使用guice绑定Guava供应商

mkshixfv  于 2021-07-03  发布在  Java
关注(0)|答案(1)|浏览(413)

我想做这样的装订,

bind(Supplier<TestClass>).toProvider(Provider<Supplier<TestClass>>).in(Singleton.class);

提供程序由外部函数返回,因此 toProvider() ,我调用该函数,它返回provider <Supplier<TestClass>> .
供应商来自guava,这样做的原因是,有一个与testclass相关联的文件,我需要读取该文件并将这些值赋给testclass的相应字段。
文件在运行时会发生更改,所以我需要一种方法来刷新testclass中存储的值。做我用过的Guava供应商。guava供应商有一个get方法,当调用该get方法时,如果我使用 memoizeWithExpiration() 为了创建示例,它检查ttl值,如果传递了,那么我可以指定lambda函数来读取文件并赋值。
所以我需要注射 Supplier<TestClass> 这样地

@Inject
Supplier<TestClass> someClassSupplier;

但是用guice绑定对我来说很混乱。

tktrz96b

tktrz96b1#

可以使用以下类型的代码执行所需操作:

class ServiceModule extends AbstractModule {
  private TestClass readTestClassFromFile() {
    return new TestClass();
  }

  // Cache an instance for 5 seconds.
  private final Supplier<TestClass> testClassSupplier = Suppliers.memoizeWithExpiration(this::readTestClassFromFile, 5, SECONDS);

  @Provides TestClass provideTestClass() { // Don't declare as singleton
    return testClassSupplier.get();
  }
}

然后,在你的课堂上:

class Service {

  @Inject
  Provider<TestClass> testClassProvider; // Inject the provider, not the instance itself, or any supplier.

  void doSomething() throws Exception {
    TestClass a = testClassProvider.get();
    TestClass b = testClassProvider.get();

    Thread.sleep(6000); // Sleep for 6 seconds

    TestClass c = testClassProvider.get();

    System.out.println(a == b); // Prints true
    System.out.println(a == c); // Prints false
  }
}

你要求一个通用的方法来做这件事,所以在这里,检查 bindSupplier 方法:

import static com.google.common.base.Suppliers.memoizeWithExpiration;

import com.google.inject.*;
import java.util.concurrent.TimeUnit;
import java.util.function.Supplier;

public class Main {

  public static void main(String[] args) throws Exception {
    Guice.createInjector(new ServiceModule())
        .getInstance(Service.class)
        .doSomething();
  }

  static class ServiceModule extends AbstractModule {
    Dependency createDependency() { return new Dependency(); }

    // For Java 8+
    private <T> void bindSupplier(Class<T> type, Supplier<? extends T> supplier) {
      // Definitely avoid .in(Singleton.class) because you want the scope to be defined by the Supplier.
      bind(type).toProvider(supplier::get);
    }

// For Java 7 and less
//    private <T> void bindSupplier(Class<T> type, final Supplier<? extends T> supplier) {
//      bind(type).toProvider(new Provider<T>() {
//          @Override public T get() { return supplier.get(); }
//        });
//    }

    @Override protected void configure() {
      bindSupplier(Dependency.class,
          memoizeWithExpiration(this::createDependency, 3, TimeUnit.SECONDS));
    }

  }

  static class Dependency {}

  static class Service {

    @Inject Provider<Dependency> dependencyProvider;

    void doSomething() throws InterruptedException {
      Dependency a = dependencyProvider.get();
      Dependency b = dependencyProvider.get();
      Thread.sleep(4000);
      Dependency c = dependencyProvider.get();
      System.out.printf("a == b ? %s%n", a == b); // true
      System.out.printf("a == c ? %s%n", a == c); // false
    }
  }
}

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