java-native-access/jna · error · Error

Exception reading field '" + field.getName() + "' in " +…

Error message

Exception reading field '" + field.getName() + "' in " + getClass()

What it means

Structure.getFieldValue(Field) invokes Field.get(this) reflectively; any failure (e.g. IllegalAccessException on inaccessible fields in restrictive environments) is rethrown as a java.lang.Error wrapping the original exception. It signals the VM refused reflective access to a declared structure field.

Solutions

1. Ensure the field is accessible: make it public in the Structure subclass or rely on JNA's own setAccessible call succeeding
2. Check for a SecurityManager or custom policy blocking reflect access and grant ReflectPermission("suppressAccessChecks") if acceptable
3. Disable aggressive obfuscation (keep Structure subclass field names in ProGuard/R8 rules)
4. If the wrapped cause is the real problem, fix according to the cause (e.g. IllegalAccessException) rather than catching the Error

Example fix

// proguard-rules.pro
-keepclassmembers class * extends com.sun.jna.Structure {
    <fields>;
}

try { field.setAccessible(true); } catch (SecurityException e) { /* reflective access unavailable: fail fast */ }

try { return struct.readField(field); } catch (Error e) { Throwable cause = e.getCause(); log.severe("reflective read failed: " + cause); throw new RuntimeException(cause); }

When it happens

Trigger: Reflective read of a private/package-private field without setAccessible(true) succeeding, e.g. under a SecurityManager or restrictive classloader; field removed/changed by bytecode transformation; on some J2ME/Android-like VMs where access override is unsupported.

Common situations: Running under OSGi or app-server classloaders with strict access rules; obfuscated/ProGuard-shrunk builds renaming fields; embedding JNA in a restricted JVM (J2ME, some WebStart setups).

Understand the failure class

Background: "This is a bug, please report it": internal invariant violations, unreachable panics, and SNH errors explained — this error's family across 47 libraries.

Related errors

• Unexpectedly unable to write to field '" + field.getName()…
• Could not access instance of
• Attempt to write to read-only field '" + field.getName() +…
• Callback method is inaccessible, make sure the interface is…
• Can't create an instance of

AI-assisted analysis of java-native-access/jna@d036ad9781 (2026-09-12). Data as JSON: /api/errors/3b8cb42df83141a2. Report an issue: GitHub.

Appendix: source

Thrown at src/com/sun/jna/Structure.java:657

    public Object readField(String name) {
        ensureAllocated();
        StructField f = fields().get(name);
        if (f == null)
            throw new IllegalArgumentException("No such field: " + name);
        return readField(f);
    }

    /** Obtain the value currently in the Java field.  Does not read from
     * native memory.
     * @param field field to look up
     * @return current field value (Java-side only)
     */
    Object getFieldValue(Field field) {
        try {
            return field.get(this);
        }
        catch (Exception e) {
            throw new Error("Exception reading field '" + field.getName() + "' in " + getClass(), e);
        }
    }

    /**
     * @param field field to set
     * @param value value to set
     */
    void setFieldValue(Field field, Object value) {
        setFieldValue(field, value, false);
    }

    private void setFieldValue(Field field, Object value, boolean overrideFinal) {

        try {
            field.set(this, value);
        }
        catch(IllegalAccessException e) {
            int modifiers = field.getModifiers();

View on GitHub (pinned to d036ad9781)