静态变量的内存泄露, 所以暂时采用的解决方法时用Runtime启动一个子进程来执行这个逻辑 * Created by wait on 2016/6/15. */ public class CheckMain { static class ExtClassLoader extends URLClassLoader { private String path; public ExtClassLoader(URL[] urls, String path) { super(urls); this.path = path; } public Class loadClass(String name) throws ClassNotFoundException { // 这里用来替换地图, 暂时不要那个寻路算法 if (name.equals("com.xx.data.game.config.impl.Q_mapConfig")) { try { byte[] buf = Files.readAllBytes(Paths.get(path, "Q_mapConfig.class")); return defineClass(name, buf, 0, buf.length); } catch (IOException e) { throw new ClassNotFoundException(name, e); } } return super.loadClass(name); } } private static void check(String dataPath, String urlPath) { File dataFile = new File(dataPath); URLClassLoader classLoader = null; try { String uploadUrlPath = new File(urlPath).toURI().toURL().toString(); URL[] loadUrl = new URL[]{dataFile.toURI().toURL(), dataFile.getParentFile().toURI().toURL()}; classLoader = new ExtClassLoader(loadUrl, "/usr/local/tomcat/apps"); Class<?> centerClass = classLoader.loadClass("com.xx.data.DataCenter"); Object centerObject = centerClass.getMethod("getInstance").invoke(null); Field field = centerClass.getField("gameConfigGroup"); Object gameConfigGroupObject = field.get(centerObject); Method loadMethod = gameConfigGroupObject.getClass().getDeclaredMethod("load", String.class); Method checkMethod = gameConfigGroupObject.getClass().getDeclaredMethod("check", gameConfigGroupObject.getClass()); loadMethod.invoke(gameConfigGroupObject, uploadUrlPath); checkMethod.invoke(gameConfigGroupObject, gameConfigGroupObject); } catch (Exception e) { Throwable cause; Throwable resultCause = e; if (resultCause.getCause() == null) { e.printStackTrace(); } else { while (null != (cause = resultCause.getCause()) && (resultCause != cause)) { resultCause = cause; resultCause.printStackTrace(); } } } finally { if (classLoader != null) { try { classLoader.close(); } catch (IOException e) { e.printStackTrace(); } } } } public static void main(String[] args) { if (args.length < 2) { return; } // args = new String[]{"E:\\game\\data.jar", "E:\\3_res"}; long start = System.currentTimeMillis(); System.out.println("args:" + args[0] + ", " + args[1]); check(args[0], args[1]); System.out.println("finish:" + args[0] + ", " + args[1] + " useTime[ms]:" + (System.currentTimeMillis() - start)); } }
/usr/local/tomcat/apps目录下放置CheckMain.java和CheckMain.class，然后就搞掂了。
由于地图寻路算法需要做的预处理比较多，导致初始化比较慢，而其实验证配置并不需要寻路，所以我就把项目的Q_mapConfig初始化寻路那部分代码注释掉了。
这个检测接口的目的很简单，如果重启配置验证不过，会导致起不了服而导致测试的工作中断，所以才在重启前还有配置被修改时让他们先验证一下。但这个简简单单的接口，真是折腾了挺久的。只能说对ClassLoader的机制太不熟，我想了一下，应该像tomcat那种，独立加载webapp的可以实现资源分离的方法才是正解，但那个还需要去看看书，以后看到了再折腾了。
