夯实设计原则之合成复用原则
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理念:
尽量使用对象组合,而不是继承来达到复用的目的;
合成复用原则就是在一个新的对象里通过关联关系(包括组合关系和聚合关系)来使用一些已有的对象,使之成为新对象的一部分;新对象通过委派调用已有对象的方法达到复用功能的目的;简言之:复用时要尽量使用组合/聚合关系,少用继承;
案例:
这次小明已经完成了手上的工作,利用空闲时间来研究了一下MyBatis的源码;
阅读了DefaultSqlSessionFactory
源码,如下:
/**
* DefaultSqlSessionFactory实例与其configuration属性就是聚合关系实现
*/
public class DefaultSqlSessionFactory implements SqlSessionFactory {
private final Configuration configuration;
public DefaultSqlSessionFactory(Configuration configuration) {
this.configuration = configuration;
}
@Override
public SqlSession openSession() {
return openSessionFromDataSource(configuration.getDefaultExecutorType(), null, false);
}
// ......
}
DefaultSqlSession
源码,如下:
/**
* DefaultSqlSession实例与其configuration属性就是聚合关系实现
* DefaultSqlSession实例与其executor属性就是组合关系的实现
*/
public class DefaultSqlSession implements SqlSession {
private final Configuration configuration;
private final Executor executor;
private final boolean autoCommit;
private boolean dirty;
private List<Cursor<?>> cursorList;
public DefaultSqlSession(Configuration configuration, Executor executor, boolean autoCommit) {
this.configuration = configuration;
this.executor = executor;
this.dirty = false;
this.autoCommit = autoCommit;
}
public DefaultSqlSession(Configuration configuration, Executor executor) {
this(configuration, executor, false);
}
// ......
}
以及BaseExecutor
源码,如下:
/**
* BaseExecutor实例与其transaction属性就是组合关系的实现
*/
public abstract class BaseExecutor implements Executor {
private static final Log log = LogFactory.getLog(BaseExecutor.class);
protected Transaction transaction;
protected Executor wrapper;
protected ConcurrentLinkedQueue<DeferredLoad> deferredLoads;
protected PerpetualCache localCache;
protected PerpetualCache localOutputParameterCache;
protected Configuration configuration;
protected int queryStack;
private boolean closed;
protected BaseExecutor(Configuration configuration, Transaction transaction) {
this.transaction = transaction;
this.deferredLoads = new ConcurrentLinkedQueue<>();
this.localCache = new PerpetualCache("LocalCache");
this.localOutputParameterCache = new PerpetualCache("LocalOutputParameterCache");
this.closed = false;
this.configuration = configuration;
this.wrapper = this;
}
// ......
}
从这几个类中,发现了一个共同的特性:除了实现了定义行为的接口,然后与其他类的关系都是通过组合关系或者聚合关系来实现的,这就是合成复用原则的实现;
标签:Configuration,原则,复用,private,夯实,protected,executor,configuration,public 来源: https://blog.csdn.net/gu19930914/article/details/116991785