构建者builder模式

女爷i 2022-05-05 14:58 201阅读 0赞

遇到多个构造器参数时，我们可以考虑使用构建器Builder模式，相比于重叠构造器模式（定义多个重载的构造函数），JavaBeans模式(通过set方法挨个构造)，Builder构建者模式实现的方式更加优雅，对象更利于使用，在保证安全性的同时又兼顾了可读性。

一些著名的框架，比如okhttp, retrofit，安卓中各种原生的组件，比如dialog等随处可见Builder构建者模式。

接下来模仿okhttp用构建者模式来创建一个request对象：

/**
     * 用构建者builder模式模拟okhttp来创建request对象
     * Created by wujie on 2018/10/17.
     */
    public class Request {
        private final HttpUrl url;
        private final String method;
        private final Headers headers;
        private final RequestBody body;
    
        private Request(Builder builder) {
            url = builder.url;
            method = builder.method;
            headers = builder.headers.build();
            body = builder.body;
        }
    
    
        public static final class Builder {
            private HttpUrl url;
            private String method;
            private Headers.Builder headers;
            private RequestBody body;
    
            public Builder() {
                this.method = "GET";
                this.headers = new Headers.Builder();
            }
    
            public Builder url(String url) {
                if (url == null) throw new NullPointerException("url == null");
                // websocket URLs with HTTP URLs.
                if (url.regionMatches(true, 0, "ws:", 0, 3)) {
                    url = "http:" + url.substring(3);
                } else if (url.regionMatches(true, 0, "wss:", 0, 4)) {
                    url = "https:" + url.substring(4);
                }
                HttpUrl parsed = HttpUrl.parse(url);
                if (parsed == null) throw new IllegalArgumentException("unexpected url: " + url);
                return url(parsed);
            }
    
            public Builder url(HttpUrl url) {
                if (url == null) throw new NullPointerException("url == null");
                this.url = url;
                return this;
            }
    
            public Builder method(String method, RequestBody body) {
                if (method == null) throw new NullPointerException("method == null");
                if (method.length() == 0) throw new IllegalArgumentException("method.length() == 0");
                if (body != null && !HttpMethod.permitsRequestBody(method)) {
                    throw new IllegalArgumentException("method " + method + " must not have a request body.");
                }
                if (body == null && HttpMethod.requiresRequestBody(method)) {
                    throw new IllegalArgumentException("method " + method + " must have a request body.");
                }
                this.method = method;
                this.body = body;
                return this;
            }
    
            public Builder addHeader(String name, String value) {
                headers.add(name, value);
                return this;
            }
    
            public Builder get() {
                return method("GET", null);
            }
    
            public Builder head() {
                return method("HEAD", null);
            }
    
            public Builder post(RequestBody body) {
                return method("POST", body);
            }
    
            public Builder delete(RequestBody body) {
                return method("DELETE", body);
            }
    
            public Builder delete() {
                return delete(Util.EMPTY_REQUEST);
            }
    
            public Builder put(RequestBody body) {
                return method("PUT", body);
            }
    
            public Builder body(RequestBody body) {
                this.body = body;
                return this;
            }
    
            public Request build() {
                return new Request(this);
            }
        }
    }

链式调用也很方便：

public static void main(String[] args) {
            //链式调用
            Request request = new Request.Builder()
                    .url(HttpUrl.parse("https://blog.csdn.net/baiyicanggou_wujie"))
                    .addHeader("appid", "123456")
                    .addHeader("appsercet", "123456")
                    .post("填写你要post的requestBody")
                    .build();
        }

小技巧：idea可以下载innerBuilder或者lombok的@builder注解生成一般的builder代码。