Android常用的模式

Builder构建模式

{% note primary %} 通过JavaBean对象给要构建的对象一一赋值，处理灵活，可分别初始化值和设置值。 {% endnote%}

public final class Request {
  final HttpUrl url;
  final String method;
  final Headers headers;
  final @Nullable RequestBody body;
  final Map<Class<?>, Object> tags;
  
  Request(Builder builder) {
    this.url = builder.url;
    this.method = builder.method;
    this.headers = builder.headers.build();
    this.body = builder.body;
    this.tags = Util.immutableMap(builder.tags);
  }
}

public static class Builder {
    HttpUrl url;
    String method;
    Headers.Builder headers;
    RequestBody body;

    public Builder() {
      this.method = "GET";
      this.headers = new Headers.Builder();
    }

    Builder(Request request) {
      this.url = request.url;
      this.method = request.method;
      this.body = request.body;
      this.tags = request.tags.isEmpty()
          ? Collections.<Class<?>, Object>emptyMap()
          : new LinkedHashMap<>(request.tags);
      this.headers = request.headers.newBuilder();
    }

    public Builder url(HttpUrl url) {
      if (url == null) throw new NullPointerException("url == null");
      this.url = url;
      return this;
    }

    public Request build() {
      if (url == null) throw new IllegalStateException("url == null");
      return new Request(this);
    }
  }