建造者

  1. public class SqlSessionFactoryBuilder {
  3.   // 省略
  5.   public SqlSessionFactory build(Reader reader, String environment,
  6.                                  Properties properties) {
  7.     try {
  8.       XMLConfigBuilder parser = new XMLConfigBuilder(reader, 
  9.                                                      environment, properties);
  10.       return build(parser.parse());
  11.     } catch (Exception e) {
  12.       throw ExceptionFactory.wrapException("Error building SqlSession.", e);
  13.     } finally {
  14.       ErrorContext.instance().reset();
  15.       try {
  16.         reader.close();
  17.       } catch (IOException e) {
  18.         // Intentionally ignore. Prefer previous error.
  19.       }
  20.     }
  21.   }
  23.   public SqlSessionFactory build(InputStream inputStream) {
  24.     return build(inputStream, null, null);
  25.   }
  27.   public SqlSessionFactory build(InputStream inputStream, String environment) {
  28.     return build(inputStream, environment, null);
  29.   }
  31.  // 省略
  32. }

建造者设计模式作用：分离对象的属性与创建过程。mybatis 有大量的可配置属性，如果都需要用户去配置，框架的使用成本太高了。SqlSessionFactoryBuilder 对外隐藏了框架解析 xml 的细节，只使用必须的参数帮用户创建对象，如果没有配置的参数直接使用了默认值，降低了框架的使用成本。

模版

BaseExecutor

  1. public abstract class BaseExecutor implements Executor {
  3.   protected abstract int doUpdate(MappedStatement ms, Object parameter)
  4.       throws SQLException;
  6.   protected abstract List<BatchResult> doFlushStatements(boolean isRollback)
  7.       throws SQLException;
  9.   protected abstract <E> List<E> doQuery(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql)
  10.       throws SQLException;
  12.   protected abstract <E> Cursor<E> doQueryCursor(MappedStatement ms, Object parameter, RowBounds rowBounds, BoundSql boundSql)
  13.       throws SQLException;
  15. }

BaseExecutor 定义了很多方法的执行流程，具体的执行抽象出来交给子类去实现。

责任链

  1. public class InterceptorChain {
  3.   private final List<Interceptor> interceptors = new ArrayList<Interceptor>();
  5.   public Object pluginAll(Object target) {
  6.     for (Interceptor interceptor : interceptors) {
  7.       target = interceptor.plugin(target);
  8.     }
  9.     return target;
  10.   }
  12.   public void addInterceptor(Interceptor interceptor) {
  13.     interceptors.add(interceptor);
  14.   }
  16.   public List<Interceptor> getInterceptors() {
  17.     return Collections.unmodifiableList(interceptors);
  18.   }
  20. }

这里定义了一个拦截器链，用于mybatis插件扩展。mybais 插件可以在 sql 执行前后拦截做一些定制化的处理；

代理

  1. class PooledConnection implements InvocationHandler {  
  3. @Override
  4.   public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
  5.     String methodName = method.getName();
  6.     if (CLOSE.hashCode() == methodName.hashCode() && CLOSE.equals(methodName)) {
  7.       dataSource.pushConnection(this);
  8.       return null;
  9.     } else {
  10.       try {
  11.         if (!Object.class.equals(method.getDeclaringClass())) {
  12.           // issue #579 toString() should never fail
  13.           // throw an SQLException instead of a Runtime
  14.           checkConnection();
  15.         }
  16.         return method.invoke(realConnection, args);
  17.       } catch (Throwable t) {
  18.         throw ExceptionUtil.unwrapThrowable(t);
  19.       }
  20.     }
  21.   }
  23. }

装饰器

  1. public class CachingExecutor implements Executor {
  3.   private final Executor delegate;
  4.   private final TransactionalCacheManager tcm = new TransactionalCacheManager();
  6.   public CachingExecutor(Executor delegate) {
  7.     this.delegate = delegate;
  8.     delegate.setExecutorWrapper(this);
  9.   }
  10. }

此处装饰Executor，给 Executor 添加缓存功能。