{"record":{"id":"82833d51ac094fc4","repo":"alibaba/canal","slug":"cannot-get-field","errorCode":null,"errorMessage":"Cannot get field: '{}' @ {}","messagePattern":"Cannot get field: '(.+?)' @ (.+?)","errorType":"validation","errorClass":"IllegalArgumentException","httpStatus":null,"severity":"error","filePath":"dbsync/src/main/java/com/taobao/tddl/dbsync/binlog/DirectLogFetcher.java","lineNumber":140,"sourceCode":"        } catch (NoSuchMethodException e) {\r\n            throw new IllegalArgumentException(\"No such method: \\'\" + name + \"\\' @ \" + objClazz.getName(), e);\r\n        } catch (IllegalAccessException e) {\r\n            throw new IllegalArgumentException(\"Cannot invoke method: \\'\" + name + \"\\' @ \" + objClazz.getName(), e);\r\n        } catch (InvocationTargetException e) {\r\n            throw new IllegalArgumentException(\"Invoke method failed: \\'\" + name + \"\\' @ \" + objClazz.getName(),\r\n                e.getTargetException());\r\n        }\r\n    }\r\n\r\n    private static final Object getDeclaredField(Object obj, Class<?> objClazz, String name) {\r\n        try {\r\n            Field field = objClazz.getDeclaredField(name);\r\n            field.setAccessible(true);\r\n            return field.get(obj);\r\n        } catch (NoSuchFieldException e) {\r\n            throw new IllegalArgumentException(\"No such field: \\'\" + name + \"\\' @ \" + objClazz.getName(), e);\r\n        } catch (IllegalAccessException e) {\r\n            throw new IllegalArgumentException(\"Cannot get field: \\'\" + name + \"\\' @ \" + objClazz.getName(), e);\r\n        }\r\n    }\r\n\r\n    /**\r\n     * Connect MySQL master to fetch binlog.\r\n     */\r\n    public void open(Connection conn, String fileName, final int serverId) throws IOException {\r\n        open(conn, fileName, BIN_LOG_HEADER_SIZE, serverId, false);\r\n    }\r\n\r\n    /**\r\n     * Connect MySQL master to fetch binlog.\r\n     */\r\n    public void open(Connection conn, String fileName, final int serverId, boolean nonBlocking) throws IOException {\r\n        open(conn, fileName, BIN_LOG_HEADER_SIZE, serverId, nonBlocking);\r\n    }\r\n\r\n    /**\r","sourceCodeStart":122,"sourceCodeEnd":158,"githubUrl":"https://github.com/alibaba/canal/blob/87be50e87686a3e8af08c368d0e1ffd1f59eb04a/dbsync/src/main/java/com/taobao/tddl/dbsync/binlog/DirectLogFetcher.java#L122-L158","documentation":"Thrown by getDeclaredField() when Field.get raises IllegalAccessException despite the helper calling setAccessible(true). This points to a hard access denial: a JPMS module that is not open to dbsync, or a SecurityManager refusing the suppress-accesschecks permission.","triggerScenarios":"getDeclaredField locates the field and calls setAccessible(true), but the JVM denies reflective read access - a module is closed (not open) to dbsync, or a SecurityManager lacks ReflectPermission(\"suppressAccessChecks\").","commonSituations":"Running on Java 9+ where the mysql driver module is not opened to the unnamed module dbsync lives in; a custom SecurityManager / security policy in the app server; an agent that blocks accessibility overrides.","solutions":["Add --add-opens flags opening the mysql driver's package to the application (e.g. --add-opens module/package=ALL-UNNAMED).","Relax or remove the SecurityManager / security policy if reflective access to the driver is intended.","Run dbsync on the classpath (unnamed module) rather than as a named module so opens are not required.","Pin a driver + JVM combination known to allow the field access this fork needs."],"exampleFix":"// before - JVM launch with module access denied\njava -jar dbsync-app.jar\n\n// after - open the driver package to the unnamed module\njava --add-opens java.base/java.lang=ALL-UNNAMED \\\n     --add-opens com.mysql.cj/com.mysql.cj.jdbc=ALL-UNNAMED \\\n     -jar dbsync-app.jar","handlingStrategy":"validation","validationCode":"// Detect module/SecurityManager blocking before relying on reflection\njava.lang.reflect.Field f = connClazz.getDeclaredField(\"io\");\ntry { f.setAccessible(true); }\ncatch (SecurityException se) {\n    throw new IllegalStateException(\"JVM denies reflective field access - open the module or drop SecurityManager\", se);\n}","typeGuard":null,"tryCatchPattern":"try { fetcher.open(conn, file, pos, serverId, false); }\ncatch (IllegalArgumentException e) {\n    if (e.getCause() instanceof IllegalAccessException)\n        throw new IOException(\"module/policy blocks driver field access\", e);\n    throw e;\n}","preventionTips":["Add --add-opens for the mysql driver's package to the JVM on Java 9+.","Avoid running under a SecurityManager that forbids suppressAccessChecks.","Prefer a classpath (unnamed-module) deployment for dbsync."],"tags":["binlog","reflection","module-system","securitymanager"],"backgroundTag":null,"analyzedSha":"87be50e87686a3e8af08c368d0e1ffd1f59eb04a","analyzedAt":"2026-08-14T04:30:11.918Z","schemaVersion":2},"datasetVersion":"2026-08-14T05:17:29.042Z"}