guava-retrying重试工具库的简单体验

官方文档地址: https://github.com/rholder/guava-retrying

    public static void main(String[] args) {
        Callable<Boolean> callable = new Callable<Boolean>() {
            private int i = 1;
            public Boolean call() throws Exception {
                 // do something useful here
                System.out.println("......" + i);
                if (i==1){
                    i ++ ;
                    throw new NullPointerException();
                }

                if (i == 2){
                    return true;
                }
                return true;
            }
        };

        Retryer<Boolean> retryer = RetryerBuilder.<Boolean>newBuilder()
                // 如果Callable结果为null,继续重试
                .retryIfResult(Predicates.<Boolean>isNull())
                // IOException,继续重试
                .retryIfExceptionOfType(IOException.class)
                // RuntimeException,继续重试
                .retryIfRuntimeException()
                // 指定重试策略,重试三次后停止
                .withStopStrategy(StopStrategies.stopAfterAttempt(3))
                .build();
        try {
            Boolean call = retryer.call(callable);
            System.out.println("call: " + call);
        } catch (RetryException e) {
            e.printStackTrace();
        } catch (ExecutionException e) {
            e.printStackTrace();
        }
    }

打印结果

......1
......2        // 第二次成功
call: true  // 打印callable的返回值

稍微修改一下代码

   public static void main(String[] args) {
        Callable<String> callable = new Callable<String>() {
            private int i = 1;
            public String call() throws Exception {
                 // do something useful here
                System.out.println("......" + i);
                if (i==1){
                    i ++ ;
                    throw new NullPointerException();
                }

                if (i == 2){
                    i ++ ;
                    return "error";
                }
                return "ok";
            }
        };

        Retryer<String> retryer = RetryerBuilder.<String>newBuilder()
                // 如果返回结果是error,继续重试
                .retryIfResult(Predicates.equalTo("error"))
                .retryIfExceptionOfType(IOException.class)
                .retryIfRuntimeException()
                .withStopStrategy(StopStrategies.stopAfterAttempt(3))
                .build();
        try {
            String call = retryer.call(callable);
            System.out.println("call: " + call);
        } catch (RetryException e) {
            e.printStackTrace();
        } catch (ExecutionException e) {
            e.printStackTrace();
        }
    }

打印结果

......1
......2  // 结果是error
......3  // 第三次成功
call: ok

重试的方法需要包装到Callable接口当中, 方法很多的话使用起来稍有不便,
可以使用AOP的方式来使用Retry
具体可以参考龙潭斋大神("http://techlog.cn")的这篇
http://www.techlog.cn/article/list/10183169