Fred Faber wrote:
2010/1/20 Willi Schönborn <[email protected]
<mailto:[email protected]>>
Fred Faber wrote:
2010/1/20 Willi Schönborn <[email protected]
<mailto:[email protected]>
<mailto:[email protected]
<mailto:[email protected]>>>
Thanks for the reply, i left a comment below.
Fred Faber wrote:
Yeah in general this is not entirely an easy problem.
Without knowing more about your problem specifics, here are
some solutions:
First, you can always use what you have, with
Modules.override() to override the annotation binding:
class RealDbModule extends AbstractModule {
@Override
protected void configure() {
bind(...the db provider you show in your mail);
}
}
Module myTestDbModule = Modules.override(myRealDbModule)
.with(new AbstractModule() {
@Override
protected void configure() {
bind(Key.get(String.class,
Names.named("database.mysql.username")).toInstance("test");
}
}
and you can install this in your private module, or do what
you will with it.
That what i was thinking, but is there a nice way to retrieve
"test" from
a properties file instead of hardcoding it to the module?
I imagine so, sure, but that seems like it has solutions that
are independent of guice and more specific to how you want to
read the file. As far as design of the modules, "test"
doesn't need to be hardcoded and there can be any logic that
reads the file substituted in its place.
Reading a properties file on my own is exactly what i want to avoid ;)
Can i do:
binder.bind(Key.get(String.class,
Names.named("database.mysql2.username")).to(Key.get(String.class,
Names.named("database.mysql.username")); ?
This is the concept of a bridging binding, whereby the biding attached
to one Key is going to be bridged (effectively transfered, if you
will) to a binding attached to another key.
You can make this general by a simple class:
class BridgingProvider<T> implements Provider<T> {
private static <T> ScopingBindingBuider bindBridge(
Binder binder,
Key<T> keyToBridge,
Class<? extends Annotation> bridgeAnnotation) {
Provider<T> bindingProvider = new BridgingProvider(keyToBridge);
Key<T> bridgedKey =
Key.get(keyToBridge.getTypeLiteral(), bridgeAnnotation);
return binder.bind(keyToBridge).toProvider(bindingProvider);
}
private static final Key<T> keyToBridge;
@Inject
Injector injector;
private BridgingProvider(Key<T> keyToBridge) {
this.keyToBridge = keyToBridge;
}
@Override
public T get() {
T bridgedInstance injector.getInstance(keyToBridge);
return bridgedInstance;
}
}
and then:
BridgingProvider.bindBridge(
binder(),
Key.get(String.class, Names.named("database.mysql2.username")),
Names.named("database.mysql.username"));
Which will inject whatever is bound to "Key.get(String.class,
Names.named("database.mysql2.username"))" as the value when asked to
inject something with the key, "Key.get(String.class,
Names.named("database.mysql.username")).
-Fred
That looks great. I will give you feedback as soon as i tried it.
* * *
You can add a crufty solution, such as passing in a
constructor arg to your DbModule:
class DbModule extends AbstractModule {
private final DbModule(String annotationName) {
this.annotationName = annotationName;
}
@Override
protected void configure() {
bind(Database.class).toProvider(new
Provider<Database>() {
@Inject Injector injector;
@Override
public Database get() {
Named named = Names.named(annotationName);
Key<String> annotationKey =
Key.get(String.class, named);
String dbUser =
injector.getInstance(annotaitonKey);
return new MySqlDatabase(......);
}
}
I almost didn't want to suggest this, and I'll justify
it by
saying that I do it simply to illustrate why it's not a
great
solution:
1) because who knows through how many other classes you'll
need to propagate the constructor arg
2) because Guice isn't creating your MySqlDatabase instance
* * *
There are other methods along these lines as well.
With more
details I can probably suggest something more
appropriate for
your case.
2010/1/19 Willi Schönborn <[email protected]
<mailto:[email protected]>
<mailto:[email protected]
<mailto:[email protected]>>
<mailto:[email protected]
<mailto:[email protected]>
<mailto:[email protected]
<mailto:[email protected]>>>>
On 17/01/2010 12:14, Willi Schönborn wrote:
On 17/01/2010 00:18, Dhanji R. Prasanna wrote:
2010/1/17 Willi Schönborn
<[email protected]
<mailto:[email protected]>
<mailto:[email protected]
<mailto:[email protected]>>
<mailto:[email protected]
<mailto:[email protected]>
<mailto:[email protected]
<mailto:[email protected]>>>>
On 16/01/2010 18:02, Kartik Kumar wrote:
This may help.
http://code.google.com/p/google-guice/wiki/BindingAnnotations
No, i dont want to bind multiple
Implementations to the same
interface, i want to configure (!)
multiple instances of the same class
independently using
annotations (@Named).
You're referring to the robot legs problem:
http://code.google.com/p/google-guice/wiki/FrequentlyAskedQuestions
(look for "robot legs")
An idea? Anyone?
I managed to solve a part of the problem using
private
modules,
but there is something left i dont know
how to do:
Better example:
public interface Database
and
class MySqlDatabase implements Database {
@Named("database.mysql.username")
private String username;
}
Lets assume i actually want to work with two
different
mysql
databases and
i have a settings.properties which is bound using
Names.bindProperties() and contains:
database.mysql.username = test
database.mysql.second.username = user
I need a way to "override" a constant bound by
Names.bindProperties(...)
in a private module by using the value of another
constant binding.
E.g. I want to set the value of
"database.mysql.username" to the
value of
"database.mysql.second.username" in my private
module
without
the need to parse the properties file on my own.
Dhanji.
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