Implementation code of java reflection tool class (Excel export)

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1. Define annotations, used to mark attributes used in the vo class

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
/**
 * @author fc
 * @date 2018-09-18
 */
@Target(value = {ElementType.FIELD})
@Retention(RetentionPolicy.RUNTIME)
public @interface Allow {
    String title() default "undefined";
}

2. Reflection tool class

import org.apache.poi.hssf.usermodel.HSSFWorkbook;
import org.apache.poi.ss.usermodel.Row;
import org.apache.poi.ss.usermodel.Sheet;
import org.apache.poi.ss.usermodel.Workbook;
import org.apache.poi.xssf.streaming.SXSSFWorkbook;
import org.apache.poi.xssf.usermodel.XSSFWorkbook;
import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.util.List;
/**
 * @author fc
 * @date 2018-09-18
 * @msg 反射工具类
 * @tips 字段必须使用@Allow注解 title属性定义标题
 */
public class ExcelCreateUtil {
    /**
     *
     * @param o object是vo类
     * @param suf 返回的excel文件后缀
     * @return
     * @throws Exception
     */
    public static Workbook createWorkBook(List<Object> o,ReturnSuf suf) throws Exception {
        //定义一个新的工作簿
        Workbook wb = suf.getValue().equals(ReturnSuf.XLSX.getValue())?new XSSFWorkbook():new HSSFWorkbook();
        //创建sheet
        Sheet sheet = wb.createSheet(String.valueOf(System.currentTimeMillis()));
        //创建行
        Row row = sheet.createRow(0);
        //第一行以注解@Allow title属性命名
        Class<?> aClass = o.get(0).getClass();
        Field[] fields1 = aClass.getDeclaredFields();
        int bj2 = 0;
        for (int j = 0; j < fields1.length; j++) {
            Allow annotation = fields1[j].getAnnotation(Allow.class);
            if (annotation != null) {
                fields1[j].setAccessible(true);
                row.createCell(bj2).setCellValue(annotation.title());
                bj2++;
            }
        }
        int bj1 = 1;
        for (int i = 0; i < o.size(); i++) {
            //获取当前对象
            Object o1 = o.get(i);
            //获取当前类类型
            Class<?> c = o.get(i).getClass();
            //获取当前类类型的所有属性
            Field[] fields = c.getDeclaredFields();
            //创建行-从第二行起
            Row row1 = sheet.createRow(bj1);
            bj1++;
            int bj = 0;
            for (int j = 0; j < fields.length; j++) {
                Allow annotation = fields1[j].getAnnotation(Allow.class);
                if (annotation != null) {
                    fields[j].setAccessible(true);
                    //得到属性名
                    String name = fields[j].getName();
                    //获取属性对应的get方法
                    Method method = c.getDeclaredMethod(toGet(name));
                    Object invoke = method.invoke(o1);
                    String value = invoke == null ? "" : invoke.toString();
                    //赋值
                    row1.createCell(bj).setCellValue(value);
                    bj++;
                }
            }
        }
        return wb;
    }
    //获取属性的set方法
    public static String toSet(String s) {
        final String SET = "set";
        if (Character.isUpperCase(s.charAt(0))) {
            return SET + s;
        } else {
            return SET + (new StringBuilder()).append(Character.toUpperCase(s.charAt(0))).append(s.substring(1)).toString();
        }
    }
    //获取属性的get方法
    public static String toGet(String s) {
        final String GET = "get";
        if (Character.isUpperCase(s.charAt(0))) {
            return GET + s;
        } else {
            return GET + (new StringBuilder()).append(Character.toUpperCase(s.charAt(0))).append(s.substring(1)).toString();
        }
    }
    public enum ReturnSuf {
        XLS(".xls后缀", ".xls"),
        /**
         *大数据量建议使用.xlsx
         */
        XLSX(".xlsx后缀", ".xlsx"),;
        private String key;
        private String value;
        ReturnSuf(String key, String value) {
            this.key = key;
            this.value = value;
        }
        public String getKey() {
            return key;
        }
        public void setKey(String key) {
            this.key = key;
        }
        public String getValue() {
            return value;
        }
        public void setValue(String value) {
            this.value = value;
        }
    }
}

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