Analysis of MyBatis OGNL Concurrency Bug and Workarounds

To save time, here is the conclusion: there is indeed a problem (see the issue link: https://github.com/mybatis/mybatis-3/pull/384). Below is the source‑code analysis and handling process for those interested.

Bug fixes are mandatory; without fixing them, daily work can be severely disrupted.

Log

After deploying to the server, MyBatis threw an exception on a frequently used interface, threatening performance metrics.

2023-08-08 09:52:05,386|aaaaaaaaa|XXXXXXXXXXXXXX|unknown exception occurred
org.mybatis.spring.MyBatisSystemException: nested exception is org.apache.ibatis.builder.BuilderException: Error evaluating expression 'projects != null and projects.size() > 0 '. Cause: org.apache.ibatis.ognl.MethodFailedException: Method "size" failed for object [aaa,bbb,ccc] [java.lang.IllegalAccessException: Class org.apache.ibatis.ognl.OgnlRuntime can not access a member of class java.util.Arrays$ArrayList with modifiers "public"]
    at org.mybatis.spring.MyBatisExceptionTranslator.translateExceptionIfPossible(MyBatisExceptionTranslator.java:75) ~[mybatis-spring-1.2.2.jar:1.2.2]
    ... (stack trace truncated for brevity) ...
Caused by: org.apache.ibatis.builder.BuilderException: Error evaluating expression 'projects != null and projects.size() > 0 '. Cause: org.apache.ibatis.ognl.MethodFailedException: Method "size" failed for object [aaa,bbb,ccc]
    at org.apache.ibatis.scripting.xmltags.OgnlCache.getValue(OgnlCache.java:45) ~[mybatis-3.2.8.jar:3.2.8]
    ... (more frames omitted) ...

The error occurs intermittently; most calls work fine, but occasional failures require deeper investigation.

Source Code Analysis

Investigation shows that OGNL expressions obtain methods via reflection and cache them in a static variable, which can cause concurrency issues when multiple threads access the cache.

Below is the caching logic (see the method org.apache.ibatis.ognl.OgnlRuntime#getMethods(java.lang.Class, boolean) for details).

The bug manifests when one thread sets a flag to true while another thread resets it to false before the method is invoked, leading to a failure.

The MyBatis issue tracker confirms this problem: https://github.com/mybatis/mybatis-3/pull/384.

The suggested fix is to upgrade MyBatis, but upgrading may not be feasible in a stable production codebase.

As a workaround, avoid using Arrays.asList (which returns a private inner class) in OGNL expressions. Instead, use Lists.newArrayList or other public‑method alternatives.

Summary

Problem: Non‑public methods or classes used in OGNL expressions can cause concurrency issues.

Solution 1: Upgrade MyBatis to a version where the bug is fixed.

Solution 2: Replace Arrays.asList with Lists.newArrayList or other public‑method collections to avoid the private inner‑class pitfall.