java常用BeanCompareUtil 注解 + 反射实现 (实例说明)

• • • 背景
    • 使用实例说明
    • 使用方式
    • 执行效果

在开发过程中经常会使用到一种场景就是比较内存中的两个bean 数据有什么同。其实这种功能算是一个非常常用的场景。

一共需要以下的几个模块

1. FieldComparison 自定义注解，主要是标识需要比较的bean 中的字段。
2. BeanCompareUtil 核心util 主要是实现compare 方法。
3. FieldMapping 字段映射关系，选用可以对特定的字段进行转义。
4. DefaultFieldMapping fieldMapping的实现类。可以扩展。

public class BeanCompareUtil {
    public static List compare(Object oldBean, Object newBean)
            throws InvocationTargetException, IllegalAccessException,
            IntrospectionException, NullPointerException, InstantiationException, NoSuchMethodException {
        if (oldBean == null || newBean == null) {
            throw new IllegalArgumentException("the argument must be not null");
        }
        if (oldBean.getClass() != newBean.getClass()) {
            return Collections.emptyList();
        }
        List list = new ArrayList<>();
        Class aClass = oldBean.getClass();
        while (aClass != null) {
            Field[] fieldList = aClass.getDeclaredFields();
            for (Field field : fieldList) {
                if (field.isAnnotationPresent(FieldComparison.class)) {
                    BeanCompareResult comResult = new BeanCompareResult();
                    PropertyDescriptor pd = new PropertyDescriptor(field.getName(), aClass);
                    String name = pd.getName();
                    comResult.setCode(name);
                    Method getMethod = pd.getReadMethod();
                    Object o1 = getMethod.invoke(oldBean);
                    Object o2 = getMethod.invoke(newBean);
                    if (o2 == null) {
                        continue;
                    }
                    String first = null == o1 ? "" : String.valueOf(o1).trim();
                    String second = String.valueOf(o2).trim();
                    if (field.isAnnotationPresent(FieldComparison.class)) {
                        FieldComparison fieldComparison = field.getAnnotation(FieldComparison.class);
                        String value = fieldComparison.codeName();
                        Class mapping = fieldComparison.mapping();
                        Method method = mapping.getMethod("mapping", Map.class);
                        Object invoke = method.invoke(mapping.newInstance(), new HashMap<>());
                        if (invoke != null) {
                            Map map = (Map) invoke;
                            String s = map.get(first);
                            String s2 = map.get(second);
                            comResult.setOldValue(s);
                            comResult.setNewValue(s2);
                        } else {
                            comResult.setOldValue(first);
                            comResult.setNewValue(second);
                        }
                        comResult.setName(value);
                    }
                    if (!first.equals(second)) {
                        list.add(comResult);
                    }
                }
            }
            aClass = aClass.getSuperclass();
        }
        return list;
    }
}

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.FIELD)
public @interface FieldComparison {

    
    String codeName() default "";

    
    Class mapping() default DefaultFieldMapping.class;
}

public interface FieldMapping {
    Map mapping(Map map);
}

public class DefaultFieldMapping implements FieldMapping {
    @Override
    public Map mapping(Map map) {
        return null;
    }
}

1. 在需要compare 的地方加上注释
   
2. 定义结果接受的bean

public class BeanCompareResult {
    private String code;
    private String name;
    private String oldValue;
    private String newValue;

    private String extendRemark;

    public String getExtendRemark() {
        return extendRemark;
    }

    public void setExtendRemark(String extendRemark) {
        this.extendRemark = extendRemark;
    }

    public String getCode() {
        return code;
    }

    public void setCode(String code) {
        this.code = code;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getOldValue() {
        return oldValue;
    }

    public void setOldValue(String oldValue) {
        this.oldValue = oldValue;
    }

    public String getNewValue() {
        return newValue;
    }

    public void setNewValue(String newValue) {
        this.newValue = newValue;
    }

    @Override
    public String toString() {
        return "BeanCompareResult{" +
                "code='" + code + ''' +
                ", name='" + name + ''' +
                ", oldValue='" + oldValue + ''' +
                ", newValue='" + newValue + ''' +
                ", extendRemark='" + extendRemark + ''' +
                '}';
    }
}

3. 传入oldbean 和 newbean进行比较和接收结果。