mybatis学习-设计模式::builder模式（1）

学习设计模式，也是读码的一个乐趣。
从mybatis的基础代码，看看builder模式怎么玩

public class Environment {
  private String id;
  private TransactionFactory transactionFactory;
  private DataSource dataSource;

  public Environment(String id, TransactionFactory transactionFactory, DataSource dataSource) {
    this.id = id;
    this.transactionFactory = transactionFactory;
    this.dataSource = dataSource;
  }

  private Environment() {
  }

  public static class Builder {
    private Environment environment = new Environment();

    public Builder(String id, TransactionFactory transactionManager, DataSource dataSource) {
      environment.id = id;
      environment.transactionFactory = transactionManager;
      environment.dataSource = dataSource;
    }

    public Builder transactionFactory(TransactionFactory transactionFactory) {
      environment.transactionFactory = transactionFactory;
      return this;
    }

    public Builder dataSource(DataSource dataSource) {
      environment.dataSource = dataSource;
      return this;
    }

    public String id() {
      return environment.id;
    }

    public Environment build() {
      return environment;
    }

  }

  public String getId() {
    return id;
  }

  public TransactionFactory getTransactionFactory() {
    return transactionFactory;
  }

  public DataSource getDataSource() {
    return dataSource;
  }

}

小结

这种实现builder模式的要点:
1.被构建对象，构造函数私有化

private Environment() {
  }

2.public static 静态内部类

public static class Builder

3.大部分方法返回Builder本身，方便链式操作

Builder dataSource(xxx)
Builder transactionFactory(xxx)

4.通过上述复制构造后，返回真正构建的对象

public Environment build() {
      return environment;
    }

学而时习之 ：-)