JavaEE6规范CDI教程第四部分



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原文链接:http://code.google.com/p/jee6-cdi/wiki/DependencyInjectionAnIntroductoryTutorial 
本部分讲述@Producer。 
1. 使用@Producer来决定如何创建
可能你希望从AutomatedTellerMachineImpl中把选取传输器的方法分离出来。 
你可以创建一个Producer方法来决定创建和选取传输器，看下面的实例： 
例 1. TransportFactory决定使用/创建哪个传输器
package org.cdi.advocacy;
import javax.enterprise.inject.Produces;
public class TransportFactory {
        
        private boolean useJSON = true;
        private boolean behindFireWall = true;
        
        @Produces ATMTransport createTransport() {
                //Look up config parameters in some config file or LDAP server or database
                System.out.println("ATMTransport created with producer makes decisions");
                
                if (behindFireWall) {
                        if (useJSON) {
                                System.out.println("Created JSON transport");
                                return new JsonRestAtmTransport();
                        } else {
                                System.out.println("Created SOAP transport");
                                return new SoapAtmTransport();
                        }
                } else {
                        System.out.println("Created Standard transport");
                        return new StandardAtmTransport();
                }
        }
}

把创建动作从AutomatedTellerMachineImpl代码中分离出来是比较高级的做法。 
可能你不总是这么做，但是如果是的话，producer可以帮助你。 
输出和前面的一样。 
Output 
ATMTransport created with producer makes decisions
Created JSON transport
deposit called
communicating with bank via JSON REST transport
2. 在@Producer中使用限定词来决定如何创建
这个例子在最后构建 
你同样可以吧注入项作为参数传入到producer中，如下： 
例 2. TransportFactory决定使用/创建哪个传输器
package org.cdi.advocacy;
import javax.enterprise.inject.Produces;
public class TransportFactory {
        
        private boolean useJSON = true;
        private boolean behindFireWall = true;
        
        @Produces ATMTransport createTransport( @Soap ATMTransport soapTransport, 
                                                @Json ATMTransport jsonTransport) {
                //Look up config parameters in some config file
                System.out.println("ATMTransport created with producer makes decisions");
                
                if (behindFireWall) {
                        if (useJSON) {
                                System.out.println("return passed JSON transport");
                                return jsonTransport;
                        } else {
                                System.out.println("return passed SOAP transport");
                                return soapTransport;
                        }
         &nb
补充：软件开发 , Java ,