Why provider is in different scope by defining it in two similar ways ?

[Michael]

Hi All,

 

I found a very interesting thing about the scope of the provider. Here is the code of BaseModelProvider

 

public class BaseModelProvider implements Provider<Model> {

private int num;

@Override
 public Model get() {
  System.out.println(num++);
  return new Model();
 }

--------------------------------------------------------------------

this.bind(Model.class).annotatedWith(Names.named("index")).toProvider(new BaseModelProvider());

 

This way gives : 1,2,3,4,5,6.....(in singleton scope)

---------------

this.bind(Model.class).annotatedWith(Names.named("index")).toProvider(BaseModelProvider.class);

This way gives : 0,0,0,0,0.....(in request scope)

 

 

I don't understand the different about this two definitions. So anybody knows how it works ?  many thanks!

 

BTW: I just want bind many providers dynamically within a loop, So I am using the .toProvider(Prvider<? extends Model> instance).

 

[Thomas Broyer]

On Saturday, January 5, 2013 11:34:22 AM UTC+1, Michael wrote:

Hi All,

 

I found a very interesting thing about the scope of the provider. Here is the code of BaseModelProvider

 

public class BaseModelProvider implements Provider<Model> {

private int num;

@Override
 public Model get() {
  System.out.println(num++);
  return new Model();
 }

--------------------------------------------------------------------

this.bind(Model.class).annotatedWith(Names.named("index")).toProvider(new BaseModelProvider());

 

This way gives : 1,2,3,4,5,6.....(in singleton scope)

---------------

this.bind(Model.class).annotatedWith(Names.named("index")).toProvider(BaseModelProvider.class);

This way gives : 0,0,0,0,0.....(in request scope)

 

 

I don't understand the different about this two definitions. So anybody knows how it works ?  many thanks!

In the first case, you provide a Provider instance, so only this instance will be used, making it a de-facto singleton.

In the second case, Guice will create the provider just like any other object. If you want it to be a singleton, then annotate it with @Singleton or bind it as a singleton with "bind(BaseModelProvider.class).in(Singleton.class)".

This is similar to "bind(Foo.class).toInstance(new MyFoo())" vs. "bind(Foo.class).to(MyFoo.class)".

[Mikhail Mazursky]

The first way you implicitly bind to an instance (so provider is
singleton itself - guice will never instantiate it):
bind(BaseModelProvider.class).toInstance(new BaseModelProvider());
bind(Model.class).annotatedWith(Names.named("index")).toProvider(BaseModelProvider.class);

The second way you implicitly bind in prototype scope (no scope):
bind(BaseModelProvider.class);
bind(Model.class).annotatedWith(Names.named("index")).toProvider(BaseModelProvider.class);

If you want your providers to be in some scope then you should let
Guice create them for you and either annotate them with scoping
annotation (e.g. with @Singleton) or bind them in scope (like
bind(BaseModelProvider.class).in(Singleton.class);).

2013/1/5 Michael <fuh...@gmail.com>:

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[Michael]

Many thanks! Much more clear.
在 2013年1月5日星期六UTC+8下午9时31分33秒，Thomas Broyer写道：

[Michael]

Many thanks! Much more clear.

在 2013年1月5日星期六UTC+8下午8时14分48秒，Mikhail Mazursky写道：