通过getter实现依赖注入

依赖注入是面向接口编程的前提，将对象的使用和对象的创建分离。使用者只需知道接口，而不必关心具体实现是哪个类。

例如：

public interface Job {
  public boolean doJob();
}

public class SweepJob {

  private int garbage = 10;

  public boolean doJbo() {
    System.out.println("扫地");
    garbage--;
    return garbage < 3;
  }
}

public class Worker {

  private Job job;

  public void work() throws Exception {
    while (!job.doJob()) {
      System.out.println("未完成，抱怨");
      Thread.sleep(100);
    }
  }
  
}

Worker依赖job，而不依赖SweepJob，但是Worker有必须取到一个SweepJob对象，这时就需要一个外部的容器来注入，Worker也要做相应的修改来接收注入。
1. 构造注入

public class Worker {

  private Job job;

  public Worker(Job job) {
    this.job = job;
  }
  ...
}

public class AppContext {
  
  private SweepJob job;
  private Worker worker;

  public void createBeans() {
    job = new SweepJob();
    worker = new Worker(job);
  }
}

2. setter注入

public class Worker {
  
  private Job job;

  public void setJob(Job job) {
    this.job = job;
  }
  ...
}

public class AppContext {
  
  private SweepJob job;
  private Worker worker;

  public void createBeans() {
    job = new SweepJob();
    worker = new Worker();
    worker.setJob(job);
  }
}

3. getter注入，也是写这篇日志的目的所在，今天看webx框架了解到的，感觉很有新意。

public abstruct class Worker {
  
  public abstruct Job getJob();
  
  public void work() throws Exception {
    while (!getJob().doJob()) {
      System.out.println("未完成，抱怨");
      Thread.sleep(100);
    }
  }
}

public class AppContext {
  
  private SweepJob job;
  private Worker worker;

  public void createBeans() {
    job = new SweepJob();
    worker = new Worker() {
      public Job getJob() {
        return job;
      }
    };
  }
}