Serializer serializer = new Persister();
File fFoo= new File(context.getFilesDir(), "foo.xml");
serializer.write(fooObject, fFoo);

Stack trace: java.io.FileNotFoundException: /data/data/net.foo.appfoo/files/foo.xml: open failed: EROFS (Read-only file system)
    at libcore.io.IoBridge.open(IoBridge.java:460)
    at java.io.FileOutputStream.<init>(FileOutputStream.java:88)
    at java.io.FileOutputStream.<init>(FileOutputStream.java:73)
    at org.simpleframework.xml.core.Persister.write(SourceFile:1198)