java异步处理同步化_java 异步查询转同步多种实现方式：循环等待，CountDownLatch，Spring Even...
異步轉(zhuǎn)同步
業(yè)務(wù)需求
有些接口查詢反饋結(jié)果是異步返回的，無法立刻獲取查詢結(jié)果。
正常處理邏輯
觸發(fā)異步操作，然后傳遞一個(gè)唯一標(biāo)識。
等到異步結(jié)果返回，根據(jù)傳入的唯一標(biāo)識，匹配此次結(jié)果。
如何轉(zhuǎn)換為同步
正常的應(yīng)用場景很多，但是有時(shí)候不想做數(shù)據(jù)存儲，只是想簡單獲取調(diào)用結(jié)果。
即想達(dá)到同步操作的結(jié)果，怎么辦呢？
思路
發(fā)起異步操作
在異步結(jié)果返回之前，一直等待(可以設(shè)置超時(shí))
結(jié)果返回之后，異步操作結(jié)果統(tǒng)一返回
循環(huán)等待
LoopQuery.java
使用 query()，將異步的操作 remoteCallback() 執(zhí)行完成后，同步返回。
public class LoopQuery implements Async {
private String result;
private static final Logger LOGGER = LogManager.getLogger(LoopQuery.class.getName());
@Override
public String query(String key) {
startQuery(key);
new Thread(new Runnable() {
@Override
public void run() {
remoteCallback(key);
}
}).start();
final String queryResult = endQuery();
LOGGER.info("查詢結(jié)果: {}", queryResult);
return queryResult;
}
/**
* 開始查詢
* @param key 查詢條件
*/
private void startQuery(final String key) {
LOGGER.info("執(zhí)行查詢: {}", key);
}
/**
* 遠(yuǎn)程的回調(diào)是等待是隨機(jī)的
*
* @param key 查詢條件
*/
private void remoteCallback(final String key) {
try {
TimeUnit.SECONDS.sleep(5);
} catch (InterruptedException e) {
e.printStackTrace();
}
this.result = key + "-result";
LOGGER.info("remoteCallback set result: {}", result);
}
/**
* 結(jié)束查詢
* @return 返回結(jié)果
*/
private String endQuery() {
while (true) {
if (null == result) {
try {
TimeUnit.MILLISECONDS.sleep(100);
} catch (InterruptedException e) {
e.printStackTrace();
}
} else {
return result;
}
}
}
}
main()
public static void main(String[] args) {
new LoopQuery().query("12345");
}
測試結(jié)果
18:14:16.491 [main] INFO com.github.houbb.thread.learn.aysnc.loop.LoopQuery - 執(zhí)行查詢: 12345
18:14:21.498 [Thread-1] INFO com.github.houbb.thread.learn.aysnc.loop.LoopQuery - remoteCallback set result: 12345-result
18:14:21.548 [main] INFO com.github.houbb.thread.learn.aysnc.loop.LoopQuery - 查詢結(jié)果: 12345-result
CountDownLatch
AsyncQuery.java
使用 CountDownLatch 類達(dá)到同步的效果。
import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.TimeUnit;
public class AsyncQuery {
private static final Logger LOGGER = LogManager.getLogger(AsyncQuery.class.getName());
/**
* 結(jié)果
*/
private String result;
/**
* 異步轉(zhuǎn)同步查詢
* @param key
*/
public void asyncQuery(final String key) {
final CountDownLatch latch = new CountDownLatch(1);
this.startQuery(key);
new Thread(new Runnable() {
@Override
public void run() {
LOGGER.info("遠(yuǎn)程回調(diào)線程開始");
remoteCallback(key, latch);
LOGGER.info("遠(yuǎn)程回調(diào)線程結(jié)束");
}
}).start();
try {
latch.await();
} catch (InterruptedException e) {
e.printStackTrace();
}
this.endQuery();
}
private void startQuery(final String key) {
LOGGER.info("執(zhí)行查詢: {}", key);
}
/**
* 遠(yuǎn)程的回調(diào)是等待是隨機(jī)的
* @param key
*/
private void remoteCallback(final String key, CountDownLatch latch) {
try {
TimeUnit.SECONDS.sleep(5);
} catch (InterruptedException e) {
e.printStackTrace();
}
this.result = key + "-result";
latch.countDown();
}
private void endQuery() {
LOGGER.info("查詢結(jié)果: {}", result);
}
}
main()
public static void main(String[] args) {
AsyncQuery asyncQuery = new AsyncQuery();
final String key = "123456";
asyncQuery.asyncQuery(key);
}
日志
18:19:12.714 [main] INFO com.github.houbb.thread.learn.aysnc.countdownlatch.AsyncQuery - 執(zhí)行查詢: 123456
18:19:12.716 [Thread-1] INFO com.github.houbb.thread.learn.aysnc.countdownlatch.AsyncQuery - 遠(yuǎn)程回調(diào)線程開始
18:19:17.720 [main] INFO com.github.houbb.thread.learn.aysnc.countdownlatch.AsyncQuery - 查詢結(jié)果: 123456-result
18:19:17.720 [Thread-1] INFO com.github.houbb.thread.learn.aysnc.countdownlatch.AsyncQuery - 遠(yuǎn)程回調(diào)線程結(jié)束
Spring EventListener
使用觀察者模式也可以。(對方案一的優(yōu)化)
此處結(jié)合 spring 進(jìn)行使用。
BookingCreatedEvent.java
定義一個(gè)傳輸屬性的對象。
public class BookingCreatedEvent extends ApplicationEvent {
private static final long serialVersionUID = -1387078212317348344L;
private String info;
public BookingCreatedEvent(Object source) {
super(source);
}
public BookingCreatedEvent(Object source, String info) {
super(source);
this.info = info;
}
public String getInfo() {
return info;
}
}
BookingService.java
說明：當(dāng) this.context.publishEvent(bookingCreatedEvent); 觸發(fā)時(shí)，
會被 @EventListener 指定的方法監(jiān)聽到。
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.ApplicationContext;
import org.springframework.context.event.EventListener;
import org.springframework.stereotype.Service;
import java.util.concurrent.TimeUnit;
@Service
public class BookingService {
@Autowired
private ApplicationContext context;
private volatile BookingCreatedEvent bookingCreatedEvent;
/**
* 異步轉(zhuǎn)同步查詢
* @param info
* @return
*/
public String asyncQuery(final String info) {
query(info);
new Thread(new Runnable() {
@Override
public void run() {
remoteCallback(info);
}
}).start();
while(bookingCreatedEvent == null) {
//.. 空循環(huán)
// 短暫等待。
try {
TimeUnit.MILLISECONDS.sleep(1);
} catch (InterruptedException e) {
//...
}
//2. 使用兩個(gè)單獨(dú)的 event...
}
final String result = bookingCreatedEvent.getInfo();
bookingCreatedEvent = null;
return result;
}
@EventListener
public void onApplicationEvent(BookingCreatedEvent bookingCreatedEvent) {
System.out.println("監(jiān)聽到遠(yuǎn)程的信息: " + bookingCreatedEvent.getInfo());
this.bookingCreatedEvent = bookingCreatedEvent;
System.out.println("監(jiān)聽到遠(yuǎn)程消息后: " + this.bookingCreatedEvent.getInfo());
}
/**
* 執(zhí)行查詢
* @param info
*/
public void query(final String info) {
System.out.println("開始查詢: " + info);
}
/**
* 遠(yuǎn)程回調(diào)
* @param info
*/
public void remoteCallback(final String info) {
System.out.println("遠(yuǎn)程回調(diào)開始: " + info);
try {
TimeUnit.SECONDS.sleep(2);
} catch (InterruptedException e) {
e.printStackTrace();
}
// 重發(fā)結(jié)果事件
String result = info + "-result";
BookingCreatedEvent bookingCreatedEvent = new BookingCreatedEvent(this, result);
//觸發(fā)event
this.context.publishEvent(bookingCreatedEvent);
}
}
測試方法
@RunWith(SpringJUnit4Cla***unner.class)
@ContextConfiguration(classes = SpringConfig.class)
public class BookServiceTest {
@Autowired
private BookingService bookingService;
@Test
public void asyncQueryTest() {
bookingService.asyncQuery("1234");
}
}
日志
2018-08-10 18:27:05.958 INFO [main] com.github.houbb.spring.lean.core.ioc.event.BookingService:84 - 開始查詢:1234
2018-08-10 18:27:05.959 INFO [Thread-2] com.github.houbb.spring.lean.core.ioc.event.BookingService:93 - 遠(yuǎn)程回調(diào)開始:1234
接收到信息: 1234-result
2018-08-10 18:27:07.964 INFO [Thread-2] com.github.houbb.spring.lean.core.ioc.event.BookingService:73 - 監(jiān)聽到遠(yuǎn)程的信息: 1234-result
2018-08-10 18:27:07.964 INFO [Thread-2] com.github.houbb.spring.lean.core.ioc.event.BookingService:75 - 監(jiān)聽到遠(yuǎn)程消息后: 1234-result
2018-08-10 18:27:07.964 INFO [Thread-2] com.github.houbb.spring.lean.core.ioc.event.BookingService:106 - 已經(jīng)觸發(fā)event
2018-08-10 18:27:07.964 INFO [main] com.github.houbb.spring.lean.core.ioc.event.BookingService:67 - 查詢結(jié)果: 1234-result
2018-08-10 18:27:07.968 INFO [Thread-1] org.springframework.context.support.GenericApplicationContext:993 - Closing org.springframework.context.support.GenericApplicationContext@5cee5251: startup date [Fri Aug 10 18:27:05 CST 2018]; root of context hierarchy
超時(shí)和空循環(huán)
空循環(huán)
空循環(huán)會導(dǎo)致 cpu 飆升
while(true) {
}
解決方式
while(true) {
// 小睡即可
TimeUnit.sleep(1);
}
超時(shí)編寫
不可能一直等待反饋，可以設(shè)置超時(shí)時(shí)間。
/**
* 循環(huán)等待直到獲取結(jié)果
* @param key key
* @param timeoutInSeconds 超時(shí)時(shí)間
* @param 泛型
* @return 結(jié)果。如果超時(shí)則拋出異常
*/
public T loopWaitForValue(final String key, long timeoutInSeconds) {
long startTime = System.nanoTime();
long deadline = startTime + TimeUnit.SECONDS.toNanos(timeoutInSeconds);
//1. 如果沒有新回調(diào)，或者 key 對應(yīng)元素不存在。則一直循環(huán)
while(ObjectUtil.isNull(map.get(key))) {
try {
TimeUnit.MILLISECONDS.sleep(5);
} catch (InterruptedException e) {
LOGGER.warn("Loop meet InterruptedException, just ignore it.", e);
}
// 超時(shí)判斷
long currentTime = System.nanoTime();
if(currentTime >= deadline) {
throw new BussinessException(ErrorCode.READ_TIME_OUT);
}
}
final T target = (T) map.get(key);
LOGGER.debug("loopWaitForValue get value:{} for key:{}", JSON.toJSON(target), key);
//2. 獲取到元素之后，需要移除掉對應(yīng)的值
map.remove(key);
return target;
}
代碼地址
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