Add Java Stream API support

core/src/main/java/com/creditdatamw/zerocell/Reader.java

@@ -8,6 +8,7 @@
 import java.io.File;
 import java.util.List;
 import java.util.Objects;
+import java.util.stream.Stream;
 
 /**
  * Main API for ZeroCell
@@ -87,8 +88,14 @@ public ReaderBuilder<T> setRowNumber(int rowNumber) {
             return this;
         }
 
+        /**
+         * Processes the file
+         *
+         * @param <T>
+         * @return EntityHandler instance
+         */
         @SuppressWarnings("unchecked")
-        public <T> List<T> list() {
+        private <T> EntityHandler<T> processFile() {
             EntityHandler<T> entityHandler;
             if (!Objects.isNull(sheetName) && !Objects.isNull(columnMapping)) {
                 entityHandler = new EntityHandler(clazz, sheetName, columnMapping, skipHeaderRow, skipFirstNRows, maxRowNumber);
@@ -100,7 +107,25 @@ public <T> List<T> list() {
                 entityHandler = new EntityHandler(clazz, skipHeaderRow, skipFirstNRows, maxRowNumber);
             }
             entityHandler.process(file);
+            return entityHandler;
+        }
+
+        /**
+         * Reads the Entities from the Excel file and returns a list
+         * @return List of entities
+         */
+        public List<T> list() {
+            EntityHandler<T> entityHandler = processFile();
             return entityHandler.readAsList();
         }
+
+        /**
+         * Reads the Entities the Excel file and returns a Stream
+         * @return Stream of entities
+         */
+        public Stream<T> stream() {
+            EntityHandler<T> entityHandler = processFile();
+            return entityHandler.readAsStream();
+        }
     }
 }

core/src/main/java/com/creditdatamw/zerocell/handler/EntityExcelSheetHandler.java

@@ -15,6 +15,8 @@
 import java.io.File;
 import java.lang.reflect.Field;
 import java.util.*;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
 
 import static com.creditdatamw.zerocell.converter.ConverterUtils.convertValueToType;
 
@@ -24,7 +26,7 @@ final class EntityExcelSheetHandler<T> implements ZeroCellReader {
 
     private final ColumnInfo rowNumberColumn;
     private final Map<Integer, ColumnInfo> columns;
-    private final List<T> entities;
+    private Stream.Builder<T> streamBuilder;
     private final Converter NOOP_CONVERTER = new NoopConverter();
     private final Map<Integer, Converter> converters;
     private boolean isHeaderRow = false;
@@ -37,7 +39,7 @@ final class EntityExcelSheetHandler<T> implements ZeroCellReader {
         this.rowNumberColumn = rowNumberColumn;
         this.columns = columns;
         this.converters = cacheConverters();
-        this.entities = new ArrayList<>();
+        this.streamBuilder = Stream.builder();
     }
 
     private Map<Integer, Converter> cacheConverters() {
@@ -67,14 +69,19 @@ public List<T> read(File file, String sheet) {
          * We don't need to process the file here since that's
          * handled in {@link ReaderUtil} which MUST be used when using this class
          */
-        return Collections.unmodifiableList(this.entities);
+        return getEntityStream().collect(Collectors.toList());
+    }
+
+    public Stream<T> getEntityStream() {
+        return this.streamBuilder.build();
     }
 
     void clear() {
         this.currentRow = -1;
         this.currentCol = -1;
         this.cur = null;
-        this.entities.clear();
+        this.streamBuilder = null;
+        this.streamBuilder = Stream.builder();
     }
 
     @Override
@@ -114,7 +121,8 @@ public void endRow(int i) {
         }
 
         if (!Objects.isNull(cur)) {
-            this.entities.add(cur);
+            // this.entities.add(cur);
+            streamBuilder.add(cur);
             cur = null;
         }
     }

core/src/main/java/com/creditdatamw/zerocell/handler/EntityHandler.java

@@ -13,6 +13,7 @@
 import java.util.List;
 import java.util.Map;
 import java.util.Objects;
+import java.util.stream.Stream;
 
 import static com.creditdatamw.zerocell.column.ColumnMapping.parseColumnMappingFromAnnotations;
 
@@ -116,6 +117,10 @@ public List<T> readAsList() {
         return list;
     }
 
+    public Stream<T> readAsStream() {
+        return this.entitySheetHandler.getEntityStream();
+    }
+
     public void process(File file) throws ZeroCellException {
         ReaderUtil.process(file, sheetName, this.entitySheetHandler);
     }

core/src/test/java/com/creditdatamw/zerocell/TestReader.java

@@ -13,6 +13,7 @@
 import java.sql.Date;
 import java.time.LocalDate;
 import java.util.List;
+import java.util.Optional;
 
 import static org.junit.Assert.*;
 
@@ -42,6 +43,17 @@ public void testShouldExtractPeopleFromFile() {
         assertEquals(1, zikani.getRowNumber());
         assertEquals("Zikani", zikani.getFirstName());
     }
+    @Test
+    public void testShouldReturnStream() {
+        Optional<Person> zikani = Reader.of(Person.class)
+            .from(new File("src/test/resources/test_people.xlsx"))
+            .sheet("uploads")
+            .stream()
+            .findFirst();
+        assertTrue(zikani.isPresent());
+        assertEquals(1, zikani.get().getRowNumber());
+        assertEquals("Zikani", zikani.get().getFirstName());
+    }
 
     @Test
     public void testShouldSkipFirst3RowsFromFile() {