mybatis源码中builder模式

例如XMLConfigBuilder这个类中：这种利用类不类，链式操作的，我们在编程中，值得借鉴

 Environment.Builder environmentBuilder = new Environment.Builder(id)
              .transactionFactory(txFactory)
              .dataSource(dataSource);
 configuration.setEnvironment(environmentBuilder.build());

Environement代码如下，

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

  public Environment(String id, TransactionFactory transactionFactory, DataSource dataSource) {
    if (id == null) {
      throw new IllegalArgumentException("Parameter 'id' must not be null");
    }
    if (transactionFactory == null) {
        throw new IllegalArgumentException("Parameter 'transactionFactory' must not be null");
    }
    this.id = id;
    if (dataSource == null) {
      throw new IllegalArgumentException("Parameter 'dataSource' must not be null");
    }
    this.transactionFactory = transactionFactory;
    this.dataSource = dataSource;
  }

  public static class Builder {
      private String id;
      private TransactionFactory transactionFactory;
      private DataSource dataSource;

    public Builder(String id) {
      this.id = id;
    }

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

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

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

    public Environment build() {
      return new Environment(this.id, this.transactionFactory, this.dataSource);
    }

  }

  public String getId() {
    return this.id;
  }

  public TransactionFactory getTransactionFactory() {
    return this.transactionFactory;
  }

  public DataSource getDataSource() {
    return this.dataSource;
  }

}