1 files changed, 40 insertions, 19 deletions

diff --git a/src/io/DataWriter.java b/src/io/DataWriter.java
index 252c50c..d06e283 100644
--- a/src/io/DataWriter.java
+++ b/src/io/DataWriter.java
@@ -48,24 +48,30 @@ public class DataWriter implements ResultListener {
     public final static String CFG_TWEETS_FILENAME = "tweets-filename";
 
     /**
-     * Opens a stream to every single file that data will be streamed to.
+     * Creates an instance, specifying the profile and file names to which
+     * tweets and users are written.
      *
      * @param profilesName The file to write the profiles to.
      * @param tweetsName The file to write the tweets to.
-     * @throws java.io.IOException if the files cannot be read or written.
      */
-    public DataWriter(final String profilesName, final String tweetsName)
-            throws IOException {
+    public DataWriter(final String profilesName, final String tweetsName) {
         m_profile = getStore(profilesName);
-        try {
-            m_profileIdSet = readIds(m_profile);
-        } catch (IOException ex) {
-            m_profile.close();
-            throw ex;
-        }
+        m_profileIdSet = new HashSet<>();
         m_tweet = getStore(tweetsName);
+        m_tweetIdSet = new HashSet<>();
+    }
+
+    /**
+     * Opens a stream to every single file that data will be streamed to.
+     *
+     * @throws java.io.IOException if the files cannot be read or written.
+     */
+    public void open() throws IOException {
         try {
-            m_tweetIdSet = readIds(m_tweet);
+            m_profile.open();
+            m_tweet.open();
+            readIds(m_profileIdSet, m_profile);
+            readIds(m_tweetIdSet, m_tweet);
         } catch (IOException ex) {
             m_profile.close();
             m_tweet.close();
@@ -78,9 +84,8 @@ public class DataWriter implements ResultListener {
      *
      * @param filename File to read/write.
      * @return A Store instance providing read and write access.
-     * @throws IOException if the target file cannot be read or written.
      */
-    protected Store getStore(String filename) throws IOException {
+    protected Store getStore(String filename) {
         return new SimpleFileStore(filename);
     }
 
@@ -106,8 +111,7 @@ public class DataWriter implements ResultListener {
      * @param is An input stream that provides JSON objects.
      * @return The set of ids, may be empty if the fill does not exist.
      */
-    private Set<Long> readIds(Store store) throws IOException {
-        Set<Long> idSet = new HashSet<>();
+    private void readIds(Set<Long> idSet, Store store) throws IOException {
         InputStream is = null;
         try {
             is = store.getInputStream();
@@ -128,7 +132,6 @@ public class DataWriter implements ResultListener {
         } finally {
             IOUtils.closeQuietly(is);
         }
-        return idSet;
     }
 
     /**
@@ -178,11 +181,22 @@ public class DataWriter implements ResultListener {
         }
 
         /**
+         * Opens the writable stream (if not open yet), must be called before
+         * writing a stream.
+         *
+         * @throws IOException
+         */
+        abstract public void open() throws IOException;
+
+        /**
          * Properly closes a file, flushing any buffers.
          */
         public void close() {
             try {
-                os.close();
+                if (os != null) {
+                    os.close();
+                    os = null;
+                }
             } catch (IOException ex) {
                 Logger.getLogger(getClass().getName()).log(Level.WARNING,
                         "Could not close " + getFileName(), ex);
@@ -193,6 +207,7 @@ public class DataWriter implements ResultListener {
          * Returns a previously opened writable file stream.
          *
          * @return A stream to which JSON objects can be written (one per line).
+         * If no writable stream is open, {@code null} is returned.
          */
         public OutputStream getOutputStream() {
             return os;
@@ -209,9 +224,15 @@ public class DataWriter implements ResultListener {
 
     class SimpleFileStore extends Store {
 
-        SimpleFileStore(String filename) throws FileNotFoundException {
+        SimpleFileStore(String filename) {
             super(filename);
-            os = new FileOutputStream(getFileName(), true);
+        }
+
+        @Override
+        public void open() throws IOException {
+            if (os == null) {
+                os = new FileOutputStream(getFileName(), true);
+            }
         }
 
         @Override