Using Apache POI2 for Excel processing in Java API development

With the rapid development of modern technology, data processing has become an indispensable part of modern society. Especially in businesses, Excel files are widely used tools to record and analyze data. However, manually editing and processing large Excel files can often be time-consuming and error-prone. Therefore, using Java API to process Excel files is a more efficient and reliable solution. Apache POI2, as a popular Java API, provides support for reading and writing Microsoft Office files and is the preferred Excel file processing tool for Java developers.

This article will discuss the basic usage of Apache POI2 and some common operations for processing Excel files.

What is Apache POI2

Apache POI2 is a set of Java APIs provided by the Apache organization for processing Microsoft Office files. It supports reading and writing operations on Excel, Word and PowerPoint files. The purpose of Apache POI2 is to provide a simple and easy-to-use interface that enables programmers to read and write Microsoft Office files without knowing the details of the file format.

The main functions of Apache POI2 include:

• Reading and writing Excel, Word and PowerPoint files;
• Processing cells, rows, and columns of Excel files and workbooks;
• Supports data types such as dates, numbers, and strings in Excel files;
• Supports formulas, images, charts, etc. in Excel files.

Install and configure Apache POI2

Before using Apache POI2, you need to install and configure it. The latest version of Apache POI2 can be downloaded from the official website. Once downloaded, simply add the Apache POI2 jar file to your project's classpath to get started.

Basic usage

In Apache POI2, Excel files are represented as a workbook (Workbook), and each workbook contains multiple worksheets (Sheets). Each worksheet contains multiple cells (Cell), and each cell can contain a data type, such as a number, a string, or a date.

First, before using Apache POI2, you need to introduce the relevant packages:

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import org.apache.poi.hssf.usermodel.HSSFWorkbook;
import org.apache.poi.ss.usermodel.*;

Next, create a new workbook:

Workbook workbook = new HSSFWorkbook();  // 创建一个新的 Excel 工作簿
Sheet sheet = workbook.createSheet("Sheet1");  // 创建一个新的工作表
Row row = sheet.createRow(0);  // 创建第一行
Cell cell = row.createCell(0);  // 创建第一个单元格
cell.setCellValue("Hello World");  // 设置单元格的值

In the above code, We create a new workbook, sheet, rows, and cells and set the string "Hello World" as the value of the first cell. The HSSFWorkbook class is used here to create a new Excel workbook. For Excel 2007 and above, you can use the XSSFWorkbook class.

Next, write the workbook to a file:

FileOutputStream outputStream = new FileOutputStream("example.xls");
workbook.write(outputStream);
workbook.close();

In the above code, we write the workbook to a file named "example.xls" and Close the workbook when finished.

Now, we have created a simple Excel file. Next, we'll discuss how to read and modify existing Excel files.

Reading Excel Files

In Apache POI2, an Excel file can be read in different ways. The most common method is to use the FileInputStream class to read a file into memory.

FileInputStream inputStream = new FileInputStream(new File("example.xls"));
Workbook workbook = new HSSFWorkbook(inputStream);  // 创建一个新的工作簿对象
Sheet sheet = workbook.getSheetAt(0);  // 获取第一个工作表
Row row = sheet.getRow(0);  // 获取第一行
Cell cell = row.getCell(0);  // 获取第一个单元格
String value = cell.getStringCellValue();  // 获取单元格的值

In the above code, we use the FileInputStream class to read the Excel file into memory and use the HSSFWorkbook class to convert it into a workbook object. Next, we get the first sheet, first row and first cell, and in the last row we get the string value in the cell.

Modify Excel files

In addition to setting the value of a cell when creating it, we can also use Apache POI2 to modify existing cells.

FileInputStream inputStream = new FileInputStream(new File("example.xls"));
Workbook workbook = new HSSFWorkbook(inputStream);  // 创建一个新的工作簿对象
Sheet sheet = workbook.getSheetAt(0);  // 获取第一个工作表
Row row = sheet.getRow(0);  // 获取第一行
Cell cell = row.getCell(0);
cell.setCellValue("New Value");  // 设置单元格的新值
FileOutputStream outputStream = new FileOutputStream("example.xls");
workbook.write(outputStream);  // 将修改后的工作簿写入文件
workbook.close();

In the above code, we use the FileInputStream and HSSFWorkbook classes to create a workbook object and read out the first worksheet, first row and first cell. Next, use the setCellValue() method to set the cell's value to "New Value". Finally, use the FileOutputStream and Workbook classes to write the modified workbook to a file.

Summary

Apache POI2 is a powerful Java API that provides rich functions to read, write and operate Excel files. This article introduces the basic usage of Apache POI2 and common Excel file processing operations. In fact, Apache POI2 can perform more advanced operations, such as merging and splitting cells, drawing charts, formatting cells, and more. Using Apache POI2, Java developers can easily read, write, and process Excel files, increasing productivity and reducing manual errors.

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