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引入guava包：

       
    
     com.google.guava
        
    
     guava
        
    
     11.0.2
    
   

public class PreconditionsExample {    public static void main(String[] args) {        /**         * 对象判空处理         */        UserInfo userInfo = null;        Preconditions.checkNotNull(userInfo, "userInfo不能为null");        /**         * List对象判空处理         */        List
   
     list = Lists.newArrayList();        Preconditions.checkNotNull(list, "传入的list不能为null");        /**         * 数值类型判断处理         */        Long projectId = -12L;        Preconditions.checkNotNull(projectId, "projectId不能为null");        Preconditions.checkArgument(projectId > 0, "输入projectId必须大于0", projectId);    }        class UserInfo{        private String name;    }}
   

@Slf4jpublic class OptionalExample {    public static void main(String[] args) {        Optional
   
     userInfo = Optional.ofNullable(getUserInfo());        if (!userInfo.isPresent()){            log.info("userInfo is null");        }                Optional
    
      projectIdOptional = Optional.ofNullable(getProjectId());        Long projectId = projectIdOptional.orElse(0L); // 如果projectId为null时，这值为0    }        public static UserInfo getUserInfo() {        return null;    }        public static Long getProjectId() {        return null;    }        @Getter    @Setter    class UserInfo{        private String userName;    }}
    
   

       
    
     com.github.rholder
        
    
     guava-retrying
        
    
     2.0.0
    
   

@Slf4jpublic class RetryerExample {    public static void main(String[] args) throws Exception {        Retryer
   
     retryer = RetryerBuilder.
    
     newBuilder()                .retryIfResult(Predicates.
     
      isNull())    // 设置自定义段元重试源                .retryIfExceptionOfType(Exception.class)        // 设置异常重试源                .retryIfRuntimeException()                      // 设置异常重试源                .withStopStrategy(StopStrategies.stopAfterAttempt(5))   // 设置重试次数    设置重试超时时间？？？？                .withWaitStrategy(WaitStrategies.fixedWait(5L, TimeUnit.SECONDS)) // 设置每次重试间隔                .build();        Callable
      
        task = new Callable
       
        () {            int i = 0;            @Override            public Boolean call() throws Exception {                i++;                log.info("第{}次执行！", i);                if (i<3) {                    log.info("模拟执行失败");                    throw new IOException("异常");                }                return true;            }        };        try {            retryer.call(task);        } catch (ExecutionException e) {            log.error("error", e);        } catch (RetryException e) {            log.error("error", e);        }                Boolean result = task.call();        log.info("成功输出结果：{}", result);    }    }
       
      
     
    
   

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