VUFIND-1342 Have our SolrFieldIterators implement Iterator and Iterable

Also modifies PrintBrowseHeadings to take advantage of the Iterable.

src/main/java/org/vufind/solr/indexing/PrintBrowseHeadings.java

@@ -51,8 +51,7 @@ private void loadHeadings(SolrFieldIterator fieldIterator,
                               Predicate predicate)
     throws Exception
     {
-        BrowseEntry h;
-        while ((h = fieldIterator.next()) != null) {
+        for (BrowseEntry h : fieldIterator) {
             // We use a byte array for the sort key instead of a string to ensure
             // consistent sorting even if the index tool and browse handler are running
             // with different locale settings. Using strings results in less predictable

src/main/java/org/vufind/solr/indexing/SolrFieldIterator.java

@@ -3,7 +3,9 @@
 import java.io.File;
 import java.io.IOException;
 import java.util.ArrayList;
+import java.util.Iterator;
 import java.util.List;
+import java.util.NoSuchElementException;
 
 import org.apache.lucene.index.CompositeReader;
 import org.apache.lucene.index.DirectoryReader;
@@ -22,7 +24,7 @@
 import org.vufind.util.NormalizerFactory;
 
 
-public class SolrFieldIterator implements AutoCloseable
+public class SolrFieldIterator implements AutoCloseable, Iterator<BrowseEntry>, Iterable<BrowseEntry>
 {
     protected CompositeReader reader;
     protected IndexSearcher searcher;
@@ -34,6 +36,8 @@ public class SolrFieldIterator implements AutoCloseable
 
     TermsEnum tenum = null;
 
+    private BrowseEntry nextEntry = null;
+    private boolean exhausted = false;
 
     public SolrFieldIterator(String indexPath, String field) throws Exception
     {
@@ -83,7 +87,7 @@ private boolean termExists(String t)
     //
     // If there's no currently selected TermEnum, create one from the reader.
     //
-    public BrowseEntry next() throws Exception
+    protected BrowseEntry readNext() throws IOException
     {
         for (;;) {
             if (tenum == null) {
@@ -123,4 +127,52 @@ public BrowseEntry next() throws Exception
             // Try the next term
         }
     }
+
+
+    public void tryReadNext() {
+        if (nextEntry != null) {
+            // Already have one
+            return;
+        }
+
+        if (exhausted) {
+            // Nothing more to read
+        }
+
+        try {
+            nextEntry = readNext();
+        } catch (IOException e) {
+            throw new RuntimeException(e);
+        }
+
+        if (nextEntry == null) {
+            exhausted = true;
+        }
+    }
+
+    @Override
+    public BrowseEntry next() {
+        tryReadNext();
+
+        if (nextEntry == null) {
+            throw new NoSuchElementException();
+        }
+
+        BrowseEntry result = nextEntry;
+        nextEntry = null;
+
+        return result;
+    }
+
+    @Override
+    public boolean hasNext() {
+        tryReadNext();
+
+        return nextEntry != null;
+    }
+
+    @Override
+    public Iterator<BrowseEntry> iterator() {
+        return this;
+    }
 }

src/main/java/org/vufind/solr/indexing/StoredFieldIterator.java

@@ -3,6 +3,7 @@
 // Build a browse list by walking the docs in an index and extracting sort key
 // and values from a pair of stored fields.
 import java.io.File;
+import java.io.IOException;
 import java.util.HashSet;
 import java.util.LinkedList;
 import java.util.Set;
@@ -56,8 +57,7 @@ public StoredFieldIterator(String indexPath, String field) throws Exception
     }
 
 
-    private void loadDocument(IndexReader reader, int docid)
-    throws Exception
+    private void loadDocument(IndexReader reader, int docid) throws IOException
     {
         Document doc = reader.storedFields().document(currentDoc, fieldSelection);
 
@@ -88,7 +88,7 @@ private void loadDocument(IndexReader reader, int docid)
     }
 
 
-    public BrowseEntry next() throws Exception
+    protected BrowseEntry readNext() throws IOException
     {
         while (buffer.isEmpty()) {
             if (currentDoc < reader.maxDoc()) {