#20 absolute positioning added

Author: Vedran

README.md

@@ -33,7 +33,7 @@ Latest version [here](https://github.com/Vatavuk/vgv-xls/releases)
 Java version required: 1.8+.
 
 
-## Example
+## Create spreadsheet
 ```java
 new XsWorkbook(
     new XsSheet(
@@ -56,13 +56,26 @@ new XsWorkbook(
                     )
                 )
             )
-            .with(new XsProps<>(new Height((short) 20)))
+            .with(new XsProps<>(new Height((short) 500)))
     )
 ).saveTo("Test.xlsx");
 ```
 This is how the result looks like:
 <img src="https://i.imgur.com/3hUJkJ2.png"/>
 
+## Read and modify spreadsheet
+Read from "Test.xlsx" file and modify cell int the second row/first column.
+```java
+new XsWorkbook("Test.xlsx")
+    .with(new XsSheet.ReadFrom(0)
+        .with(
+            new XsRow(2,
+                new TextCell(0, "UPDATED")
+            )
+        )
+    ).saveTo("Updated.xlsx");
+```
+
 ## Custom styles
 You can create custom cells/rows/sheets:
 ```java

src/main/java/com/vgv/xls/ECell.java

@@ -38,28 +38,6 @@
 @SuppressWarnings("PMD.AvoidUsingShortType")
 public interface ECell {
 
-    /**
-     * Empty cell.
-     */
-    ECell EMPTY = new ECell() {
-        @Override
-        public Cell attachTo(final Row row) {
-            final short index = row.getLastCellNum();
-            final int position;
-            if ((int) index < 0) {
-                position = 0;
-            } else {
-                position = (int) index;
-            }
-            return row.createCell(position);
-        }
-
-        @Override
-        public ECell with(final Style style) {
-            return new ECell.WithStyle(this, style);
-        }
-    };
-
     /**
      * Attach cell to a row.
      * @param row Row

src/main/java/com/vgv/xls/ERow.java

@@ -55,13 +55,6 @@ public interface ERow {
      */
     ERow with(ECell... cells);
 
-    /**
-     * Add cell to the row.
-     * @param cell Cell
-     * @return Row
-     */
-    ERow with(ECell cell);
-
     /**
      * Add cells to the row.
      * @param cells Cells

src/main/java/com/vgv/xls/ESheet.java

@@ -23,6 +23,7 @@
  */
 package com.vgv.xls;
 
+import java.io.IOException;
 import org.apache.poi.ss.usermodel.Sheet;
 import org.apache.poi.ss.usermodel.Workbook;
 
@@ -38,8 +39,9 @@ public interface ESheet {
      * Attach sheet to a workbook.
      * @param workbook Workbook
      * @return Sheet
+     * @throws IOException If fails
      */
-    Sheet attachTo(Workbook workbook);
+    Sheet attachTo(Workbook workbook) throws IOException;
 
     /**
      * Add row to the sheet.

src/main/java/com/vgv/xls/XsRow.java

@@ -34,15 +34,19 @@
  *
  * <p>This is how you can use it:</p>
  *
- *     new XsRow(new TextCell("txt"), new NumberCell(2))
- *
+ * new XsRow(new TextCell("txt"), new NumberCell(2))
  * @author Vedran Grgo Vatavuk (123vgv@gmail.com)
  * @version $Id$
  * @since 0.1
  */
 @SuppressWarnings("PMD.TooManyMethods")
 public final class XsRow implements ERow {
 
+    /**
+     * Row position.
+     */
+    private final int index;
+
     /**
      * Array of cells.
      */
@@ -56,17 +60,36 @@ public XsRow(final ECell... elements) {
         this(new Array<>(elements));
     }
 
+    /**
+     * Ctor.
+     * @param position Row position
+     * @param elements Cells
+     */
+    public XsRow(final int position, final ECell... elements) {
+        this(position, new Array<>(elements));
+    }
+
     /**
      * Ctor.
      * @param elements Cells
      */
     public XsRow(final Iterable<ECell> elements) {
+        this(-1, new Array<>(elements));
+    }
+
+    /**
+     * Ctor.
+     * @param position Row position
+     * @param elements Cells
+     */
+    public XsRow(final int position, final Iterable<ECell> elements) {
+        this.index = position;
         this.cells = new Array<>(elements);
     }
 
     @Override
     public Row attachTo(final Sheet sheet) {
-        final Row row = sheet.createRow(sheet.getLastRowNum() + 1);
+        final Row row = this.createRow(sheet);
         for (final ECell cell : this.cells) {
             cell.attachTo(row);
         }
@@ -87,11 +110,6 @@ public ERow with(final ECell... elements) {
         return new XsRow(this.cells.with(new Array<>(elements)));
     }
 
-    @Override
-    public ERow with(final ECell cell) {
-        return new XsRow(this.cells.with(cell));
-    }
-
     @Override
     public ERow with(final ECells elements) {
         return new XsRow(this.cells.with(elements.asArray()));
@@ -103,6 +121,24 @@ public XsRow.WithProps with(final Props<Row> props) {
         return new XsRow.WithProps(this, props);
     }
 
+    /**
+     * Create new row.
+     * @param sheet Sheet
+     * @return Row Row
+     */
+    private Row createRow(final Sheet sheet) {
+        Row row;
+        if (this.index == -1) {
+            row = sheet.createRow(sheet.getLastRowNum() + 1);
+        } else {
+            row = sheet.getRow(this.index);
+            if (row == null) {
+                row = sheet.createRow(this.index);
+            }
+        }
+        return row;
+    }
+
     /**
      * Row with additional properties.
      */
@@ -145,11 +181,6 @@ public ERow with(final ECell... cells) {
             return this.origin.with(cells);
         }
 
-        @Override
-        public ERow with(final ECell cell) {
-            return this.origin.with(cell);
-        }
-
         @Override
         public ERow with(final ECells cells) {
             return this.origin.with(cells);

src/main/java/com/vgv/xls/XsSheet.java

@@ -24,10 +24,13 @@
 package com.vgv.xls;
 
 import com.jcabi.immutable.Array;
+import java.io.IOException;
 import java.util.ArrayList;
 import java.util.List;
 import org.apache.poi.ss.usermodel.Sheet;
 import org.apache.poi.ss.usermodel.Workbook;
+import org.cactoos.Func;
+import org.cactoos.func.IoCheckedFunc;
 
 /**
  * Sheet in an excel table.
@@ -154,7 +157,7 @@ public WithProps(final ESheet sheet, final Props<Sheet> properties) {
         }
 
         @Override
-        public Sheet attachTo(final Workbook workbook) {
+        public Sheet attachTo(final Workbook workbook) throws IOException {
             final Sheet sheet = this.origin.attachTo(workbook);
             this.props.accept(sheet);
             return sheet;
@@ -170,4 +173,73 @@ public ESheet with(final Style style) {
             return this.origin.with(style);
         }
     }
+
+    /**
+     * Read sheet from existing one by title or index.
+     */
+    public static final class ReadFrom implements ESheet {
+
+        /**
+         * Func.
+         */
+        private final Func<Workbook, Sheet> func;
+
+        /**
+         * Array of rows.
+         */
+        private final Array<ERow> rows;
+
+        /**
+         * Ctor.
+         * @param title Title
+         */
+        public ReadFrom(final String title) {
+            this(workbook -> workbook.getSheet(title), new Array<>());
+        }
+
+        /**
+         * Ctor.
+         * @param index Index
+         */
+        public ReadFrom(final int index) {
+            this(workbook -> workbook.getSheetAt(index), new Array<>());
+        }
+
+        /**
+         * Ctor.
+         * @param function Function
+         * @param elements Elements
+         */
+        public ReadFrom(final Func<Workbook, Sheet> function,
+            final Iterable<ERow> elements) {
+            this.func = function;
+            this.rows = new Array<>(elements);
+        }
+
+        @Override
+        public Sheet attachTo(final Workbook workbook) throws IOException {
+            final Sheet sheet = new IoCheckedFunc<>(this.func).apply(workbook);
+            if (sheet == null) {
+                throw new IOException("Sheet not found on specified index");
+            }
+            for (final ERow row : this.rows) {
+                row.attachTo(sheet);
+            }
+            return sheet;
+        }
+
+        @Override
+        public ESheet with(final ERow row) {
+            return new XsSheet.ReadFrom(this.func, this.rows.with(row));
+        }
+
+        @Override
+        public ESheet with(final Style style) {
+            final List<ERow> elements = new ArrayList<>(this.rows.size());
+            for (final ERow row : this.rows) {
+                elements.add(row.with(style));
+            }
+            return new XsSheet.ReadFrom(this.func, elements);
+        }
+    }
 }

src/main/java/com/vgv/xls/XsWorkbook.java

@@ -160,8 +160,9 @@ public EWorkbook with(final Style style) {
     /**
      * Attach sheets.
      * @param wbook Workbook
+     * @throws IOException If fails
      */
-    private void attachSheets(final Workbook wbook) {
+    private void attachSheets(final Workbook wbook) throws IOException {
         for (final ESheet sheet : this.sheets) {
             sheet.attachTo(wbook);
         }

src/main/java/com/vgv/xls/cells/CalendarCell.java

@@ -23,7 +23,6 @@
  */
 package com.vgv.xls.cells;
 
-import com.vgv.xls.ECell;
 import java.util.Calendar;
 import org.apache.poi.ss.usermodel.Cell;
 import org.apache.poi.ss.usermodel.Row;
@@ -36,6 +35,11 @@
  */
 public final class CalendarCell extends AbstractStyleableCell {
 
+    /**
+     * Cell position.
+     */
+    private final int position;
+
     /**
      * Calendar value.
      */
@@ -46,13 +50,23 @@ public final class CalendarCell extends AbstractStyleableCell {
      * @param calendar Calendar
      */
     public CalendarCell(final Calendar calendar) {
+        this(-1, calendar);
+    }
+
+    /**
+     * Ctor.
+     * @param column Cell position
+     * @param calendar Calendar
+     */
+    public CalendarCell(final int column, final Calendar calendar) {
         super();
+        this.position = column;
         this.value = calendar;
     }
 
     @Override
     public Cell attachTo(final Row row) {
-        final Cell cell = ECell.EMPTY.attachTo(row);
+        final Cell cell = new EmptyCell(this.position).attachTo(row);
         cell.setCellValue(this.value);
         return cell;
     }