【再探】设计模式—抽象工厂及建造者模式

抽象工厂模式和建造者模式都属于创建型模式。两者都能创建对应的对象，而创建者模式更侧重于创建复杂对象，将对象的创建过程封装起来，让客户端不需要知道对象的内部细节。

1 抽象工厂模式

需求：

在使用工厂方法模式时，当增加新的产品类型时，需要创建对应的Factory类，这导致类的数量增加，让系统变得臃肿。
需要保证同风格下生成一致的组件。比如在写页面时，有dark及light模式，我们希望button、text等组件能在不同模式下保持一致的风格。抽象工厂模式介绍

1.1 抽象工厂模式介绍

为创建一组对象提供一组解决方案。与工厂模式相比，抽象工厂模式中的具体工厂不只是创建一种产品，而是创建一族产品。

public class Button {private final String color;public Button(String color) {this.color = color;}@Overridepublic String toString() {return getClass().getSimpleName() + "{" +"color='" + color + '\'' +'}';}
}public class Text {private final String color;public Text(String color) {this.color = color;}@Overridepublic String toString() {return getClass().getSimpleName() + "{" +"color='" + color + '\'' +'}';}
}public class DarkButton extends Button{public DarkButton(String color) {super(color);}
}public class DarkText extends Text{public DarkText(String color) {super(color);}
}public class LightButton extends Button{public LightButton(String color) {super(color);}
}public class LightText extends Text{public LightText(String color) {super(color);}
}

public interface ComponentsFactory {Button buildButton();Text buildText();}public class DarkComponentFactory implements ComponentsFactory{private final String color = "dark";@Overridepublic Button buildButton() {return new DarkButton(color);}@Overridepublic Text buildText() {return new DarkText(color);}}public class LightComponentFactory implements ComponentsFactory{private final String color = "light";@Overridepublic Button buildButton() {return new LightButton(color);}@Overridepublic Text buildText() {return new LightText(color);}
}

public class HtmlWeb {public static void main(String[] args) {ComponentsFactory componentsFactory = new DarkComponentFactory();System.out.println("-----------dark模式-----------");System.out.println(componentsFactory.buildButton());System.out.println(componentsFactory.buildText());System.out.println("-----------light模式-----------");componentsFactory = new LightComponentFactory();System.out.println(componentsFactory.buildButton());System.out.println(componentsFactory.buildText());}
}

1.1.1 优缺点

优点：

隔离类的实例化过程，使得客户端并不需要知道如何创建对象。
当不同产品族多个对象被设计成一起工作时，能保证客户端始终只使用同一个产品族的对象。
减少了工厂类的数量。
增加新的产品族方便，符合开闭原则。

缺点：

不符合单一职责原则，一个类创建了多个对象。
族群增加新的种类时，不符合开闭原则，需要修改全部的工厂类。

2 建造者模式

需求：

需要创建一个复杂的对象，隔离类的实例化过程，使得客户端不需要知道对象的内部细节。
创建对象时，对执行顺序有要求。

2.1 建造者模式介绍

将一个复杂对象的构建与它的表示分离，使得同样的构建过程，不同的构建顺序可以构建不同的表示。

图构建模式UML

Director 为指挥者，用来控制Buider 的执行顺序，在实际开发中，这个角色经常会被省略，它的功能集成到Builder上；而Builder中的builderPart方法的返回值为它本身，这样就可以链式调用了。

public class JdbcConnector {private JdbcConnection connection;public void initConnection(URI uri) {connection = new JdbcConnection(uri);}public JdbcPreparedStatement getPreparedStatement(String query) {if (connection == null) throw new RuntimeException("连接器还未初始化");return connection.getPreparedStatement(query);}public static class JdbcConnection {public JdbcConnection(URI uri){System.out.println(uri);}public JdbcPreparedStatement getPreparedStatement(String query) {return new JdbcPreparedStatement(query);}}public static class JdbcPreparedStatement {String query;public JdbcPreparedStatement(String query) {this.query = query;}public String getResult() {return this.query;}}}public class JdbcConnectorBuilder {private String scheme;private String host;private String port;private String database;private String username;private String password;public JdbcConnectorBuilder setScheme(String scheme) {this.scheme = scheme;return this;}public JdbcConnectorBuilder setHost(String host) {this.host = host;return this;}public JdbcConnectorBuilder setPort(String port) {this.port = port;return this;}public JdbcConnectorBuilder setDatabase(String database) {this.database = database;return this;}public JdbcConnectorBuilder setUsername(String username) {this.username = username;return this;}public JdbcConnectorBuilder setPassword(String password) {this.password = password;return this;}/*** 产品*/private JdbcConnector jdbcConnector = null;public JdbcConnectorBuilder() {jdbcConnector = new JdbcConnector();}public JdbcConnector build() {StringBuilder sb = new StringBuilder("jdbc:");sb.append(scheme == null ? "mysql" : scheme).append("://");if (host == null) throw new RuntimeException("host不能为空");sb.append(host);sb.append(":").append(port == null ? "3306" : port);if (database == null) throw new RuntimeException("数据库不能为空");sb.append("/").append(database);try {URI uri = new URI(sb.toString());if (username == null || password == null) throw new RuntimeException("账号或密码错误");jdbcConnector.initConnection(uri);} catch (URISyntaxException e) {throw new RuntimeException("连接失败，连接信息有误");}return jdbcConnector;}}public class JdbcConnectionTest {public static void main(String[] args) {JdbcConnectorBuilder builder = new JdbcConnectorBuilder();builder.setScheme("mysql").setHost("localhost").setPort("3307").setDatabase("my-database").setUsername("root").setPassword("123456");JdbcConnector jdbcConnector = builder.build();JdbcConnector.JdbcPreparedStatement statement = jdbcConnector.getPreparedStatement("select * from student");System.out.println(statement.getResult());}
}

JDK 中的StringBuilder及Apache httpclient 的 URIBuilder 应用了建造者模式。

自定义StringBuilder

public class CustomStringBuilder {public static void main(String[] args) {CustomStringBuilder customStringBuilder = new CustomStringBuilder("hello customStringBuilder");for (int i =0; i < 100; i++) {customStringBuilder.append("---建造者模式---").append(i + "");}System.out.println(customStringBuilder);}char[] value;int count = 0;public CustomStringBuilder(int capacity) {value = new char[capacity];}public CustomStringBuilder(String str) {this(str.length() + 16);append(str);}CustomStringBuilder append(String str) {if (str == null) {throw new RuntimeException("字符串不能为空");}ensureCapacity(count + str.length());str.getChars(0,str.length(),value,count);count += str.length();return this;}private void ensureCapacity(int minCapacity) {if (minCapacity >= value.length) {value = Arrays.copyOf(value,value.length << 1);}}@Overridepublic String toString() {return new String(value,0,count);}
}

自定义URIBuilder

public class CustomURIBuilder {public static void main(String[] args) throws URISyntaxException {CustomURIBuilder customURIBuilder = new CustomURIBuilder();customURIBuilder.setHost("localhost").setPort("8080").setEncodedPath("/userinfo");customURIBuilder.appendQueryParam("username","hmf");customURIBuilder.appendQueryParam("status","1");customURIBuilder.appendQueryParam("createDate","2024/04/20");URI uri = customURIBuilder.build();System.out.println(uri);}private String scheme;private String host;private String port;private String encodedPath;private List<NameValuePair> queryParams;public CustomURIBuilder setScheme(String scheme) {this.scheme = scheme;return this;}public CustomURIBuilder setHost(String host) {this.host = host;return this;}public CustomURIBuilder setPort(String port) {this.port = port;return this;}public CustomURIBuilder setEncodedPath(String encodedPath) {this.encodedPath = encodedPath;return this;}public CustomURIBuilder appendQueryParam(String name,String value) {if (queryParams == null) queryParams = new ArrayList<>();queryParams.add(new NameValuePair(name,value));return this;}public URI build() throws URISyntaxException {return new URI(buildStr());}public String buildStr() {StringBuilder sb = new StringBuilder();if (this.scheme != null) sb.append(this.scheme).append("://");if (this.host == null) throw new RuntimeException("host不能为空");sb.append(this.host);if (this.port != null) sb.append(":").append(this.port);if (this.encodedPath != null) sb.append(this.encodedPath);if (this.queryParams != null) {for (int i = 0; i < this.queryParams.size(); i++) {sb.append(i == 0 ? "?" : "&").append(this.queryParams.get(i));}}return sb.toString();}private static class NameValuePair {String name;String value;public NameValuePair(String name, String value) {this.name = name;this.value = value;}@Overridepublic String toString() {if (this.value == null) return name;return name + "=" + value;}}}