alibaba/druid · error · IllegalArgumentException

{className}

Error message

{className}

What it means

DruidAbstractDataSource.setStatLoggerClassName reflectively loads, instantiates, and casts a class to DruidDataSourceStatLogger. Any failure (ClassNotFoundException, InstantiationException, IllegalAccessException, ClassCastException, or a constructor-thrown exception) is wrapped as IllegalArgumentException(className, e) - note the message is just the class name and the real cause is in the exception's cause.

Source

Thrown at core/src/main/java/com/alibaba/druid/pool/DruidAbstractDataSource.java:343

        return keepConnectionUnderlyingTransactionIsolation;
    }

    public void setKeepConnectionUnderlyingTransactionIsolation(boolean keepConnectionUnderlyingTransactionIsolation) {
        this.keepConnectionUnderlyingTransactionIsolation = keepConnectionUnderlyingTransactionIsolation;
    }

    public DruidDataSourceStatLogger getStatLogger() {
        return statLogger;
    }

    public void setStatLoggerClassName(String className) {
        Class<?> clazz;
        try {
            clazz = Class.forName(className);
            DruidDataSourceStatLogger statLogger = (DruidDataSourceStatLogger) clazz.newInstance();
            this.setStatLogger(statLogger);
        } catch (Exception e) {
            throw new IllegalArgumentException(className, e);
        }
    }

    public void setStatLogger(DruidDataSourceStatLogger statLogger) {
        this.statLogger = statLogger;
    }

    public long getTimeBetweenLogStatsMillis() {
        return timeBetweenLogStatsMillis;
    }

    public void setTimeBetweenLogStatsMillis(long timeBetweenLogStatsMillis) {
        this.timeBetweenLogStatsMillis = timeBetweenLogStatsMillis;
    }

    public boolean isOracle() {
        return isOracle;
    }

View on GitHub (pinned to fa8dc99126)

Solutions

1. Confirm the class is on the classpath and implements com.alibaba.druid.stat.DruidDataSourceStatLogger.
2. Ensure a public no-arg constructor exists and the class is concrete/public.
3. Prefer setStatLogger(new MyStatLogger()) to get a compile-time type check instead of reflective loading.
4. Read IllegalArgumentException.getCause() to identify ClassNotFoundException vs ClassCastException vs InstantiationException.

Example fix

// before
// ds.setStatLoggerClassName("com.example.MyStatLogger"); // reflective, runtime-only

// after
// ds.setStatLogger(new com.example.MyStatLogger()); // compile-time checked

Class<?> c = Class.forName(className);
if (!com.alibaba.druid.stat.DruidDataSourceStatLogger.class.isAssignableFrom(c))
    throw new IllegalStateException(className + " is not a DruidDataSourceStatLogger");
com.alibaba.druid.stat.DruidDataSourceStatLogger probe =
    (com.alibaba.druid.stat.DruidDataSourceStatLogger) c.newInstance();

static boolean isValidStatLoggerClass(String name) {
    try {
        Class<?> c = Class.forName(name);
        return com.alibaba.druid.stat.DruidDataSourceStatLogger.class.isAssignableFrom(c)
            && !java.lang.reflect.Modifier.isAbstract(c.getModifiers());
    } catch (Throwable t) { return false; }
}

try {
    ds.setStatLoggerClassName(className);
} catch (IllegalArgumentException e) {
    // e.getMessage() == className; e.getCause() tells you which: CNFE/CCE/IE/IAE
    // prefer ds.setStatLogger(new MyStatLogger()) instead
    throw e;
}

When it happens

Trigger: Calling setStatLoggerClassName("foo.Bar") where Bar is not on the classpath, is abstract/inaccessible, does not implement DruidDataSourceStatLogger, or its constructor throws.

Common situations: Typo in the stat logger class name; the logger class lives in a JAR not on the datasource's classloader; providing a class that implements a different Druid version's DruidDataSourceStatLogger interface.

Related errors

• create exceptionSorter error
• load managed jdbc driver event listener error. {filterName}
• ConfigLoader only support DruidDataSource
• Config DataSource error.
• maxEvictableIdleTimeMillis must be grater than minEvictableI

AI-assisted analysis of alibaba/druid@fa8dc99126 (2026-08-14). Data as JSON: /api/errors/eddfbf56e63c6a97. Report an issue: GitHub.