一个导出数据的功能模块的优化过程

业务场景：从学生数据库导出一张表为Excel

  1. Excel导出工具类

    /**
 * @author Cao Jiwen
 * @version V1.0
 */
public class ExcelExportUtil {
    /**
     * @param outputStream 输出流
     * @param columnList 列名列表
     * @param dataList 数据列表
     */
    public static void export(OutputStream outputStream, List<String> columnList,List<List<String>> dataList) throws IOException {
        //excel文件主题对象
        SXSSFWorkbook wb = null;
        try{
            //内存的最大行数，防止内存溢出
            wb = new SXSSFWorkbook(1000);
            //创建一个sheet
            SXSSFSheet sheet1 = wb.createSheet("数据");
            //行索引
            int excelRow = 0;
            //创建第一行，列名行
            Row titleRow = sheet1.createRow(excelRow++);
            if (ObjectUtil.isNotEmpty(columnList)){
                //遍历列名表
                for (int i = 0; i < columnList.size(); i++) {
                    //创建一个单元格
                    Cell cell = titleRow.createCell(i);
                    //设置单元格的值
                    cell.setCellValue(columnList.get(i));
                }
            }
            if (ObjectUtil.isNotEmpty(dataList)){
                for (int i = 0; i < dataList.size(); i++) {
                    //创建数据行
                    Row dataRow = sheet1.createRow(excelRow++);
                    //遍历出单个数据
                    for (int j = 0; j < dataList.get(0).size(); j++) {
                        Cell cell = dataRow.createCell(j);
                        cell.setCellValue(dataList.get(i).get(j));
                    }
                }
            }
            wb.write(outputStream);
        }catch (Exception e){
            e.printStackTrace();
            throw e;
        }finally {
            if (wb != null){
                wb.close();
            }
            if (outputStream != null){
                outputStream.close();
            }
        }
    }
}

  2. 导出过程

    public static void main(String[] args) throws IOException {
    //调用方角度
    //查询数据
    Student student1 = new Student("luoxi", 18);
    Student student2 = new Student("jixian", 19);
    //创建输出流
    FileOutputStream fileOutputStream = new FileOutputStream("D:\\Javaproject\\ myApp\\exportItem\\src\\main\\java\\学生信息表.xlsx");
    //创建列名列表
    List<String> columList = new ArrayList<>();
    columList.add("姓名");
    columList.add("年龄");
    //创建数据列表
    List<List<String>> dataList = new ArrayList<>();
    //创建单条数据列表
    List<String> data1 = new ArrayList<>();
    List<String> data2 = new ArrayList<>();
    data1.add(student1.getName());
    data1.add(student1.getAge().toString());
    data2.add(student2.getName());
    data2.add(student2.getAge().toString());
    dataList.add(data1);
    dataList.add(data2);
    ExcelExportUtil.export(fileOutputStream,columList,dataList);
}

  3. 使用反馈

    最直接的感受就是，被调用方每次都需要一次一次的创建列表，再从对象中提取数据，非常麻烦

  4. 代码改进

    第一步：反射改进

    不传列表，那就直接传对象，那就要从对象中自己提取数据，对象我事先不知道的，所以要用到反射

    /**
 * @param outputStream 输出流
 * @param columList 列名列表
 * @param dataList 数据列表
 */
public static void reflectExport(OutputStream outputStream,List<String> columList,List dataList) throws IllegalAccessException, IOException {
    //健壮性检验
    if (ObjectUtil.isEmpty(dataList)){
        return;
    }
    List<List<String>> allList = new ArrayList<>();
    //获取class文件
    Class<?> aClass = dataList.get(0).getClass();
    //通过class文件获取对象属性
    Field[] declaredFields = aClass.getDeclaredFields();
    for (int i = 0; i < dataList.size(); i++) {
        List<String> list = new ArrayList<>();
        for (int j = 0; j < declaredFields.length; j++) {
            //由于属性是private修饰，将可见性设为true
            Field declareField = declaredFields[j];
            declareField.setAccessible(true);
            Object o = declareField.get(dataList.get(i));
            if (o != null){
                list.add(o.toString());
            }
        }
        allList.add(list);
    }
    export(outputStream,columList,allList);
}

    继续优化：如果不想导出对象的全部数据呢

    第二步：注解改进

    • 不想导出全部属性，可以通过给属性标记
    • 将导出的属性排序，通过注解上的信息，标记属性的顺序
    //在运行时生效
@Retention(RetentionPolicy.RUNTIME)
//目标注解，标识属性
@Target(ElementType.FIELD)
public @interface Excel {
    int order();
}

    public class Student {
    private String id;
    @Excel(order = 1)
    private String name;
    @Excel(order = 2)
    private Integer age;
}

    public static void reflectExport(OutputStream outputStream,List<String> columList,List dataList) throws IllegalAccessException, IOException {
    //健壮性检验
    if (ObjectUtil.isEmpty(dataList)){
        return;
    }
    List<List<String>> allList = new ArrayList<>();
    //获取class文件
    Class<?> aClass = dataList.get(0).getClass();
    //通过class文件获取对象属性
    Field[] declaredFields = aClass.getDeclaredFields();
    //排除没有被标记的属性
    List<Field> fields = Arrays.asList(declaredFields).stream().filter(field -> field.isAnnotationPresent(Excel.class)).collect(Collectors.toList());
    //属性排序
    fields = fields.stream().sorted(Comparator.comparingInt(field -> field.getAnnotation(Excel.class).order())).collect(Collectors.toList());

    for (int i = 0; i < dataList.size(); i++) {
        List<String> list = new ArrayList<>();
        for (int j = 0; j < fields.size(); j++) {
            Field declareField = fields.get(j);
            declareField.setAccessible(true);
            Object o = declareField.get(dataList.get(i));
            if (o != null){
                list.add(o.toString());
            }
        }
        allList.add(list);
    }
    export(outputStream,columList,allList);
}