EasyExcel

EasyExcel is a Java toolkit designed for parsing and generating Excel files with extremely low memory consumption. Unlike Apache POI, which can consume significant memory (e.g., 100MB for a 3MB file) because it often performs unzipping and storage in memory, EasyExcel rewrites the parsing logic to be highly memory-efficient.

Performance Benchmark (v3.0.2+): A machine with only 64MB RAM can read a 75MB Excel file (460,000 rows, 25 columns) in approximately 20 seconds.

EasyExcel is transitioning into a maintenance mode.

• What this means: The team will ensure basic functionality remains stable and will provide bug fixes, but there will be no new features actively added.
• Recommendation: Users are encouraged to evaluate and potentially migrate to other products for new feature requirements.

EasyExcel is a Java framework designed for high-performance Excel parsing and generation. Unlike Apache POI, which can be very memory-intensive (e.g., using ~100MB of memory for a 3MB Excel file via SAX), EasyExcel re-implements the parsing of Excel 07 files to significantly reduce memory consumption (e.g., reducing usage to just a few MBs).

Key features:

• Low Memory Footprint: Designed to prevent OutOfMemoryError even with very large files.
• High Speed: Supports a 'Speed Mode' (极速模式) for even faster processing, though it uses slightly more memory (~100MB+).
• Simplified API: Provides a high-level model conversion wrapper for Excel 03 files, making them easier to use than standard POI SAX modes.

When processing Excel 07+ files, the 'Shared Strings' concept can cause memory usage to balloon to 3-10x the file size. EasyExcel manages this by switching between in-memory storage and file-based storage for shared strings to prevent OutOfMemoryError.

Default Behavior

• Shared Strings < 5MB: Stored in memory (occupies ~15-50MB RAM).
• Shared Strings > 5MB: Stored in temporary files. A default of 20MB of RAM is used to cache these strings to balance speed and memory.
• Estimated Memory: For a very large file, expect a permanent memory footprint of approximately 30MB.

Note: Using file-based storage may reduce reading efficiency by 30-50% due to disk I/O.

Version Support

• EasyExcel 2+: Works on Java 6 or Java 7.
• EasyExcel 3+: Works on Java 8 or higher.

Upgrading from 2.x to 3.x

Upgrading across major versions is not recommended due to incompatibilities:

• Interceptors: Custom interceptors used to modify styles may cause issues even if they compile.
• Exception Handling: During reading, the invoke function may throw exceptions directly without being wrapped in an ExcelAnalysisException.
• Annotations: Style and other annotations involving boolean or enumerations have changed (new default values added). You may need to update these annotations to resolve compiler errors.

Starting from version 3.3.0, EasyExcel provides enhanced CSV support:

• BOM Support: When writing CSV files, EasyExcel now includes BOM (Byte Order Mark) data by default to prevent encoding issues (garbled text) when opening files in Microsoft Office.
• Encoding: You can set specific read/write encodings for CSV files.
• Auto-detection: If parsing via a file stream, EasyExcel will now default to identifying the format as CSV if it cannot determine otherwise, rather than throwing an exception.

EasyExcel uses a hierarchical configuration model where settings applied to a Workbook are inherited by its Sheets.

• EasyExcel: The entry point class used to initiate all operations.
• Workbook (ReadWorkbook/WriteWorkbook): Represents the entire Excel file. You should build one per Excel file.
• Sheet (ReadSheet/WriteSheet): Represents a single page within the Excel file. You must build one for every sheet you wish to process.
• ReadListener: A callback mechanism triggered after every row is read to process data.
• WriteHandler: A callback mechanism triggered during various writing stages (e.g., creating cells or tables).

Configuration Scope Rule: Settings applied via EasyExcel...sheet() are scoped to that specific sheet. Settings applied before the .sheet() method call apply to the entire Workbook.

To format code according to project standards in Eclipse, import the provided Eclipse configuration file:

1. Navigate to Window -> Preferences -> Java -> Code Style -> Formatter.
2. Click Import.
3. Select the file style/eclipse/codestyle.xml from the repository.
4. In the Active profile section, ensure P3C-CodeStyle is selected.
5. Click Apply to complete the configuration.

File: style/eclipse/codestyle.xml

To perform a simple write operation:

1. Create an entity class (e.g., DemoData) representing the data to be written.
2. Call EasyExcel.write() specifying the file path and the entity class.
3. Use .sheet("sheetName") to define the sheet and .doWrite(data) to write the data. The file stream will be closed automatically. If you need to write in the older Excel 03 format, pass the excelType parameter.

@Test
public void simpleWrite() {
    String fileName=TestFileUtil.getPath()+"write"+System.currentTimeMillis()+".xlsx";
    // Specify the file name, the entity class, the sheet name, and the data to write
    EasyExcel.write(fileName,DemoData.class).sheet("模板").doWrite(data());
}

To use EasyExcel in your Java project, add the following dependency to your pom.xml. Note that version 3+ requires Java 8 or higher.

<dependency>
    <groupId>com.alibaba</groupId>
    <artifactId>easyexcel</artifactId>
    <version>3.0.2</version>
</dependency>