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Hi ! 我是小小,今天我们又见面了,今日的主要内容是MyBatis的size方法使用的主要的注意事项。
前言
MyBatis 是一个开源的轻量级的半自动化的 ORM 框架,用于面向对象和关系型数据库的映射,其中 xml 文件,和sql语句结合,最大的特点,应用程序sql解耦。OGNL表达式,是MyBatis中的广泛应用,是一种EL语言,用于设置和获取 Java 对象的属性,并且可以对列表进行投影和执行lambda表达式,ognl提供了简单,便于执行的ognl表达式。一个线上服务,经常会出现一个异常,构造各种OGNL表达式为空的情况都会重现该异常,具体的堆栈信息如下:
- ### Error querying database. Cause: org.apache.ibatis.builder.BuilderException: Error evaluating expression 'list != null and list.size() > 0'. Cause: org.apache.ibatis.ognl.MethodFailedException: Method "size" failed for object [1] [java.lang.IllegalAccessException: Class org.apache.ibatis.ognl.OgnlRuntime can not access a member of class java.util.Collections$SingletonList with modifiers "public"]
- ### Cause: org.apache.ibatis.builder.BuilderException: Error evaluating expression 'list != null and list.size() > 0'. Cause: org.apache.ibatis.ognl.MethodFailedException: Method "size" failed for object [1] [java.lang.IllegalAccessException: Class org.apache.ibatis.ognl.OgnlRuntime can not access a member of class java.util.Collections$SingletonList with modifiers "public"]
- at org.apache.ibatis.exceptions.ExceptionFactory.wrapException(ExceptionFactory.java:23) org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:107)
- at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:98)
- at cn.com.shaobingmm.MybatisBugTest$2.run(MybatisBugTest.java:88)
- at java.lang.Thread.run(Thread.java:745)
- Caused by: org.apache.ibatis.builder.BuilderException: Error evaluating expression 'list != null and list.size() > 0'. Cause: org.apache.ibatis.ognl.MethodFailedException: Method "size" failed for object [1] [java.lang.IllegalAccessException: Class org.apache.ibatis.ognl.OgnlRuntime can not access a member of class java.util.Collections$SingletonList with modifiers "public"]
- at org.apache.ibatis.scripting.xmltags.OgnlCache.getValue(OgnlCache.java
- at:47)
- at org.apache.ibatis.scripting.xmltags.ExpressionEvaluator.evaluateBoolean(ExpressionEvaluator.java:29)
- at org.apache.ibatis.scripting.xmltags.IfSqlNode.apply(IfSqlNode.java:30)
- at org.apache.ibatis.scripting.xmltags.MixedSqlNode.apply(MixedSqlNode.java:29)
- at org.apache.ibatis.scripting.xmltags.TrimSqlNode.apply(TrimSqlNode.java:51)
- at org.apache.ibatis.scripting.xmltags.MixedSqlNode.apply(MixedSqlNode.java:29)
- at org.apache.ibatis.scripting.xmltags.DynamicSqlSource.getBoundSql(DynamicSqlSource.java:37)
- at org.apache.ibatis.mapping.MappedStatement.getBoundSql(MappedStatement.java:275)
- at org.apache.ibatis.executor.CachingExecutor.query(CachingExecutor.java:79)
- at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:104)
- ... 3 more
- Caused by: org.apache.ibatis.ognl.MethodFailedException: Method "size" failed for object [1] [java.lang.IllegalAccessException: Class org.apache.ibatis.ognl.OgnlRuntime can not access a member of class java.util.Collections$SingletonList with modifiers "public"]
- at org.apache.ibatis.ognl.OgnlRuntime.callAppropriateMethod(OgnlRuntime.java:837)
- at org.apache.ibatis.ognl.ObjectMethodAccessor.callMethod(ObjectMethodAccessor.java:61)
- at org.apache.ibatis.ognl.OgnlRuntime.callMethod(OgnlRuntime.java:860)
- at org.apache.ibatis.ognl.ASTMethod.getValueBody(ASTMethod.java:73)
- at org.apache.ibatis.ognl.SimpleNode.evaluateGetValueBody(SimpleNode.java:170)
- at org.apache.ibatis.ognl.SimpleNode.getValue(SimpleNode.java:210)
- at org.apache.ibatis.ognl.ASTChain.getValueBody(ASTChain.java:109)
- at org.apache.ibatis.ognl.SimpleNode.evaluateGetValueBody(SimpleNode.java:170)
- at org.apache.ibatis.ognl.SimpleNode.getValue(SimpleNode.java:210)
- at org.apache.ibatis.ognl.ASTGreater.getValueBody(ASTGreater.java:49)
- at org.apache.ibatis.ognl.SimpleNode.evaluateGetValueBody(SimpleNode.java:170)
- at org.apache.ibatis.ognl.SimpleNode.getValue(SimpleNode.java:210)
- at org.apache.ibatis.ognl.ASTAnd.getValueBody(ASTAnd.java:56)
- at org.apache.ibatis.ognl.SimpleNode.evaluateGetValueBody(SimpleNode.java:170)
- at org.apache.ibatis.ognl.SimpleNode.getValue(SimpleNode.java:210)
- at org.apache.ibatis.ognl.Ognl.getValue(Ognl.java:333)
- at org.apache.ibatis.ognl.Ognl.getValue(Ognl.java:413)
- at org.apache.ibatis.ognl.Ognl.getValue(Ognl.java:395)
- at org.apache.ibatis.scripting.xmltags.OgnlCache.getValue(OgnlCache.java:45)
- ... 12 more
List的size方法明明有public,还不可访问,该异常在测试环境未重现,但是在接口的完整调用链路中出错的次数占总的调用次数的0.01%,这是概率性事件。
模拟测试
编写模拟多线程并发读取公司列表的测试代码
"CompanyMapper"> - <select id="getCompanysByIds"resultType="cn.com.shaobingmm.Company">
- select *
- from company
- <where>
-
"list != null and list.size() > 0" > - and id in
-
"list" item="id" open="(" separator="," close=")">#{id} -
-
- where>
- select>
-
多线程下进行压力测试
- String resource = "mybatis-config.xml";
- InputStream in = null;
- try {
- in = Resources.getResourceAsStream(resource);
- SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(in);
- final List
ids = Collections.singletonList(1L); - final SqlSession session = sqlSessionFactory.openSession();
- final CountDownLatch mCountDownLatch = new CountDownLatch(1);
- for (int i = 0; i < 50; i++) {
- Thread thread = new Thread(new Runnable() {
- public void run() {
- try {
- mCountDownLatch.await();
- } catch (InterruptedException e) {
- e.printStackTrace();
- }
- for (int k = 0; k < 100; k++) {
- session.selectList("CompanyMapper.getCompanysByIds", ids);
- }
- }
- });
- thread.start();
- }
- mCountDownLatch.countDown();
- synchronized (MybatisBugTest.class) {
- try {
- MybatisBugTest.class.wait();
- } catch (InterruptedException e) {
- e.printStackTrace();
- }
- }
-
- } catch (IOException e) {
- e.printStackTrace();
- } catch (Throwable e) {
- e.printStackTrace();
- } finally {
- if (in != null)
- try {
- in.close();
- } catch (IOException e) {
- e.printStackTrace();
- }
- }
上述代码在并发的时候会出现异常。
- Caused by: org.apache.ibatis.ognl.MethodFailedException: Method "size" failed for object [1] [java.lang.IllegalAccessException: Class org.apache.ibatis.ognl.OgnlRuntime can not access a member of class java.util.Collections$SingletonList with modifiers "public"]
- at org.apache.ibatis.ognl.OgnlRuntime.callAppropriateMethod(OgnlRuntime.java:837)
异常信息表明ognlRuntime类不能访问
查看源码,破案
java.util.Collections的私有成员SingletonList。查看源代码,可以知道锁定在invokeMethod方法上。
- public static Object callAppropriateMethod(OgnlContext context, Object source, Object target, String methodName, String propertyName, List methods, Object[] args) throws MethodFailedException {
- Object reason = null;
- Object[] actualArgs = objectArrayPool.create(args.length);
-
- try {
- Method e = getAppropriateMethod(context, source, target, methodName, propertyName, methods, args, actualArgs);
- if(e == null || !isMethodAccessible(context, source, e, propertyName)) {
- StringBuffer buffer = new StringBuffer();
- if(args != null) {
- int i = 0;
-
- for(int ilast = args.length - 1; i <= ilast; ++i) {
- Object arg = args[i];
- buffer.append(arg == null?NULL_STRING:arg.getClass().getName());
- if(i < ilast) {
- buffer.append(", ");
- }
- }
- }
-
- throw new NoSuchMethodException(methodName + "(" + buffer + ")");
- }
-
- Object var14 = invokeMethod(target, e, actualArgs);
- return var14;
- } catch (NoSuchMethodException var21) {
- reason = var21;
- } catch (IllegalAccessException var22) {
- reason = var22;
- } catch (InvocationTargetException var23) {
- reason = var23.getTargetException();
- } finally {
- objectArrayPool.recycle(actualArgs);
- }
-
- throw new MethodFailedException(source, methodName, (Throwable)reason);
- }
其方法代码
- public static Object invokeMethod(Object target, Method method, Object[] argsArray) throws InvocationTargetException, IllegalAccessException {
- boolean wasAccessible = true;
- if(securityManager != null) {
- try {
- securityManager.checkPermission(getPermission(method));
- } catch (SecurityException var6) {
- throw new IllegalAccessException("Method [" + method + "] cannot be accessed.");
- }
- }
-
- if((!Modifier.isPublic(method.getModifiers()) || !Modifier.isPublic(method.getDeclaringClass().getModifiers())) && !(wasAccessible = method.isAccessible())) {
- method.setAccessible(true); (1)
- }
-
- Object result = method.invoke(target, argsArray); (3)
- if(!wasAccessible) {
- method.setAccessible(false); (2)
- }
-
- return result;
- }
问题出现在meta是一个共享变量,即
- public int java.util.Collections$SingletonList.size()
当,第一个线程t1到第一行代码允许method方法可以调用,第二个线程t2,执行到2把方法method设置为不可访问,接着t1又执行,此时行列3会发生异常。
升级版本
lgnl2.7,已经修复了这个问题,所以修复后的代码如下
- public static Object invokeMethod(Object target, Method method, Object[] argsArray) throws InvocationTargetException, IllegalAccessException {
- boolean syncInvoke = false;
- boolean checkPermission = false;
- int mHash = method.hashCode();
- synchronized(method) {
- if(_methodAccessCache.get(Integer.valueOf(mHash)) == null || _methodAccessCache.get(Integer.valueOf(mHash)) == Boolean.TRUE) {
- syncInvoke = true;
- }
-
- if(_securityManager != null && _methodPermCache.get(Integer.valueOf(mHash)) == null || _methodPermCache.get(Integer.valueOf(mHash)) == Boolean.FALSE) {
- checkPermission = true;
- }
- }
-
- boolean wasAccessible = true;
- Object result;
- if(syncInvoke) {
- synchronized(method) {
- if(checkPermission) {
- try {
- _securityManager.checkPermission(getPermission(method));
- _methodPermCache.put(Integer.valueOf(mHash), Boolean.TRUE);
- } catch (SecurityException var12) {
- _methodPermCache.put(Integer.valueOf(mHash), Boolean.FALSE);
- throw new IllegalAccessException("Method [" + method + "] cannot be accessed.");
- }
- }
-
- if(Modifier.isPublic(method.getModifiers()) && Modifier.isPublic(method.getDeclaringClass().getModifiers())) {
- _methodAccessCache.put(Integer.valueOf(mHash), Boolean.FALSE);
- } else if(!(wasAccessible = method.isAccessible())) {
- method.setAccessible(true);
- _methodAccessCache.put(Integer.valueOf(mHash), Boolean.TRUE);
- } else {
- _methodAccessCache.put(Integer.valueOf(mHash), Boolean.FALSE);
- }
-
- result = method.invoke(target, argsArray);
- if(!wasAccessible) {
- method.setAccessible(false);
- }
- }
- } else {
- if(checkPermission) {
- try {
- _securityManager.checkPermission(getPermission(method));
- _methodPermCache.put(Integer.valueOf(mHash), Boolean.TRUE);
- } catch (SecurityException var11) {
- _methodPermCache.put(Integer.valueOf(mHash), Boolean.FALSE);
- throw new IllegalAccessException("Method [" + method + "] cannot be accessed.");
- }
- }
-
- result = method.invoke(target, argsArray);
- }
-
- return result;
- }
关于作者
我是小小,一个生于二线,活在一线城市的程序猿,我是小小,我们下期再见。