private RAMDirectory createRAMDirectory() {
RAMDirectory directory = new RAMDirectory();
IndexWriter writer = null;
try {
writer = new IndexWriter(directory, new SimpleAnalyzer(), true);
Document document1 = new Document();
document1.add(new Field("id", "1", Field.Store.YES, Field.Index.UN_TOKENIZED));
writer.addDocument(document1);
Document document2 = new Document();
document2.add(new Field("id", "2", Field.Store.YES, Field.Index.UN_TOKENIZED));