《程序员修炼之道》-读书笔记六-工厂模式下的伪DI依赖注入

工厂类：

public class AgentFinderFactory {

  private static AgentFinderFactory singleton;

  private AgentFinderFactory() {
  }

  public static AgentFinderFactory getInstance() {
    if (singleton == null) {
      singleton = new AgentFinderFactory(); // 单例模式，保证此工厂类的唯一性
    }
    return singleton;
  }

  public AgentFinder getAgentFinder(String agentType) { // 根据类型，选择输出处理类
    AgentFinder finder = null;
    switch (agentType) {
    case "spreadsheet":
      finder = new SpreadsheetAgentFinder();
      break;
    case "webservice":
      finder = new WebServiceAgentFinder();
      break;
    default:
      finder = new WebServiceAgentFinder();
      break;
    }
    return finder;
  }
}

业务类：

public class HollywoodServiceWithFactory {

  public static List<Agent> getFriendlyAgents(String agentFinderType) {
    AgentFinderFactory factory = AgentFinderFactory.getInstance(); // 获取工厂类，此时工厂类初步加载
    AgentFinder finder = factory.getAgentFinder(agentFinderType); // 根据传入所有类型，获取所需操作对象
    List<Agent> agents = finder.findAllAgents(); // 执行业务
    List<Agent> friendlyAgents = filterAgents(agents, "Java Developers");
    return friendlyAgents;
  }

  public static List<Agent> filterAgents(List<Agent> agents, String agentType) { // 此方法不必关心
   .....
　　....

  }
}