打造智能建筑商

构建API时，您应该始终考虑谁将使用它。当API简单易用时，用户就会感到满意。当用户满意时，每个人也都会满意。但是出色的可用性并非总是容易实现的。有一些模式对此有所帮助，在这篇文章中，我将重点介绍经典的构建器模式，以及如何使用步进构建器模式对其进行增强，以构建没有大脑接口，易于使用且不会出错的对象。因此，让我们开始绘制一些上下文，我们有2个域对象代表连接到某个远程或本地服务器的用户配置。当需要远程凭据时，在本地时。

package com.marco.sbp;
public class UserConfiguration {private final String name;private ServerDetails serverDetails;public UserConfiguration(String name) {this.name = name;}public void setServerDetails(ServerDetails serverDetails) {this.serverDetails = serverDetails;}public String getName() {return name;}public ServerDetails getServerDetails() {return serverDetails;}
}

package com.marco.sbp;
public class ServerDetails {private final String host;private String user;private String password;public ServerDetails(String host) {this.host = host;}public void setUser(String user) {this.user = user;}public void setPassword(String password) {this.password = password;}public String getHost() {return host;}public String getUser() {return user;}public String getPassword() {return password;}
}

我们希望使用两种不同的技术（经典的构建器模式和步骤构建器模式）来抽象上述对象的构造。

经典的构建器模式非常简单，它使用诸如onLocalHost，onRemoteHost等正确命名的方法来掩盖UserConfiguration和ServerDetails的创建。

package com.marco.sbp.builder;
import com.marco.sbp.ServerDetails;
import com.marco.sbp.UserConfiguration;
public class ClassicBuilder {private String name;private String host;private String user;private String password;public ClassicBuilder(String name){this.name = name;}public ClassicBuilder onLocalHost(){this.host = "localhost";return this;}public ClassicBuilder onRemoteHost(String remoteHost){this.host = remoteHost;return this;}public ClassicBuilder credentials(String user, String password){this.user = user;this.password = password;return this;}public UserConfiguration build(){UserConfiguration userConfiguration = new UserConfiguration(name);ServerDetails serverDetails = new ServerDetails(host);serverDetails.setUser(user);serverDetails.setPassword(password);                    userConfiguration.setServerDetails(serverDetails);return userConfiguration;}
}

步骤构建器模式仍在使用智能名称来构造对象，但是仅在需要使用接口和适当的封装时才公开这些方法。

package com.marco.sbp.builder;
import com.marco.sbp.ServerDetails;
import com.marco.sbp.UserConfiguration;/** "Step Builder" */
public class StepBuilder {public static NameStep newBuilder() {return new Steps();}private StepBuilder() {}public static interface NameStep {/*** @param name*            unique identifier for this User Configuration* @return ServerStep*/ServerStep name(String name);}       public static interface ServerStep {/*** The hostname of the server where the User Configuration file is stored will be set to "localhost".* * @return BuildStep*/public BuildStep onLocalhost();/*** The hostname of the server where the User Configuration file is stored.* * @return CredentialsStep*/public CredentialsStep onRemotehost(String host);}public static interface CredentialsStep {/*** Username required to connect to remote machine Password required to connect to remote machine* * @return BuildStep*/public BuildStep credentials(String user, String password);}public static interface BuildStep {/*** @return an instance of a UserConfiguration based on the parameters passed during the creation.*/public UserConfiguration build();}private static class Steps implements NameStep, ServerStep, CredentialsStep, BuildStep {private String name;private String host;private String user;private String password;public BuildStep onLocalhost() {this.host = "localhost";return this;}public ServerStep name(String name) {this.name = name;return null;}public CredentialsStep onRemotehost(String host) {this.host = host;return this;}public BuildStep credentials(String user, String password) {this.user = user;this.password = password;return this;}public UserConfiguration build() {UserConfiguration userConfiguration = new UserConfiguration(name);ServerDetails serverDetails = new ServerDetails(host);serverDetails.setUser(user);serverDetails.setPassword(password);                    userConfiguration.setServerDetails(serverDetails);return userConfiguration;}}
}

现在让我们看一下两个构建器的用户体验。经典构建器将使用用户配置的名称来构造，然后它将公开其所有方法，从而使用户过于自由，无法选择下一步。