java注解讲解与实用示例

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@Target(value = ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
public @interface Anno1 {
	//注解的变量，并且指定默认属性值
	boolean beNull() default false;
	
	int minVal() default 0;
	
	int maxVal() default Integer.MAX_VALUE;
}

@Getter
@Setter
public class AnnotationTest extends BaseLogger implements Serializable {

	private static final long serialVersionUID = 946475120194720568L;
	
	@Anno1(beNull = true)
	private String name;
	
	@Anno1(minVal=18)
	private Integer age;

	
	@SuppressWarnings("unchecked")
	public <T> T validateAnno(String param, Class<T> clazz) throws Exception{
		T test = (T)JSONObject.toBean(JSONObject.fromObject(param), clazz);
		//AnnotationTest test = new AnnotationTest();
		//testNull(test);
		for (Field f : test.getClass().getDeclaredFields()) {
			f.setAccessible(true);
			Anno1 anno1 = f.getAnnotation(Anno1.class);
			if( null != anno1){
				if( f.getType().equals(String.class) ){
					if(!anno1.beNull()){
						if(null == f.get(test)  || "".equals(f.get(test))){
							throw new Byron4jEcxeption(f.getName() + " 参数不能为空");
						};
					}
					
				}else if(f.getType().equals(Integer.class)){
					if(f.get(test) == null){
						throw new Byron4jEcxeption(f.getName() + " 参数不能为空");
					}
					
					Integer val = Integer.valueOf(String.valueOf(f.get(test)));
					if( val <= anno1.minVal() || val >= anno1.maxVal() ){
						throw new Byron4jEcxeption(f.getName() + " 参数应该大于" + anno1.minVal());
					}
				}
				
			}else{
				String value = String.valueOf(f.get(test));
				value = value.trim();
				if(f.getType().equals(String.class)){
					f.set(test, value);
				}
				if( null == value || "".equals(value) || "null".equals(value)){
					throw new Byron4jEcxeption(f.getName() + " 参数不能为空");
				}
			}

		}
		return test;
	}
	
	@Test
	public void testAnno(){
		String param = "{\"name\":\"\",\"age\":15}";
		try {
			System.out.println(validateAnno(param, AnnotationTest.class));
		} catch (Exception e) {
			log.error(e.getMessage());
			e.printStackTrace();
		}
	}
	
	@Deprecated
	public static void testNull(AnnotationTest test) {
		System.out.println(JSONObject.fromObject(test).toString());
	}
}