Cell Merging

This chapter introduces cell merging strategies when writing Excel files.

Overview

When generating Excel reports, you may need to merge cells — for example, merging repeated category names in a column, or creating summary rows. Fesod supports two approaches: annotation-based and strategy-based merging.

Annotation-Based Merging

Overview

Annotate a field with @ContentLoopMerge(eachRow = N) to automatically merge every N rows in that column.

POJO Class

@Getter
@Setter
@EqualsAndHashCode
public class DemoMergeData {
    @ContentLoopMerge(eachRow = 2)
    @ExcelProperty("String Title")
    private String string;

    @ExcelProperty("Date Title")
    private Date date;

    @ExcelProperty("Number Title")
    private Double doubleData;
}

Code Example

@Test
public void annotationMergeWrite() {
    String fileName = "annotationMergeWrite" + System.currentTimeMillis() + ".xlsx";
    FesodSheet.write(fileName, DemoMergeData.class)
        .sheet()
        .doWrite(data());
}

Result

| String Title | Date Title          | Number Title |
|--------------|---------------------|--------------|
| String0      | 2025-01-01 00:00:00 | 0.56         |
| (merged)     | 2025-01-01 00:00:00 | 0.56         |
| String1      | 2025-01-01 00:00:00 | 0.56         |
| (merged)     | 2025-01-01 00:00:00 | 0.56         |

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Strategy-Based Merging

Overview

Register a LoopMergeStrategy(eachRow, columnIndex) as a write handler. More flexible — can be configured at runtime and applied to any column.

Code Example

@Test
public void strategyMergeWrite() {
    String fileName = "strategyMergeWrite" + System.currentTimeMillis() + ".xlsx";

    // Merge every 2 rows in column 0
    LoopMergeStrategy strategy = new LoopMergeStrategy(2, 0);
    FesodSheet.write(fileName, DemoData.class)
        .registerWriteHandler(strategy)
        .sheet()
        .doWrite(data());
}

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Custom Merge Strategy

Overview

For complex merging logic (e.g., merge based on data content), implement the AbstractMergeStrategy class.

Code Example

public class CustomMergeStrategy extends AbstractMergeStrategy {
    @Override
    protected void merge(Sheet sheet, Cell cell, Head head, Integer relativeRowIndex) {
        if (relativeRowIndex != null && relativeRowIndex % 2 == 0 && head.getColumnIndex() == 0) {
            // Note: +1 assumes a single header row. For multi-row headers, use cell.getRowIndex() instead.
            int startRow = relativeRowIndex + 1;
            int endRow = startRow + 1;
            sheet.addMergedRegion(new CellRangeAddress(startRow, endRow, 0, 0));
        }
    }
}

Usage:

@Test
public void customMergeWrite() {
    String fileName = "customMergeWrite" + System.currentTimeMillis() + ".xlsx";
    FesodSheet.write(fileName, DemoData.class)
        .registerWriteHandler(new CustomMergeStrategy())
        .sheet()
        .doWrite(data());
}

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When to Use Which

Approach	Best For
@ContentLoopMerge	Simple, fixed merge patterns baked into the data class
LoopMergeStrategy	Dynamic merging, runtime configuration
AbstractMergeStrategy	Complex merging based on data content or custom rules