使用guice绑定一个番石榴供应商 [英] Binding a guava supplier using guice
问题描述
我想做这样的绑定
bind(Supplier<TestClass>).toProvider(Provider<Supplier<TestClass>>).in(Singleton.class);
该提供程序由外部函数返回,因此,在 toProvider()
内部,我调用该函数,并返回Provider < Supplier< TestClass>>
.
The provider is returned by an external function so, inside the toProvider()
, I call that function and it returns Provider<Supplier<TestClass>>
.
供应商来自番石榴,这样做的原因是,有一个与TestClass相关的文件,我需要读取该文件并将这些值分配给TestClass的各个字段.
The supplier is from guava, the reason to do this kind of thing is, there is a file associated with the TestClass and I need to read that file and assign those values to the respective fields of TestClass.
该文件在运行时发生更改,因此我需要一种方法来刷新存储在TestClass中的值.要做我曾经使用过的番石榴供应商.番石榴供应商有一个get方法,当调用该get方法时,如果我使用 memoizeWithExpiration()
创建实例,则它会检查TTL值,如果传递了,则可以指定一个lambda函数来读取文件并分配值.
And that file change at run time, So I need a way to refresh the values stored in TestClass. To-Do that guava supplier I used. Guava supplier has a get method and when that get method is called, if I used memoizeWithExpiration()
to create the instance then it checks the TTL value and if it passed, then I can specify a lambda function to read the file and assign values.
所以我需要像这样注入 Supplier< TestClass>
So I need to inject Supplier<TestClass>
like this
@Inject
Supplier<TestClass> someClassSupplier;
但是与Guice进行绑定使我感到困惑.
But For doing that binding with Guice is confusing for me.
推荐答案
您可以使用以下类型的代码执行所需的操作:
You can use the following kind of code to do what you want:
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,在您的课堂上:
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
}
}
您请求执行此操作的通用方法,因此在这里,请检查 bindSupplier
方法:
You requested for a generic way of doing this, so here it is, check the bindSupplier
method:
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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