设计模式课程 设计模式精讲 10-3 外观模式源码解析

1　　　　源码解析

1.1　　源码解析1（jdk中的JDBCUtils工具类）

1.2　　源码解析2（mybaties应用的Configuration）

1.3　　源码解析3（在tomcat(7.0.9版本或以上)中的应用）

 

1　　　　源码解析

1.1　　源码解析1（jdk中的JDBCUtils工具类）

jdbc在springJDBC中的封装

/**
     * Close the given JDBC Connection and ignore any thrown exception.
     * This is useful for typical finally blocks in manual JDBC code.
     * @param con the JDBC Connection to close (may be {@code null})
     */
    public static void closeConnection(Connection con) {
        if (con != null) {
            try {
                con.close();
            }
            catch (SQLException ex) {
                logger.debug("Could not close JDBC Connection", ex);
            }
            catch (Throwable ex) {
                // We don't trust the JDBC driver: It might throw RuntimeException or Error.
                logger.debug("Unexpected exception on closing JDBC Connection", ex);
            }
        }
    }

    /**
     * Close the given JDBC Statement and ignore any thrown exception.
     * This is useful for typical finally blocks in manual JDBC code.
     * @param stmt the JDBC Statement to close (may be {@code null})
     */
    public static void closeStatement(Statement stmt) {
        if (stmt != null) {
            try {
                stmt.close();
            }
            catch (SQLException ex) {
                logger.trace("Could not close JDBC Statement", ex);
            }
            catch (Throwable ex) {
                // We don't trust the JDBC driver: It might throw RuntimeException or Error.
                logger.trace("Unexpected exception on closing JDBC Statement", ex);
            }
        }
    }

    /**
     * Close the given JDBC ResultSet and ignore any thrown exception.
     * This is useful for typical finally blocks in manual JDBC code.
     * @param rs the JDBC ResultSet to close (may be {@code null})
     */
    public static void closeResultSet(ResultSet rs) {
        if (rs != null) {
            try {
                rs.close();
            }
            catch (SQLException ex) {
                logger.trace("Could not close JDBC ResultSet", ex);
            }
            catch (Throwable ex) {
                // We don't trust the JDBC driver: It might throw RuntimeException or Error.
                logger.trace("Unexpected exception on closing JDBC ResultSet", ex);
            }
        }
    }

1.2　　源码解析2（mybaties应用的Configuration）

通过封装之后，我们的客户端都有这些功能，这一组接口交给客户端来访问

public MetaObject newMetaObject(Object object) {
    return MetaObject.forObject(object, objectFactory, objectWrapperFactory, reflectorFactory);
  }

  public ParameterHandler newParameterHandler(MappedStatement mappedStatement, Object parameterObject, BoundSql boundSql) {
    ParameterHandler parameterHandler = mappedStatement.getLang().createParameterHandler(mappedStatement, parameterObject, boundSql);
    parameterHandler = (ParameterHandler) interceptorChain.pluginAll(parameterHandler);
    return parameterHandler;
  }

  public ResultSetHandler newResultSetHandler(Executor executor, MappedStatement mappedStatement, RowBounds rowBounds, ParameterHandler parameterHandler,
      ResultHandler resultHandler, BoundSql boundSql) {
    ResultSetHandler resultSetHandler = new DefaultResultSetHandler(executor, mappedStatement, parameterHandler, resultHandler, boundSql, rowBounds);
    resultSetHandler = (ResultSetHandler) interceptorChain.pluginAll(resultSetHandler);
    return resultSetHandler;
  }

1.3　　源码解析3（在tomcat(7.0.9版本或以上)中的应用）

request.java 和RequestFacade.java 都是HttpServletRequest  的子类，request.java声明RequestFacade，获取request的时候，实际返回的是RequestFacade的对象。我们看起来是使用了HTTPRequest的类，实际上我们使用的是RequestFacade这个外观类。

RequestFacade

@SuppressWarnings("deprecation")
public class RequestFacade implements HttpServletRequest {

    @Override
    public String getParameter(String name) {

        if (request == null) {
            throw new IllegalStateException(
                            sm.getString("requestFacade.nullRequest"));
        }

        if (Globals.IS_SECURITY_ENABLED){
            return AccessController.doPrivileged(
                new GetParameterPrivilegedAction(name));
        } else {
            return request.getParameter(name);
        }
    }

}

request.java

public class Request
implements HttpServletRequest {

/**
     * The facade associated with this request.
     */
    protected RequestFacade facade = null;


    /**
     * @return the <code>ServletRequest</code> for which this object
     * is the facade.  This method must be implemented by a subclass.
     */
    public HttpServletRequest getRequest() {
        if (facade == null) {
            facade = new RequestFacade(this);
        }
        return facade;
    }

}