alibaba/arthas · warning · IllegalAccessError

By default, strict mode is true, not allowed to set object…

Error message

By default, strict mode is true, not allowed to set object properties. Want to set object properties, execute `options strict false`

What it means

Thrown as IllegalAccessError by ArthasObjectPropertyAccessor.setPossibleProperty when GlobalOptions.strict is true (the default) and an OGNL expression tries to SET an object property (write). This is a deliberate safety guard: out-of-the-box Arthas forbids OGNL writes to objects to prevent accidental mutation of the live target application. The message itself (GlobalOptions.STRICT_MESSAGE) instructs the user how to opt out.

Solutions

Explicitly disable strict mode: run `options strict false` before the mutating expression.
Re-evaluate whether you really need to write — prefer read-only diagnostics; if you must mutate, accept the risk consciously.
Re-enable strict after: `options strict true`.

Example fix

// before
ognl '#this.enabled = true'   // throws under strict mode

// after
options strict false
ognl '#this.enabled = true'
options strict true

Defensive patterns

Strategy: validation

Validate before calling

if (GlobalOptions.strict && expressionIsWrite(ognlExpr)) {
    // either run `options strict false` or refrain from writing
}

Type guard

static boolean isStrictWriteBlocked() { return GlobalOptions.strict; }

Try / catch

try {
    Object r = ognlEngine.get/setValue(...);
} catch (IllegalAccessError e) {
    if (e.getMessage().equals(GlobalOptions.STRICT_MESSAGE)) {
        // instruct user to `options strict false` if write is intentional
    }
}

Prevention

Prefer read-only OGNL expressions for diagnostics.
Consciously toggle `options strict false` only when mutation is intended, then re-enable.
Document which expressions write so reviewers can catch accidental mutations.

When it happens

Trigger: Evaluate an OGNL expression that assigns to a property — e.g. '#this.field = x', 'target.foo = bar', or any lvalue assignment in watch/trace/ognl — while GlobalOptions.strict is at its default true.

Common situations: User attempts to mutate target state via ognl/watch without knowing strict mode is on; scripted diagnostics that try to flip a flag on the target; migrating from an older Arthas where strict was not enforced.

Related errors

AI-assisted analysis of alibaba/arthas@21cf2e9ba5 (2026-08-14). Data as JSON: /api/errors/c7e203db3011be52. Report an issue: GitHub.

Appendix: source

Thrown at core/src/main/java/com/taobao/arthas/core/command/express/ArthasObjectPropertyAccessor.java:18

package com.taobao.arthas.core.command.express;

import java.util.Map;

import com.taobao.arthas.core.GlobalOptions;

import ognl.ObjectPropertyAccessor;
import ognl.OgnlException;

/**
 * @author hengyunabc 2022-03-24
 */
public class ArthasObjectPropertyAccessor extends ObjectPropertyAccessor {

    @Override
    public Object setPossibleProperty(Map context, Object target, String name, Object value) throws OgnlException {
        if (GlobalOptions.strict) {
            throw new IllegalAccessError(GlobalOptions.STRICT_MESSAGE);
        }
        return super.setPossibleProperty(context, target, name, value);
    }

}

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