Question

With API16 the new WAL (Write Ahead Logging) was introduced in Androids SQLiteDatabase class. I would like to test if WAL is enabled for a SQLite database. The app runs on older Android releases too, so I need a wrapper class for these new functions in SQLiteDatabase. The functions are:

• public boolean isWriteAheadLoggingEnabled()
• public boolean enableWriteAheadLogging()
• public void disableWriteAheadLogging ()

In the Android Developer Blog I did find an article for a wrapper class that wraps new classes. What I didn’t find is a wrapper for new methods in an already existing class. How should I do that?

Answer 1

The constructor for SQLiteDatabase is private so your’re not going to be able to extend it and add “wrappers” to the class itself. You can however just write a “helper” wrapper like so:

public class WALWrapper {
    private boolean mAvailable;
    private Method mIsWriteAheadLoggingEnabled;
    private Method mEnableWriteAheadLogging;
    private Method mDisableWriteAheadLogging;
    private final SQLiteDatabase mDb;

    public WALWrapper(SQLiteDatabase db) {
        mDb = db;
        mAvailable = false;
        try {
            mIsWriteAheadLoggingEnabled =
                    SQLiteDatabase.class.getMethod("isWriteAheadLoggingEnabled");
            mEnableWriteAheadLogging =
                    SQLiteDatabase.class.getMethod("enableWriteAheadLogging");
            mDisableWriteAheadLogging =
                    SQLiteDatabase.class.getMethod("disableWriteAheadLogging");
            mAvailable = true;
        } catch (NoSuchMethodException e) {
        }
    }

    /**
     * Returns <code>true</code> if the {@link #isWriteAheadLoggingEnabled()},
     * {@link #enableWriteAheadLogging()} and {@link #disableWriteAheadLogging()}
     * are available.
     * @return <code>true</code> if the WALWrapper is functional, <code>false</code>
     *  otherwise.
     */
    public boolean isWALAvailable() {
        return mAvailable;
    }

    public boolean isWriteAheadLoggingEnabled() {
        boolean result = false;
        if (mIsWriteAheadLoggingEnabled != null) {
            try {
                result = (Boolean) mIsWriteAheadLoggingEnabled.invoke(mDb);
            } catch (IllegalArgumentException e) {
            } catch (IllegalAccessException e) {
            } catch (InvocationTargetException e) {
            }
        }
        return result;
    }

    public boolean enableWriteAheadLogging() {
        boolean result = false;
        if (mEnableWriteAheadLogging != null) {
            try {
                result = (Boolean) mEnableWriteAheadLogging.invoke(mDb);
            } catch (IllegalArgumentException e) {
            } catch (IllegalAccessException e) {
            } catch (InvocationTargetException e) {
            }
        }
        return result;
    }

    public void disableWriteAheadLogging() {
        if (mDisableWriteAheadLogging != null) {
            try {
                mDisableWriteAheadLogging.invoke(mDb);
            } catch (IllegalArgumentException e) {
            } catch (IllegalAccessException e) {
            } catch (InvocationTargetException e) {
            }
        }
    }
}