Guice 简明教程
Google Guice - Optional Injection
注入是将依赖注入到对象中的一个过程。可选注入意味着在存在依赖项时注入该依赖项。方法和字段注入可能是可选的依赖项，并且在不存在依赖项时应该具有一些默认值。请参见以下示例。
Injection is a process of injecting dependeny into an object. Optional injection means injecting the dependency if exists. Method and Field injections may be optionally dependent and should have some default value if dependency is not present. See the example below.
Example
创建名为 GuiceTester 的 Java 类。
Create a java class named GuiceTester.
GuiceTester.java
import com.google.inject.AbstractModule;
import com.google.inject.Guice;
import com.google.inject.ImplementedBy;
import com.google.inject.Inject;
import com.google.inject.Injector;
import com.google.inject.name.Named;
public class GuiceTester {
public static void main(String[] args) {
Injector injector = Guice.createInjector(new TextEditorModule());
TextEditor editor = injector.getInstance(TextEditor.class);
editor.makeSpellCheck();
}
}
class TextEditor {
private SpellChecker spellChecker;
@Inject
public TextEditor( SpellChecker spellChecker) {
this.spellChecker = spellChecker;
}
public void makeSpellCheck(){
spellChecker.checkSpelling();
}
}
//Binding Module
class TextEditorModule extends AbstractModule {
@Override
protected void configure() {}
}
@ImplementedBy(SpellCheckerImpl.class)
interface SpellChecker {
public void checkSpelling();
}
//spell checker implementation
class SpellCheckerImpl implements SpellChecker {
private String dbUrl = "jdbc:mysql://localhost:5326/emp";
public SpellCheckerImpl(){}
@Inject(optional=true)
public void setDbUrl(@Named("JDBC") String dbUrl){
this.dbUrl = dbUrl;
}
@Override
public void checkSpelling() {
System.out.println("Inside checkSpelling." );
System.out.println(dbUrl);
}
}