关于@SneakyThrows使用

• 1 异常引入
• 2 @SneakyThrows
• • • • 1 SneakyThrows注解的源码
      • 2使用案例

关于@SneakyThrows注解的使用,主要是消除代码中异常处理代码.

Java中异常Throwable分为两类, 一种是Exception类,称为受检异常(Checked Exception), 第二种是RuntimeException类, 运行时异常.

Exception类异常,强制要求方法抛出可能出现的异常,调用者必须处理这个异常. 一般在代码中,程序员通过捕获异常,再包一层RuntimeException,向外抛出.(常见如Spring源码中)

@Target({ElementType.METHOD, ElementType.CONSTRUCTOR})
@Retention(RetentionPolicy.SOURCE)
public @interface SneakyThrows {
	
	Class[] value() default java.lang.Throwable.class;
	
	//The fully qualified name is used for java.lang.Throwable in the parameter only. This works around a bug in javac:
	//   presence of an annotation processor throws off the type resolver for some reason.
}

public class SneakyThrowDemo {

    // 方法主动声明可能出现的异常
    public void test1() throws IllegalAccessException, InstantiationException {
        SneakyThrowDemo sneakyThrowDemo = SneakyThrowDemo.class.newInstance();
    }

    // 使用SneakyThrows注解
    @SneakyThrows
    public void test2() {
        SneakyThrowDemo sneakyThrowDemo = SneakyThrowDemo.class.newInstance();
    }

    // test2方法的编译结果
    public void test3() {
        try {
            SneakyThrowDemo sneakyThrowDemo = SneakyThrowDemo.class.newInstance();
        } catch (Throwable e) {
            // 调用Lombok方法转化为RuntimeException
            throw Lombok.sneakyThrow(e);
        }
    }

}

其中Lombok.sneakyThrow()方法

		
public static RuntimeException sneakyThrow(Throwable t) {
		if (t == null) throw new NullPointerException("t");
		return Lombok.sneakyThrow0(t);
	}

	// 对返回参数做了强转为T类型
	private static  T sneakyThrow0(Throwable t) throws T {
		throw (T)t;
	}

整个处理过程中, 最重要的是throw (T)t, 使用泛型,将传入的Throwable强转为RuntimeException异常.

虽然, 我们抛出的异常不是RuntimeException,但是可以骗过javac编译器,泛型最后存储为字节码文件时并没有泛型信息.