SingleFlight模式

本文主要是介绍SingleFlight模式，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

SingleFlight

在Java中实现SingleFlight模式，可以通过使用ConcurrentHashMap和CompletableFuture来管理并发请求。以下是一个示例代码，展示了如何在Java中实现SingleFlight模式：

示例代码

import java.util.concurrent.CompletableFuture;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.TimeUnit;public class SingleFlight<T> {private final ConcurrentHashMap<String, CompletableFuture<T>> flightMap = new ConcurrentHashMap<>();public CompletableFuture<T> doRequest(String key, RequestFunction<T> requestFunction) {CompletableFuture<T> future = flightMap.computeIfAbsent(key, k -> {CompletableFuture<T> newFuture = new CompletableFuture<>();requestFunction.apply().whenComplete((result, throwable) -> {if (throwable != null) {newFuture.completeExceptionally(throwable);} else {newFuture.complete(result);}flightMap.remove(k);});return newFuture;});return future;}@FunctionalInterfacepublic interface RequestFunction<T> {CompletableFuture<T> apply();}public static void main(String[] args) {SingleFlight<String> singleFlight = new SingleFlight<>();for (int i = 0; i < 10; i++) {int finalI = i;CompletableFuture<String> future = singleFlight.doRequest("key", () -> {return CompletableFuture.supplyAsync(() -> {try {TimeUnit.SECONDS.sleep(2); // 模拟耗时操作} catch (InterruptedException e) {e.printStackTrace();}return "result from request " + finalI;});});future.whenComplete((result, throwable) -> {if (throwable != null) {System.out.println("Error: " + throwable.getMessage());} else {System.out.println("Request " + finalI + " got result: " + result);}});}try {TimeUnit.SECONDS.sleep(5); // 等待所有请求完成} catch (InterruptedException e) {e.printStackTrace();}}
}

代码解释

1. SingleFlight 类：管理并发请求的核心类。

   • flightMap：使用 ConcurrentHashMap 来存储正在进行的请求。
   • doRequest 方法：接收一个键和一个请求函数。如果相同键的请求已经在进行中，则返回相同的 CompletableFuture；否则，执行新的请求函数，并在请求完成后移除键。

2. RequestFunction 接口：定义了一个函数接口，用于表示异步请求函数。

3. main 方法：模拟了10个并发请求，所有请求都使用相同的键 "key"。由于使用了SingleFlight模式，这些请求会被合并为一个请求，结果会被共享。

运行结果

运行上述代码，你会看到所有请求共享同一个结果：

Request 0 got result: result from request 0
Request 1 got result: result from request 0
Request 2 got result: result from request 0
Request 3 got result: result from request 0
Request 4 got result: result from request 0
Request 5 got result: result from request 0
Request 6 got result: result from request 0
Request 7 got result: result from request 0
Request 8 got result: result from request 0
Request 9 got result: result from request 0

总结

通过使用 ConcurrentHashMap 和 CompletableFuture，我们可以在Java中实现SingleFlight模式，有效地减少对同一资源的重复请求，提高系统性能。

序列化和反序列化

package org.example.Serialize;import com.fasterxml.jackson.databind.annotation.JsonDeserialize;
import com.fasterxml.jackson.databind.annotation.JsonSerialize;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;import java.io.Serializable;@Data
@AllArgsConstructor
@NoArgsConstructor
@JsonSerialize(using = StudentSerializer.class)
@JsonDeserialize(using = StudentDeserializer.class)
public class Student implements Serializable {private static final long serialVersionUID = 1L;private String name;private int age;
}

package org.example.Serialize;import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.databind.JsonSerializer;
import com.fasterxml.jackson.databind.SerializerProvider;import java.io.IOException;public class StudentSerializer extends JsonSerializer<Student> {@Overridepublic void serialize(Student student, JsonGenerator jsonGenerator, SerializerProvider serializerProvider) throws IOException {jsonGenerator.writeStartObject();jsonGenerator.writeStringField(student.getClass().getSimpleName(), "学生姓名=" + student.getName() + ",年龄=" + student.getAge());jsonGenerator.writeEndObject();}
}

package org.example.Serialize;import com.fasterxml.jackson.core.JsonParser;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.DeserializationContext;
import com.fasterxml.jackson.databind.JsonDeserializer;
import com.fasterxml.jackson.databind.JsonNode;import java.io.IOException;
import java.lang.reflect.Constructor;public class StudentDeserializer extends JsonDeserializer<Student> {@Overridepublic Student deserialize(JsonParser jsonParser, DeserializationContext deserializationContext) throws IOException, JsonProcessingException {JsonNode node = jsonParser.getCodec().readTree(jsonParser);String text = node.get(Student.class.getSimpleName()).asText();System.out.println("反序列化中：" + text + " " + Student.class.getSimpleName());String[] elements = text.split(",");Student student = new Student();for (String element : elements) {String[] keyVal = element.split("=");if (keyVal[0].equals("学生姓名")) {student.setName(keyVal[1]);}if (keyVal[0].equals("年龄")) {student.setAge(Integer.parseInt(keyVal[1]));}}return student;}
}

package org.example.Serialize;import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;public class SerializeTest {public static void main(String[] args) throws JsonProcessingException {ObjectMapper objectMapper = new ObjectMapper();Student student = new Student("hi", 20);String stuStr = objectMapper.writeValueAsString(student);System.out.println(stuStr);Student stuRes = objectMapper.readValue(stuStr, Student.class);System.out.println(stuRes);}
}

运行结果：

{"Student":"学生姓名=hi,年龄=20"}
反序列化中：学生姓名=hi,年龄=20 Student
Student(name=hi, age=20)Process finished with exit code 0

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