java 自定义注解实现不同对象之间的拷贝（支持大小写、驼峰转换）

要实现两个属性名称完全不同的对象之间的拷贝。具体如下

• 原对象

  @Data
  public class Source {
  
      
      @PropertyTransform(name = "targetName",transformStrategy = TransformStrategy.DEFAULT)
      String sourceName;
  
      
      @PropertyTransform(transformStrategy = TransformStrategy.LOWER)
      String LOWER;
  
      
      @PropertyTransform(transformStrategy = TransformStrategy.UPPER)
      String upper;
  
      
      @PropertyTransform(transformStrategy = TransformStrategy.HUMP)
      String high_and_down;
  
  }
  

• 目标对象

@Data
public class Target {

    String targetName;

    String lower;

    String UPPER;

    String highAndDown;

}

我们可以看到上面原对象上的属性加入了自定义注解==@PropertyTransform==，具体实现如下

• 自定义注解

//RetentionPolicy.RUNTIME：注解不仅被保存到class文件中，jvm加载class文件之后，仍然存在；
@Retention(RetentionPolicy.RUNTIME)
//声明注解的作用域在属性上
@Target(ElementType.FIELD)
@Component
public @interface PropertyTransform {

    
    @AliasFor("name")
    String value() default "";

    
    @AliasFor("value")
    String name() default "";

    
    TransformStrategy transformStrategy() default TransformStrategy.DEFAULT;

}

• 转换策略枚举类

  public enum TransformStrategy {
  
      
      DEFAULT,
  
      
      LOWER,
  
      
      UPPER,
  
      
      HUMP,
  
  }
  

• 编写转换工具类，利用反射实现需求

public class PropertiesTransformUtils {

    private static final Pattern linePattern = Pattern.compile("_(\w)");

    @SneakyThrows
    public static Object copy(Object source,Class target){

        Class sourceClass = source.getClass();

        //获取原实体下的所有属性
        Field[] fields = sourceClass.getDeclaredFields();

        //记录转换名称后的属性名以及属性值
        Map objMap = new HashMap<>(fields.length);

        for (Field field : fields) {
            field.setAccessible(true);
            //获取属性上的注解
            PropertyTransform propertyTransform = field.getAnnotation(PropertyTransform.class);
            //根据不同的策略进行对原实体的属性名称进行修改
            if (propertyTransform != null){
                if (!"".equals(propertyTransform.name())){
                    objMap.put(propertyTransform.name(),field.get(source));
                }else if (!TransformStrategy.DEFAULT.equals(propertyTransform.transformStrategy())){
                    if (TransformStrategy.LOWER.equals(propertyTransform.transformStrategy())){
                        objMap.put(field.getName().toLowerCase(),field.get(source));
                    }else
                    if (TransformStrategy.UPPER.equals(propertyTransform.transformStrategy())){
                        objMap.put(field.getName().toUpperCase(),field.get(source));
                    }else
                    if (TransformStrategy.HUMP.equals(propertyTransform.transformStrategy())){
                        objMap.put(lineToHump(field.getName()),field.get(source));
                    }
                }
            }
        }
		
        //将值拷贝到目标实体
        Object targetObj = target.newInstance();
        for (Field declaredField : target.getDeclaredFields()) {
            Object value = objMap.getOrDefault(declaredField.getName(),null);
            declaredField.setAccessible(true);
            declaredField.set(targetObj,value);
        }

        return targetObj;
    }


    
    public static String lineToHump(String str) {
        str = str.toLowerCase();
        Matcher matcher = linePattern.matcher(str);
        StringBuffer sb = new StringBuffer();
        while (matcher.find()) {
            matcher.appendReplacement(sb, matcher.group(1).toUpperCase());
        }
        matcher.appendTail(sb);
        return sb.toString();
    }

}

@Test
public void testPT(){

    Source source = new Source();
    source.setUpper("upper");
    source.setHigh_and_down("highanddown");
    source.setLOWER("lower");
    source.setSourceName("sourceName");
    
    System.out.println(source.toString());
    Target target = (Target) PropertiesTransformUtils.copy(source,Target.class);
    System.out.println(target.toString());

}

测试结果

Source(sourceName=sourceName, LOWER=lower, upper=upper, high_and_down=highanddown)
Target(targetName=sourceName, lower=lower, UPPER=upper, highAndDown=highanddown)