警惕，Mybatis的Size()方法竟然有坑！
作者： 小明菜市場(chǎng)
MyBatis 是一個(gè)開(kāi)源的輕量級(jí)的半自動(dòng)化的 ORM 框架，用于面向?qū)ο蠛完P(guān)系型數(shù)據(jù)庫(kù)的映射，其中 xml 文件，和sql語(yǔ)句結(jié)合，最大的特點(diǎn)，應(yīng)用程序sql解耦。
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Hi ! 我是小小，今天我們又見(jiàn)面了，今日的主要內(nèi)容是MyBatis的size方法使用的主要的注意事項(xiàng)。
前言
MyBatis 是一個(gè)開(kāi)源的輕量級(jí)的半自動(dòng)化的 ORM 框架，用于面向?qū)ο蠛完P(guān)系型數(shù)據(jù)庫(kù)的映射，其中 xml 文件，和sql語(yǔ)句結(jié)合，最大的特點(diǎn)，應(yīng)用程序sql解耦。OGNL表達(dá)式，是MyBatis中的廣泛應(yīng)用，是一種EL語(yǔ)言，用于設(shè)置和獲取 Java 對(duì)象的屬性，并且可以對(duì)列表進(jìn)行投影和執(zhí)行l(wèi)ambda表達(dá)式，ognl提供了簡(jiǎn)單，便于執(zhí)行的ognl表達(dá)式。一個(gè)線上服務(wù)，經(jīng)常會(huì)出現(xiàn)一個(gè)異常，構(gòu)造各種OGNL表達(dá)式為空的情況都會(huì)重現(xiàn)該異常，具體的堆棧信息如下：
- ### 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，還不可訪問(wèn)，該異常在測(cè)試環(huán)境未重現(xiàn)，但是在接口的完整調(diào)用鏈路中出錯(cuò)的次數(shù)占總的調(diào)用次數(shù)的0.01%，這是概率性事件。
模擬測(cè)試
編寫(xiě)模擬多線程并發(fā)讀取公司列表的測(cè)試代碼
- <mapper namespace="CompanyMapper">
- <select id="getCompanysByIds"resultType="cn.com.shaobingmm.Company">
- select *
- from company
- <where>
- <if test="list != null and list.size() > 0">
- and id in
- <foreach collection="list" item="id" open="(" separator="," close=")">#{id}
- </foreach>
- </if>
- </where>
- </select>
- </mapper>
多線程下進(jìn)行壓力測(cè)試
- String resource = "mybatis-config.xml";
- InputStream in = null;
- try {
- in = Resources.getResourceAsStream(resource);
- SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(in);
- final List<Long> 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();
- }
- }
上述代碼在并發(fā)的時(shí)候會(huì)出現(xiàn)異常。
- 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)
異常信息表明ognlRuntime類(lèi)不能訪問(wèn)
查看源碼，破案
java.util.Collections的私有成員SingletonList。查看源代碼，可以知道鎖定在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);
- }
其方法代碼
- 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;
- }
問(wèn)題出現(xiàn)在meta是一個(gè)共享變量，即
- public int java.util.Collections$SingletonList.size()
當(dāng)，第一個(gè)線程t1到第一行代碼允許method方法可以調(diào)用，第二個(gè)線程t2，執(zhí)行到2把方法method設(shè)置為不可訪問(wèn)，接著t1又執(zhí)行，此時(shí)行列3會(huì)發(fā)生異常。
升級(jí)版本
lgnl2.7，已經(jīng)修復(fù)了這個(gè)問(wèn)題，所以修復(fù)后的代碼如下
- 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;
- }
關(guān)于作者
我是小小，一個(gè)生于二線，活在一線城市的程序猿，我是小小，我們下期再見(jiàn)。
責(zé)任編輯：武曉燕
來(lái)源：
小明菜市場(chǎng)
