Java通过反射注解赋值的方法详解

2024-04-02 19:04:59 280人浏览薄情痞子

Python 官方文档：入门教程 => 点击学习

摘要

目录问题描述最终解决if/else 普通解法通过反射注解赋值属性解题思路汇总某些字段的和总结源码前段时间，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

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);
    }

}

到此这篇关于Java通过反射注解赋值的方法详解的文章就介绍到这了,更多相关Java反射注解赋值内容请搜索编程网以前的文章或继续浏览下面的相关文章希望大家以后多多支持编程网！

您可能感兴趣的文档:

--结束END--

本文标题: Java通过反射注解赋值的方法详解

本文链接: https://lsjlt.com/news/164936.html(转载时请注明来源链接)

有问题或投稿请发送至: 邮箱/279061341@qq.com QQ/279061341