java怎么将list写入excel

Java将List写入Excel：Apache POI库、数据建模、文件流处理、单元格格式化

如果你需要将Java中的List数据写入Excel文件，可以使用Apache POI库。Apache POI是一个功能强大的Java库，专门用于操作Microsoft Office文档，包括Excel文件。接下来，我将详细描述如何使用Apache POI将List写入Excel文件的步骤。

一、准备工作：添加Apache POI依赖

要使用Apache POI库，首先需要在项目中添加相应的依赖。如果你使用的是Maven项目，可以在pom.xml文件中添加以下依赖：

<dependency>
    <groupId>org.apache.poi</groupId>
    <artifactId>poi</artifactId>
    <version>5.0.0</version>
</dependency>
<dependency>
    <groupId>org.apache.poi</groupId>
    <artifactId>poi-ooxml</artifactId>
    <version>5.0.0</version>
</dependency>

如果你不是使用Maven项目，可以下载相应的jar包并手动添加到项目的类路径中。

二、创建Excel文件和工作表

首先，我们需要创建一个Excel文件和一个工作表。Apache POI提供了XSSFWorkbook和XSSFSheet类来完成这项工作：

import org.apache.poi.ss.usermodel.*;
import org.apache.poi.xssf.usermodel.XSSFWorkbook;
import java.io.FileOutputStream;
import java.io.IOException;
public class ExcelWriter {
    public static void main(String[] args) {
        Workbook workbook = new XSSFWorkbook();
        Sheet sheet = workbook.createSheet("Sheet1");
        try (FileOutputStream outputStream = new FileOutputStream("example.xlsx")) {
            workbook.write(outputStream);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

三、将List数据写入Excel

假设我们有一个包含用户信息的List，每个用户有姓名、年龄和电子邮件地址。我们需要将这些信息写入Excel文件中。

import org.apache.poi.ss.usermodel.*;
import org.apache.poi.xssf.usermodel.XSSFWorkbook;
import java.io.FileOutputStream;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
class User {
    String name;
    int age;
    String email;
    public User(String name, int age, String email) {
        this.name = name;
        this.age = age;
        this.email = email;
    }
}
public class ExcelWriter {
    public static void main(String[] args) {
        List<User> users = new ArrayList<>();
        users.add(new User("Alice", 30, "alice@example.com"));
        users.add(new User("Bob", 25, "bob@example.com"));
        users.add(new User("Charlie", 35, "charlie@example.com"));
        Workbook workbook = new XSSFWorkbook();
        Sheet sheet = workbook.createSheet("Sheet1");
        int rowCount = 0;
        // Create header row
        Row headerRow = sheet.createRow(rowCount++);
        headerRow.createCell(0).setCellValue("Name");
        headerRow.createCell(1).setCellValue("Age");
        headerRow.createCell(2).setCellValue("Email");
        for (User user : users) {
            Row row = sheet.createRow(rowCount++);
            row.createCell(0).setCellValue(user.name);
            row.createCell(1).setCellValue(user.age);
            row.createCell(2).setCellValue(user.email);
        }
        try (FileOutputStream outputStream = new FileOutputStream("example.xlsx")) {
            workbook.write(outputStream);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

四、处理单元格格式化

在许多情况下，简单地写入数据是不够的。我们可能还需要对单元格进行格式化，例如设置字体、颜色和对齐方式。Apache POI提供了丰富的API来实现这些功能。

设置字体和颜色

import org.apache.poi.ss.usermodel.*;
import org.apache.poi.xssf.usermodel.XSSFWorkbook;
import java.io.FileOutputStream;
import java.io.IOException;
public class ExcelWriter {
    public static void main(String[] args) {
        Workbook workbook = new XSSFWorkbook();
        Sheet sheet = workbook.createSheet("Sheet1");
        // Create a font
        Font headerFont = workbook.createFont();
        headerFont.setBold(true);
        headerFont.setFontHeightInPoints((short) 12);
        headerFont.setColor(IndexedColors.RED.getIndex());
        // Create a cell style
        CellStyle headerCellStyle = workbook.createCellStyle();
        headerCellStyle.setFont(headerFont);
        // Create header row
        Row headerRow = sheet.createRow(0);
        String[] columns = {"Name", "Age", "Email"};
        for (int i = 0; i < columns.length; i++) {
            Cell cell = headerRow.createCell(i);
            cell.setCellValue(columns[i]);
            cell.setCellStyle(headerCellStyle);
        }
        try (FileOutputStream outputStream = new FileOutputStream("example.xlsx")) {
            workbook.write(outputStream);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

设置列宽和自动换行

import org.apache.poi.ss.usermodel.*;
import org.apache.poi.xssf.usermodel.XSSFWorkbook;
import java.io.FileOutputStream;
import java.io.IOException;
public class ExcelWriter {
    public static void main(String[] args) {
        Workbook workbook = new XSSFWorkbook();
        Sheet sheet = workbook.createSheet("Sheet1");
        // Set column widths
        sheet.setColumnWidth(0, 5000);
        sheet.setColumnWidth(1, 3000);
        sheet.setColumnWidth(2, 7000);
        // Create a cell style for wrapping text
        CellStyle wrapTextStyle = workbook.createCellStyle();
        wrapTextStyle.setWrapText(true);
        // Create a sample row with wrapped text
        Row row = sheet.createRow(0);
        Cell cell = row.createCell(0);
        cell.setCellValue("This is a long text that should be wrapped in the cell.");
        cell.setCellStyle(wrapTextStyle);
        try (FileOutputStream outputStream = new FileOutputStream("example.xlsx")) {
            workbook.write(outputStream);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

五、处理日期和数字格式化

在实际应用中，处理日期和数字格式化是常见的需求。Apache POI提供了相关的API来处理这些格式化需求。

日期格式化

import org.apache.poi.ss.usermodel.*;
import org.apache.poi.xssf.usermodel.XSSFWorkbook;
import java.io.FileOutputStream;
import java.io.IOException;
import java.util.Date;
public class ExcelWriter {
    public static void main(String[] args) {
        Workbook workbook = new XSSFWorkbook();
        Sheet sheet = workbook.createSheet("Sheet1");
        CreationHelper createHelper = workbook.getCreationHelper();
        // Create a cell style for date formatting
        CellStyle dateCellStyle = workbook.createCellStyle();
        dateCellStyle.setDataFormat(createHelper.createDataFormat().getFormat("dd-MM-yyyy"));
        // Create a sample row with a date
        Row row = sheet.createRow(0);
        Cell cell = row.createCell(0);
        cell.setCellValue(new Date());
        cell.setCellStyle(dateCellStyle);
        try (FileOutputStream outputStream = new FileOutputStream("example.xlsx")) {
            workbook.write(outputStream);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

数字格式化

import org.apache.poi.ss.usermodel.*;
import org.apache.poi.xssf.usermodel.XSSFWorkbook;
import java.io.FileOutputStream;
import java.io.IOException;
public class ExcelWriter {
    public static void main(String[] args) {
        Workbook workbook = new XSSFWorkbook();
        Sheet sheet = workbook.createSheet("Sheet1");
        // Create a cell style for number formatting
        CellStyle numberCellStyle = workbook.createCellStyle();
        numberCellStyle.setDataFormat(workbook.createDataFormat().getFormat("#,##0.00"));
        // Create a sample row with a number
        Row row = sheet.createRow(0);
        Cell cell = row.createCell(0);
        cell.setCellValue(12345.678);
        cell.setCellStyle(numberCellStyle);
        try (FileOutputStream outputStream = new FileOutputStream("example.xlsx")) {
            workbook.write(outputStream);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

六、写入复杂数据结构

在实际应用中，我们可能需要写入更复杂的数据结构，例如包含多个子列表的对象。在这种情况下，我们可以递归地处理这些数据结构。

import org.apache.poi.ss.usermodel.*;
import org.apache.poi.xssf.usermodel.XSSFWorkbook;
import java.io.FileOutputStream;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
class Department {
    String name;
    List<Employee> employees;
    public Department(String name, List<Employee> employees) {
        this.name = name;
        this.employees = employees;
    }
}
class Employee {
    String name;
    int age;
    String email;
    public Employee(String name, int age, String email) {
        this.name = name;
        this.age = age;
        this.email = email;
    }
}
public class ExcelWriter {
    public static void main(String[] args) {
        List<Employee> employees1 = new ArrayList<>();
        employees1.add(new Employee("Alice", 30, "alice@example.com"));
        employees1.add(new Employee("Bob", 25, "bob@example.com"));
        List<Employee> employees2 = new ArrayList<>();
        employees2.add(new Employee("Charlie", 35, "charlie@example.com"));
        employees2.add(new Employee("David", 40, "david@example.com"));
        List<Department> departments = new ArrayList<>();
        departments.add(new Department("HR", employees1));
        departments.add(new Department("IT", employees2));
        Workbook workbook = new XSSFWorkbook();
        Sheet sheet = workbook.createSheet("Departments");
        int rowCount = 0;
        for (Department department : departments) {
            Row deptRow = sheet.createRow(rowCount++);
            deptRow.createCell(0).setCellValue(department.name);
            for (Employee employee : department.employees) {
                Row empRow = sheet.createRow(rowCount++);
                empRow.createCell(1).setCellValue(employee.name);
                empRow.createCell(2).setCellValue(employee.age);
                empRow.createCell(3).setCellValue(employee.email);
            }
        }
        try (FileOutputStream outputStream = new FileOutputStream("example.xlsx")) {
            workbook.write(outputStream);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

七、总结

通过以上步骤，我们可以使用Apache POI库将Java中的List数据写入Excel文件中。Apache POI提供了丰富的API，可以处理各种数据格式、单元格格式化和复杂的数据结构。无论是简单的数据写入还是复杂的格式化需求，Apache POI都能够满足我们的需求。希望这篇文章能够帮助你更好地理解和使用Apache POI库。