The point of confusion might be that you're expecting Guice to generate a
Provider. It is you who has to write an implementing Provider<LogFileEntry>
class.
You then need to tell Guice to use a certain Provider when asked for a
certain class.
For instance, you'd implement one Provider for clear text log files:
public class ClearTextLogFileEntryProvider implements Provider<LogFileEntry>
{
public LogFileEntry get() {
return new ClearTestLogFileEntry();
}
}
or one for encrypted log files:
public class EncryptedLogFileEntryProvider implements Provider<LogFileEntry>
{
public LogFileEntry get() {
return new EnctryptedLogFileEntry();
}
}
There is no magic here, so you have to tell Guice when to use which
Provider:
Guice.createInjector(new Module() {
public void configure(Binder binder) {
binder.bind(LogFileEntry.class).toProvider(ClearTextLogFileProvider.class);
//use clear text logs
}
});
With the above binding, you're telling Guice that the
ClearTextLogFileProvider.class is the source of LogFileEntry's. When the
Injector encounters a class requiring a LogFileEntry or
LogFileEntryProvider, it will use ClearTextLogFileProvider. For instance:
public class SomethingInteresting {
private Provider<LogFileEntry> provider;
private LogFileEntry log;
/*
* The ClearTextLogFileProvider.class would be used
* when injecting both of the following dependencies
*/
@Inject SomethingInteresting( Provider<LogFileEntry>
logFileEntryProvider, LogFileEntry log) {
this.provider = logFileEntryProvider;
this.log = log;
}
}
Hope that helps.
-Brandon
On Fri, Aug 14, 2009 at 3:47 AM, Anthony MULLER <[email protected]>wrote:
> The "Provider<LogFileEntry>" instance is injected in the constructor and
> set as an attribute of the LogFileTransactionLog object.
>
> After, that depends on how is implemented the provider itself. When get()
> method is called, the provider implementation can return a new instance
> LogFileEntry, or always the same (quite strange in this case ?)
>
> What's your problem about that?
>
> Anthony MÜLLER
>
> 2009/8/14 zhaoyi <[email protected]>
>
>
>> Can anyone help me on this? thanks.
>>
>> On Aug 10, 2:38 am, zhaoyi <[email protected]> wrote:
>> > I have read the article "Providers for multiple instances" in this
>> > linkhttp://code.google.com/p/google-guice/wiki/InjectingProviders.
>> > The example shown is:
>> > public class LogFileTransactionLog implements TransactionLog {
>> >
>> > private final Provider<LogFileEntry> logFileProvider;
>> >
>> > @Inject
>> > public LogFileTransactionLog(Provider<LogFileEntry> logFileProvider)
>> > {
>> > this.logFileProvider = logFileProvider;
>> > }
>> >
>> > public void logChargeResult(ChargeResult result) {
>> > LogFileEntry summaryEntry = logFileProvider.get();
>> > summaryEntry.setText("Charge " + (result.wasSuccessful() ?
>> > "success" : "failure"));
>> > summaryEntry.save();
>> >
>> > if (!result.wasSuccessful()) {
>> > LogFileEntry detailEntry = logFileProvider.get();
>> > detailEntry.setText("Failure result: " + result);
>> > detailEntry.save();
>> > }
>> > }
>> >
>> > There are two places to call logFileProvider.get() method. Are they
>> > return the same type of LogFileEntry? If they return different type of
>> > LogFileEntry, how does logFileProvider know which type is requested?
>> >
>> > thanks.
>>
>>
>
> >
>
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