Builder模式，今天你用了嘛
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1.前言
在設計模式裏，建造者模式你可能聽起來有點陌生，可是一提到Builder模式，你可能就會稍微有點印象。這 個印象可能並非來源於你曾經寫過Builder模式。而是在日常編程的時候，總會碰到一個 xxx.Builder() 類。 這個Builder類就是咱們常常在無心中用到的Builder模式，也成爲建造者模式。git
2.常見的Builder模式
咱們總會在無心中用到一些Builder模式，你可能如今想不起來，那麼我能夠舉幾個例子稍微提醒一下你！github
- Retrofit (這裏面有的參數是我本身封裝的類。你只需知道，Retofit的構建是經過，自身的Builder類來構造的就行)
- OkHttpClient
- AlertDialog
3.Builder模式實例
- OkHttpClient源碼
這下是否是有了點印象。若是你稍加追究就會發現，不管是 Retrofit ，仍是 OkHttpClient 亦或是 AlertDialog ，他們都有一個共同的特色。就是都有一個Builder類。看到這你可能在想，這不是廢話嘛。哈哈的確是廢話，不過這幾個都有一個共同的特色就是，他們的構造方法都不是 public 修飾的而是 protect 修飾的。而惟一可以構造返回他們自己對象的就是他們各自 Builder類 重的 build() 或者 create() 方法。而我說的是否正確呢。下面分別上圖或者源碼證實一下！編程
/**
* OkHttpClient源碼
*/
public class OkHttpClient implements Cloneable, Call.Factory, WebSocket.Factory {
final int connectTimeout;
final int readTimeout;
final int writeTimeout;
final int pingInterval;
public OkHttpClient() {
this(new Builder());
}
OkHttpClient(Builder builder) {
this.connectTimeout = builder.connectTimeout;
this.readTimeout = builder.readTimeout;
this.writeTimeout = builder.writeTimeout;
this.pingInterval = builder.pingInterval;
}
//中間省略...
public static final class Builder {
int connectTimeout;
int readTimeout;
int writeTimeout;
int pingInterval;
public Builder() {
connectTimeout = 10_000;
readTimeout = 10_000;
writeTimeout = 10_000;
pingInterval = 0;
}
Builder(OkHttpClient okHttpClient) {
this.connectTimeout = okHttpClient.connectTimeout;
this.readTimeout = okHttpClient.readTimeout;
this.writeTimeout = okHttpClient.writeTimeout;
this.pingInterval = okHttpClient.pingInterval;
}
public Builder connectTimeout(long timeout, TimeUnit unit) {
connectTimeout = checkDuration("timeout", timeout, unit);
return this;
}
public Builder readTimeout(long timeout, TimeUnit unit) {
readTimeout = checkDuration("timeout", timeout, unit);
return this;
}
public Builder writeTimeout(long timeout, TimeUnit unit) {
writeTimeout = checkDuration("timeout", timeout, unit);
return this;
}
public Builder pingInterval(long interval, TimeUnit unit) {
pingInterval = checkDuration("interval", interval, unit);
return this;
}
public OkHttpClient build() {
return new OkHttpClient(this);
}
}
}
複製代碼
這裏我把OkHttpClient的源碼，縮減了一下，只留下了4個參數。讓咱們來看一下OkHttp框架是怎麼建立實例的。設計模式
- 他的構造方法是public。可是不能設置參數。一旦使用了
OkHttpClient okHttpClient=new OkHttpClient();
複製代碼
那麼它內部的參數，都是默認的，沒法經過okHttpClient這個實例來設置和修改參數。bash
- 咱們用OkHttpClient.Builder構建實例
OkHttpClient.Builder builder=new OkHttpClient.Builder();
OkHttpClient okHttpClient=builder
.readTimeout(5*1000, TimeUnit.SECONDS)
.writeTimeout(5*1000, TimeUnit.SECONDS)
.connectTimeout(5*1000, TimeUnit.SECONDS)
.build();
複製代碼
使用Builder建立實例的時候，不但能夠鏈式結構，還能夠修改參數 （緣由是由於，Builder類中的源碼，每一個方法的返回值都是Builder自己）框架
- Retrofit源碼
這裏咱們在舉一個Retrofit的例子 (代碼也會稍微簡化)函數
public final class Retrofit {
private final Map<Method, ServiceMethod<?, ?>> serviceMethodCache = new ConcurrentHashMap<>();
final okhttp3.Call.Factory callFactory;
final HttpUrl baseUrl;
final List<Converter.Factory> converterFactories;
final List<CallAdapter.Factory> adapterFactories;
final @Nullable Executor callbackExecutor;
final boolean validateEagerly;
Retrofit(okhttp3.Call.Factory callFactory, HttpUrl baseUrl,
List<Converter.Factory> converterFactories, List<CallAdapter.Factory> adapterFactories,
@Nullable Executor callbackExecutor, boolean validateEagerly) {
this.callFactory = callFactory;
this.baseUrl = baseUrl;
this.converterFactories = unmodifiableList(converterFactories); // Defensive copy at call site.
this.adapterFactories = unmodifiableList(adapterFactories); // Defensive copy at call site.
this.callbackExecutor = callbackExecutor;
this.validateEagerly = validateEagerly;
}
public Builder newBuilder() {
return new Builder(this);
}
public static final class Builder {
private final Platform platform;
private @Nullable okhttp3.Call.Factory callFactory;
private HttpUrl baseUrl;
private final List<Converter.Factory> converterFactories = new ArrayList<>();
private final List<CallAdapter.Factory> adapterFactories = new ArrayList<>();
private @Nullable Executor callbackExecutor;
private boolean validateEagerly;
Builder(Platform platform) {
this.platform = platform;
converterFactories.add(new BuiltInConverters());
}
public Builder() {
this(Platform.get());
}
Builder(Retrofit retrofit) {
platform = Platform.get();
callFactory = retrofit.callFactory;
baseUrl = retrofit.baseUrl;
converterFactories.addAll(retrofit.converterFactories);
adapterFactories.addAll(retrofit.adapterFactories);
// Remove the default, platform-aware call adapter added by build().
adapterFactories.remove(adapterFactories.size() - 1);
callbackExecutor = retrofit.callbackExecutor;
validateEagerly = retrofit.validateEagerly;
}
public Builder client(OkHttpClient client) {
return callFactory(checkNotNull(client, "client == null"));
}
public Builder callFactory(okhttp3.Call.Factory factory) {
this.callFactory = checkNotNull(factory, "factory == null");
return this;
}
public Builder baseUrl(String baseUrl) {
checkNotNull(baseUrl, "baseUrl == null");
HttpUrl httpUrl = HttpUrl.parse(baseUrl);
if (httpUrl == null) {
throw new IllegalArgumentException("Illegal URL: " + baseUrl);
}
return baseUrl(httpUrl);
}
public Builder baseUrl(HttpUrl baseUrl) {
checkNotNull(baseUrl, "baseUrl == null");
List<String> pathSegments = baseUrl.pathSegments();
if (!"".equals(pathSegments.get(pathSegments.size() - 1))) {
throw new IllegalArgumentException("baseUrl must end in /: " + baseUrl);
}
this.baseUrl = baseUrl;
return this;
}
public Builder addConverterFactory(Converter.Factory factory) {
converterFactories.add(checkNotNull(factory, "factory == null"));
return this;
}
public Builder addCallAdapterFactory(CallAdapter.Factory factory) {
adapterFactories.add(checkNotNull(factory, "factory == null"));
return this;
}
public Builder callbackExecutor(Executor executor) {
this.callbackExecutor = checkNotNull(executor, "executor == null");
return this;
}
public Builder validateEagerly(boolean validateEagerly) {
this.validateEagerly = validateEagerly;
return this;
}
public Retrofit build() {
if (baseUrl == null) {
throw new IllegalStateException("Base URL required.");
}
okhttp3.Call.Factory callFactory = this.callFactory;
if (callFactory == null) {
callFactory = new OkHttpClient();
}
Executor callbackExecutor = this.callbackExecutor;
if (callbackExecutor == null) {
callbackExecutor = platform.defaultCallbackExecutor();
}
// Make a defensive copy of the adapters and add the default Call adapter.
List<CallAdapter.Factory> adapterFactories = new ArrayList<>(this.adapterFactories);
adapterFactories.add(platform.defaultCallAdapterFactory(callbackExecutor));
// Make a defensive copy of the converters.
List<Converter.Factory> converterFactories = new ArrayList<>(this.converterFactories);
return new Retrofit(callFactory, baseUrl, converterFactories, adapterFactories,
callbackExecutor, validateEagerly);
}
}
}
複製代碼
上面是Retrofit源碼，Retrofit和OkHttp的區別就是，構造方法不是public的，不能直接new出來，只能經過 Builder.build()； 返回一個Retrofit實例。post
- AlertDialog就不舉例了，有興趣的能夠本身看下源碼。
4.什麼是Builder模式
- 定義：將一個複雜對象的構建與表示相分離，使得一樣的構建過程能夠建立不一樣的表示。大白話就是，你不須要知道這個類的內部是什麼樣的，只用把想使用的參數傳進去就能夠了，達到了解耦的目的。
- UML圖：下圖是一個GOF的傳統的Builder模式的圖例。由四部分組成1.Director,2.AbstractBuilder(抽象建造者),3.ConcreteBuilder(具體建造者),4.Product(產品類)。其實這裏也能夠將Product，分爲AbstractProduct(抽象產品類),ConcreteProduct(具體產品類)。
- 使用場景： 相同的方法不一樣的執行順尋，產生不一樣的事件結果。 多個部件或零件均可以裝配到一個對象中，可是產生的運行結果又不相同時。 產品類特別複雜，或者產品類中的調用順序不一樣產生了不一樣的做用，這個時候使用Builder設計模式 初始化一個對象特別複雜，參數多，且不少參數都有默認值。
5.簡化：
其實仔細觀察以後就會發現。不管時Retrofit仍是OkHttp爲何都和傳統的Builder模式不同呢，沒有Director類，沒有抽象建造者類，也沒有具體建造者類。那是由於，在使用過程當中，這些庫的做者，包括AlertDialog的做者，谷歌的開發人員，都將這三個類簡化進了一個Builder類。因此說，咱們在使用用設計模式的時候不要太過死板。而應隨機應變，連Google的開發人員都是這樣的，咱們固然也能夠取其精華去其糟粕。ui
/**
* 做者:jtl
* 日期:Created in 2019/1/28 11:19
* 描述:Person類（Builder模式）
* 更改:
*/
public class Person {
private String name;
private int age;
private Person(Builder builder) {
this.name = builder.name;
this.age = builder.age;
}
public String getName() {
return name;
}
public int getAge() {
return age;
}
public Builder newBuilder() {
return new Builder(this);
}
public static class Builder {
private String name;
private int age;
public Builder() {
this.age = 0;
this.name = "";
}
Builder(Person person) {
this.name = person.name;
this.age = person.age;
}
public Builder setAge(int age) {
this.age = age;
return this;
}
public Builder setName(String name) {
this.name = name;
return this;
}
public Person create() {
return new Person(this);
}
}
}
複製代碼
這個是相似與Retrofit和OkHttp的Builder設計模式的一個簡化Person類。你們能夠仿照這個試一下。this
6.區別：
Builder設計模式，以前咱們可能沒有使用過，可是一些經典的第三方庫，卻都使用了，將對象的建立與表示相分離，用戶不用關心它的內在是什麼樣的。只須要知道傳給他什麼參數。在一些有不少參數的產品類中使用該模式，能夠避免咱們在構造函數中傳入大量的默認參數來賦值的尷尬好比：
private String name;//姓名
private int age;//年齡
private String height;//身高
private String weight;//體重
private String sex;//性別
private String address;//家庭住址
private String nation;//種族
private String grade;//年紀
private String clazz;//班級
public Person(String name, int age, String height, String weight, String sex, String address, String nation, String grade, String clazz) {
this.name = name;
this.age = age;
this.height = height;
this.weight = weight;
this.sex = sex;
this.address = address;
this.nation = nation;
this.grade = grade;
this.clazz = clazz;
}
複製代碼
而使用了Builder模式後，咱們不須要關心Person類內部作了什麼樣的操做。
/**
* 做者:jtl
* 日期:Created in 2019/1/28 11:19
* 描述:簡化的Builder模式
* 更改:
*/
public class Person {
private String name;//姓名
private int age;//年齡
private String height;//身高
private String weight;//體重
private String sex;//性別
private String address;//家庭住址
private String nation;//種族
private String grade;//年紀
private String clazz;//班級
// public Person(String name, int age, String height, String weight, String sex, String address, String nation, String grade, String clazz) {
// this.name = name;
// this.age = age;
// this.height = height;
// this.weight = weight;
// this.sex = sex;
// this.address = address;
// this.nation = nation;
// this.grade = grade;
// this.clazz = clazz;
// }
private Person(Builder builder) {
this.name = builder.name;
this.age = builder.age;
this.height = builder.height;
this.weight = builder.weight;
this.sex = builder.sex;
this.address = builder.address;
this.nation = builder.nation;
this.grade = builder.grade;
this.clazz = builder.clazz;
}
public String getName() {
return name;
}
public int getAge() {
return age;
}
public Builder newBuilder() {
return new Builder(this);
}
public static class Builder {
private String name;//姓名
private int age;//年齡
private String height;//身高
private String weight;//體重
private String sex;//性別
private String address;//家庭住址
private String nation;//種族
private String grade;//年紀
private String clazz;//班級
public Builder() {
this.age = 0;
this.name = "";
this.height="150cm";
this.weight="45kg";
this.sex="男";
this.address="";
this.nation="";
this.grade="一年級";
this.clazz="一班";
}
Builder(Person person) {
this.name = person.name;
this.age = person.age;
this.height = person.height;
this.weight = person.weight;
this.sex = person.sex;
this.address = person.address;
this.nation = person.nation;
this.grade = person.grade;
this.clazz = person.clazz;
}
public Builder setAge(int age) {
this.age = age;
return this;
}
public Builder setName(String name) {
this.name = name;
return this;
}
public Builder setHeight(String height) {
this.height = height;
return this;
}
public Builder setWeight(String weight) {
this.weight = weight;
return this;
}
public Builder setSex(String sex) {
this.sex = sex;
return this;
}
public Builder setAddress(String address) {
this.address = address;
return this;
}
public Builder setNation(String nation) {
this.nation = nation;
return this;
}
public Builder setGrade(String grade) {
this.grade = grade;
return this;
}
public Builder setClazz(String clazz) {
this.clazz = clazz;
return this;
}
public Person create() {
return new Person(this);
}
}
}
複製代碼
可能有的小夥伴們就要問了：爲何不直接給Person類當中的參數，一個set方法呢？這樣不就不用Builder模式了嘛。關於這個問題，我是這樣理解的，若是咱們給Person類每個參數都設置一個set方法，這樣會增長Person類的功能和職責。違反了單一原則，不利於後期的維護。
7.結束語：
好了，就說到這兒了。仍是那句老話，風裏雨裏我都在這裏等你。大家的關注和點贊是我寫做的最大動力。但願你們可以給我一點點的動力。動動您的小手。若是文章中有錯誤的地方，但願您及時指出，我好改正。讓咱們共同進步。別忘了關注和點贊。謝謝您了！！！ 另附GitHub源碼地址：https://github.com/13046434521/DesignPatterns
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相關文章
- 1. 單例模式，今天你用了嘛
- 2. 觀察者模式，今天你用了嘛
- 3. Java Builder 模式,你搞懂了麼?
- 4. 今天你多態了嗎?
- 5. 今天你《ZAO》了嗎？
- 6. 今天，你Window 2008了嗎?
- 7. 今天你進步了嗎？
- 8. 今天你培訓了嗎？
- 9. 今天，你用智能音箱了嗎？
- 10. 今天，你用心生活了嗎？