别人说烂了的stream api不就不想赘述了，我想和大家分享一下，如何用函数式编程来简化我们的开发，想说点不一样的东西
转载链接
简化事务
对于事务而言，应该粒度越小越好，并且读写逻辑应该分开，只在写的逻辑上执行事务，可以用函数式编程来简化抽去写逻辑这一步
@Service
public class TransactionService {@Transactionalpublic void process(ThrowExceptionRunnable runnable){try {runnable.run();}catch (Exception e){new RuntimeException(e);}}
}//使用方式
public void regist(String username){User user = userService.findByUserName(username);if(user != null) return;//执行事务 注册用户 开通余额账号transactionService.process(() -> {userService.save(new User(username));balanceService.save(new Balance(username));});
}
赋予方法重试能力
public static void retryFunction(ThrowExceptionRunnable runnable, int time) {while (true) {try {runnable.run();return;} catch (Exception e) {time--;if (time <= 0) throw new RuntimeException(e);}}}public static <T, R> R retryFunction(ThrowExceptionFunction<T, R> function, T t, int time) {while (true) {try {return function.apply(t);} catch (Exception e) {time--;if (time <= 0) throw new RuntimeException(e);}}}public static <T, U, R> R retryFunction(ThrowExceptionBiFunction<T, U, R> function, T t, U u, int time) {while (true) {try {return function.apply(t, u);} catch (Exception e) {time--;if (time <= 0) throw new RuntimeException(e);}}}public static void main(String[] args) {//http调用，失败会重试3次retryFunction(()->http.call(),3);//把数字1转成数字 失败会重试三次String s = retryFunction(String::valueOf, 1, 3);String ss = retryFunction(i -> String.valueOf(i), 1, 3);}
赋予函数缓存能力
public static <T, R> R cacheFunction(Function<T, R> function, T t, Map<T, R> cache) {R r = cache.get(t);if (r != null) return r;R result = function.apply(t);cache.put(t,result);return result;
}public static void main(String[] args) {Map<String,User> cache = new HashMap<Integer, User>();String username = "张三";//不走缓存cacheFunction(u -> userService.findByUserName(u),username,cache);//走缓存cacheFunction(u -> userService.findByUserName(u),username,cache);}
赋予函数报错返回默认值能力
public static <T, R> R computeOrGetDefault(ThrowExceptionFunction<T, R> function, T t, R r) {try {return function.apply(t);} catch (Exception e) {return r;}}public static <R> R computeOrGetDefault(ThrowExceptionSupplier<R> supplier,R r){try {return supplier.get();} catch (Exception e) {return r;}}public static void main(String[] args) {//返回0computeOrGetDefault(i -> {if (i < 0) throw new RuntimeException();else return i;}, -1, 0);//返回5computeOrGetDefault(i -> {if (i < 0) throw new RuntimeException();else return i;},5,0);}
赋予函数处理异常的能力
public static <T, R> R computeAndDealException(ThrowExceptionFunction<T, R> function, T t, Function<Exception, R> dealFunc) {try {return function.apply(t);} catch (Exception e) {return dealFunc.apply(e);}}public static <T, U, R> R computeAndDealException(ThrowExceptionBiFunction<T,U, R> function, T t, U u,Function<Exception, R> dealFunc) {try {return function.apply(t,u);} catch (Exception e) {return dealFunc.apply(e);}}public static <R> R computeAndDealException(ThrowExceptionSupplier<R> supplier, Function<Exception, R> dealFunc) {try {return supplier.get();} catch (Exception e) {return dealFunc.apply(e);}}public static void main(String[] args) {//返回异常message的hashcodeInteger integer = computeAndDealException(i -> {if (i < 0) throw new RuntimeException("不能小于0");else return i;}, -1, e -> e.getMessage().hashCode());System.out.println(integer);}
赋予函数记录日志能力
public static <T, R> R logFunction(Function<T, R> function, T t, String logTitle) {long startTime = System.currentTimeMillis();log.info("[[title={}]],request={},requestTime={}", logTitle, t.toString(),LocalDateTime.now().format(DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss")));R apply = function.apply(t);long endTime = System.currentTimeMillis();log.info("[[title={}]],response={},spendTime={}ms", logTitle, apply.toString(), endTime - startTime);return apply;
}public static void main(String[] args) {logFunction(String::valueOf,"s","String.valueOf");
}
自定义函数接口
@FunctionalInterfacepublic interface ThrowExceptionFunction<T, R> {R apply(T t) throws Exception;}@FunctionalInterfacepublic interface ThrowExceptionBiFunction<T, U, R> {R apply(T t, U u) throws Exception;}@FunctionalInterfacepublic interface ThrowExceptionSupplier<T> {T get() throws Exception;}@FunctionalInterfacepublic interface ThrowExceptionRunnable {void run() throws Exception;}
Q:为什么要自定义函数接口
A:自带的函数接口无法处理检查异常，遇见带检查异常的方法会报错
我哪些场景用到了？
链式取数
在翻译php代码的时候我们常常遇到如下情况
$s = a.b.c.d.e.f.g
然后翻译成java代码的时候是这样的
String s = a.getB().getC().getD().getE().getF().getG();
有啥问题？没有没有判空，只要中间有一层为空，那么就是NPE，要是去写判空逻辑的话，真是要了命了
这时我们就可以用上上面提到的骚操作了
代码改写
String s = computeOrGetDefault(()->a.getB().getC().getD().getE().getF().getG(),"");
)
