在Vaadin中通过PostgreSQL下载CSV

Button downloadButton = new Button("Download CSV");
downloadButton.addClickListener(event -> {
    try {
        // 执行查询语句，获取需要导出为CSV的数据
        Connection connection = DriverManager.getConnection("jdbc:postgresql://localhost:5432/mydatabase", "username", "password");
        Statement statement = connection.createStatement();
        ResultSet resultSet = statement.executeQuery("SELECT * FROM mytable");

        // 将查询结果转换为CSV格式的字符串
        StringBuilder csvData = new StringBuilder();
        ResultSetMetaData metaData = resultSet.getMetaData();
        int columnCount = metaData.getColumnCount();
        for (int i = 1; i <= columnCount; i++) {
            csvData.append(metaData.getColumnName(i));
            if (i < columnCount) {
                csvData.append(",");
            }
        }
        csvData.append("\n");
        while (resultSet.next()) {
            for (int i = 1; i <= columnCount; i++) {
                csvData.append(resultSet.getString(i));
                if (i < columnCount) {
                    csvData.append(",");
                }
            }
            csvData.append("\n");
        }

        // 创建临时文件，将CSV字符串写入该文件
        File tempFile = File.createTempFile("data", ".csv");
        FileWriter fileWriter = new FileWriter(tempFile);
        fileWriter.write(csvData.toString());
        fileWriter.close();

        // 使用Vaadin的FileDownloader组件提供临时文件进行下载
        FileDownloader fileDownloader = new FileDownloader(new FileResource(tempFile));
        fileDownloader.extend(downloadButton);
    } catch (SQLException | IOException e) {
        e.printStackTrace();
    }
});

// 将按钮添加到UI中
add(downloadButton);