前段时间，领导分配一个统计销售区域汇总的数据，解决方案使用到了反射获取注解，通过注解获取属性或者设置字段属性。
问题描述
查询公司列表，分别是公司id、区域id、区域名称:
| 公司id | 区域id | 区域名称 |
|---|---|---|
| 1 | 1 | 华南 |
| 2 | 2 | 华北 |
| 3 | 2 | 华北 |
| 4 | 3 | 华东 |
| 5 | 3 | 华东 |
创建公司类Company：
public class Company {
public Company(Integer id, Integer areaId, String areaName) {
this.id = id;
this.areaId = areaId;
this.areaName = areaName;
}
private Integer id;
private Integer areaId;
private String areaName;
// 省略get/set方法
}
最终解决
要求汇总各个区域公司数量,得到如下汇总：
| 区域id | 区域名称 | 公司总数 |
|---|---|---|
| 1 | 华南 | 1 |
| 2 | 华北 | 2 |
| 3 | 华东 | 2 |
最终区域实体AreaStatistic:
public class AreaStatistic {
@ColumnProperty("华东大区")
private Integer eastChina = 0;
@ColumnProperty("华东id")
private Integer eastChinaId;
@ColumnProperty("华南大区")
private Integer southChina = 0;
@ColumnProperty("华南id")
private Integer southChinaId;
@ColumnProperty("华北大区")
private Integer northChina = 0;
@ColumnProperty("华北id")
private Integer northChinaId;
@Override
public String toString() {
return "AreaStatistic{\n" +
"华东Id=" + eastChinaId +
",华东=" + eastChina +
", \n华南Id=" + southChinaId +
", 华南=" + southChina +
", \n华北Id=" + northChinaId +
", 华北=" + northChina +
'}';
}
// 省略get/set方法
}
if/else 普通解法
AreaStatistic areaStatistic = new AreaStatistic();
for (Company company:companyList) {
String areaName = company.getAreaName();
if ("华南".equals(areaName)) {
areaStatistic.setSouthChina(areaStatistic.getSouthChina()+1);
areaStatistic.setSouthChinaId(company.getAreaId());
} else if ("华北".equals(areaName)) {
areaStatistic.setNorthChina(areaStatistic.getNorthChina()+1);
areaStatistic.setNorthChinaId(company.getAreaId());
} else if ("华东".equals(areaName)) {
areaStatistic.setEastChina(areaStatistic.getEastChina()+1);
areaStatistic.setEastChinaId(company.getAreaId());
}
}
输出：
华东Id=3,华东=2,
华南Id=1, 华南=1,
华北Id=2, 华北=2
这种做法的缺点：
- 要写大量的条件判断语句，非常的繁琐。
- 增加和减少统计区域，都要修改代码。
针对上面的缺点，使用反射获取注解，通过注解获取属性赋值。
通过反射注解赋值属性
解题思路
1.遍历公司列表，获取到区域id和区域名称。
2.创建自定义注解@ColumnProperty:
@Target({ElementType.METHOD, ElementType.FIELD})
@Retention(RetentionPolicy.RUNTIME)
public @interface ColumnProperty {
String value() default "";
}
3.通过反射获取属性，然后遍历字段属性获取注解。
在AreaStatistic字段属性上添加注解：
@ColumnProperty("华东大区")
private Integer eastChina = 0;
@ColumnProperty("华东id")
private Integer eastChinaId;
@ColumnProperty("华南大区")
private Integer southChina = 0;
@ColumnProperty("华南id")
private Integer southChinaId;
@ColumnProperty("华北大区")
private Integer northChina = 0;
@ColumnProperty("华北id")
private Integer northChinaId;
4.通过反射获取属性，然后遍历字段属性获取注解。
Class staticClass = areaStatistic.getClass();
Field[] fields = staticClass.getDeclaredFields();
for (Field field : fields) {
ColumnProperty property = field.getAnnotation(ColumnProperty.class);
String value = property.value();
}
5.匹配区域名称和字段属性，比如遍历公司区域是华东，就遍历到华东大区注解对应的字段，并赋值或者获取字段值。
if (value != null) {
int indexOf = value.indexOf("大区");
if (indexOf != -1 && value.length() == 4) {
if (areaName.equals(value.substring(0,2))) {
field.setAccessible(true);
field.set(areaStatistic,(Integer) field.get(areaStatistic) + 1);
}
}
}
6.区域id赋值也是相同的解题思路。
根据上面的思路，有如下代码汇总：
// 遍历公司
for (Company company:companyList) {
setAreaProperty(areaStatistic2,company.getAreaName(),company.getAreaId());
}
private void setAreaProperty(AreaStatistic areaStatistic,String areaName,Integer areaId) throws IllegalAccessException {
// 反射获取注解
Class staticClass = areaStatistic.getClass();
Field[] fields = staticClass.getDeclaredFields();
for (Field field : fields) {
ColumnProperty property = field.getAnnotation(ColumnProperty.class);
String value = property.value();
if (value != null) {
int indexOf = value.indexOf("大区");
if (indexOf != -1 && value.length() == 4) {
// 匹配到注解属性并赋值
if (areaName.equals(value.substring(0,2))) {
field.setAccessible(true);
field.set(areaStatistic,(Integer) field.get(areaStatistic) + 1);
for (Field idField : fields) {
ColumnProperty idProperty = idField.getAnnotation(ColumnProperty.class);
String idValue = idProperty.value();
if (idValue.equals(areaName+"id")) {
idField.setAccessible(true);
idField.set(areaStatistic,areaId);
break;
}
}
break;
}
}
}
}
}
输出：
华东Id=3,华东=2,
华南Id=1, 华南=1,
华北Id=2, 华北=2
汇总某些字段的和
上面算出各个区域的汇总之后，还要算出全部区域的总和，这里还是使用到注解，把属性字段包含大区都累加起来:
AreaStatistic statistic = new AreaStatistic();
statistic.setEastChina(2);
statistic.setNorthChina(3);
statistic.setSouthChina(1);
int sum = 0;
Class staticClass = statistic.getClass();
Field[] fields = staticClass.getDeclaredFields();
for (Field field : fields) {
ColumnProperty property = field.getAnnotation(ColumnProperty.class);
String value = property.value();
if (value.indexOf("大区") != -1) {
field.setAccessible(true);
sum += field.get(statistic) == null ? 0 : (Integer) field.get(statistic);
}
}
System.out.println(sum);
输出结果：
6
总结
1.自定义注解，通过反射获取注解
2.通过匹配注解值，获取或者复制对应的字段属性。
赋值主要代码为:
field.setAccessible(true);
field.set(Model,value);源码
package reflect;
import org.junit.Test;
import reflect.annotation.ColumnProperty;
import reflect.model.AreaStatistic;
import reflect.model.Company;
import javax.print.DocFlavor;
import java.lang.reflect.Field;
import java.util.ArrayList;
import java.util.List;
public class SetValueByAnnotation {
@Test
public void test() throws IllegalAccessException {
// 添加数据
Company company5 = new Company(1,1,"华南");
Company company1 = new Company(2,2,"华北");
Company company2 = new Company(3,2,"华北");
Company company3 = new Company(4,3,"华东");
Company company4 = new Company(5,3,"华东");
List<Company> companyList = new ArrayList<>();
companyList.add(company5);
companyList.add(company1);
companyList.add(company2);
companyList.add(company3);
companyList.add(company4);
// 解法1
AreaStatistic areaStatistic = new AreaStatistic();
for (Company company:companyList) {
String areaName = company.getAreaName();
if ("华南".equals(areaName)) {
areaStatistic.setSouthChina(areaStatistic.getSouthChina()+1);
areaStatistic.setSouthChinaId(company.getAreaId());
} else if ("华北".equals(areaName)) {
areaStatistic.setNorthChina(areaStatistic.getNorthChina()+1);
areaStatistic.setNorthChinaId(company.getAreaId());
} else if ("华东".equals(areaName)) {
areaStatistic.setEastChina(areaStatistic.getEastChina()+1);
areaStatistic.setEastChinaId(company.getAreaId());
}
}
System.out.println(areaStatistic);
// 解法二
AreaStatistic areaStatistic2 = new AreaStatistic();
for (Company company:companyList) {
setAreaProperty(areaStatistic2,company.getAreaName(),company.getAreaId());
}
System.out.println(areaStatistic2);
}
private void setAreaProperty(AreaStatistic areaStatistic,String areaName,Integer areaId) throws IllegalAccessException {
Class staticClass = areaStatistic.getClass();
Field[] fields = staticClass.getDeclaredFields();
for (Field field : fields) {
ColumnProperty property = field.getAnnotation(ColumnProperty.class);
String value = property.value();
if (value != null) {
int indexOf = value.indexOf("大区");
if (indexOf != -1 && value.length() == 4) {
if (areaName.equals(value.substring(0,2))) {
field.setAccessible(true);
field.set(areaStatistic,(Integer) field.get(areaStatistic) + 1);
for (Field idField : fields) {
ColumnProperty idProperty = idField.getAnnotation(ColumnProperty.class);
String idValue = idProperty.value();
if (idValue.equals(areaName+"id")) {
idField.setAccessible(true);
idField.set(areaStatistic,areaId);
break;
}
}
break;
}
}
}
}
}
@Test
public void accumulate() throws IllegalAccessException {
AreaStatistic statistic = new AreaStatistic();
statistic.setEastChina(2);
statistic.setNorthChina(3);
statistic.setSouthChina(1);
int sum = 0;
Class staticClass = statistic.getClass();
Field[] fields = staticClass.getDeclaredFields();
for (Field field : fields) {
ColumnProperty property = field.getAnnotation(ColumnProperty.class);
String value = property.value();
if (value.indexOf("大区") != -1) {
field.setAccessible(true);
sum += field.get(statistic) == null ? 0 : (Integer) field.get(statistic);
}
}
System.out.println(sum);
}
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