优化与扩展Mybatis的SqlMapper解析

public interface IStatementHandler {

    void handleStatementNode(Configuration configuration, SchemaSqlMapperParserDelegate delegate, XNode node);
}

//静态代码块，注册默认命名空间的StatementHandler
register("cache-ref", new CacheRefStatementHandler());
register("cache", new CacheStatementHandler());
register("parameterMap", new ParameterMapStatementHandler());
register("resultMap", new ResultMapStatementHandler());
register("sql", new SqlStatementHandler());
register("select|insert|update|delete", new CRUDStatementHandler());

public interface LanguageDriver {

  /**
   * 创建参数处理器*/
  ParameterHandler createParameterHandler(MappedStatement mappedStatement, Object parameterObject, BoundSql boundSql);

  /**
   * 根据XML节点创建SqlSource对象
   */
  SqlSource createSqlSource(Configuration configuration, XNode script, Class<?> parameterType);

  /**
   * 根据注解创建SQLSource对象 
   */
  SqlSource createSqlSource(Configuration configuration, String script, Class<?> parameterType);
}

public class SchemaXMLLanguageDriver extends XMLLanguageDriver {

    // 返回ExpressionParameterHandler，可以处理表达式的参数处理器
    @Override
    public ParameterHandler createParameterHandler(MappedStatement mappedStatement, Object parameterObject,
            BoundSql boundSql) {
        return SqlSessionComponetFactorys.newParameterHandler(mappedStatement, parameterObject, boundSql);
    }

    // 如果是DTD，则使用XMLScriptBuilder，否则使用SchemaXMLScriptBuilder，从而再次分开处理
    @Override
    public SqlSource createSqlSource(Configuration configuration, XNode script, Class<?> parameterType) {
        XMLScriptBuilder builder = SqlSessionComponetFactorys.newXMLScriptBuilder(configuration, script, parameterType);
        return builder.parseScriptNode();
    }
}

public interface IScriptHandler {

    void handleScriptNode(Configuration configuration, XNode node, List<SqlNode> targetContents);
}

//注册默认命名空间的ScriptHandler
register("trim", new TrimScriptHandler());
register("where", new WhereScriptHandler());
register("set", new SetScriptHandler());
register("foreach", new ForEachScriptHandler());
register("if|when", new IfScriptHandler());
register("choose", new ChooseScriptHandler());
//register("when", new IfScriptHandler());
register("otherwise", new OtherwiseScriptHandler());
register("bind", new BindScriptHandler());

public static List<SqlNode> parseDynamicTags(Configuration configuration, XNode node) {
    List<SqlNode> contents = new ArrayList<SqlNode>();
    NodeList children = node.getNode().getChildNodes();
    for (int i = 0; i < children.getLength(); i++) {
        XNode child = node.newXNode(children.item(i));
        short nodeType = child.getNode().getNodeType();
        if (nodeType == Node.CDATA_SECTION_NODE || nodeType == Node.TEXT_NODE) {
            String data = child.getStringBody("");
            data = decorate(configuration.getDatabaseId(), data);//对SQL文本进行装饰，从而嵌入SQL配置函数的处理
            ExpressionTextSqlNode expressionTextSqlNode = new ExpressionTextSqlNode(data);//使用表达式SQL文本，从而具有处理表达式的能力
            if (expressionTextSqlNode.isDynamic()) {
                contents.add(expressionTextSqlNode);
                setDynamic(true);
            } else {
                contents.add(new StaticTextSqlNode(data));
            }
        } else if (nodeType == Node.ELEMENT_NODE) { // issue
                                                                            // #628
            IScriptHandler handler = SchemaHandlers.getScriptHandler(child.getNode());//使用处理器机制，从而可以方便、自由地扩展
            if (handler == null) {
                throw new BuilderException("Unknown element <" + child.getNode().getNodeName() + "> in SQL statement.");
            }
            handler.handleScriptNode(configuration, child, contents);
            setDynamic(true);
        }
    }
    return contents;
}

public interface ISqlConfigFunction {
    
    /**
     * 优先级，如果有多个同名函数，使用order值小的
     * @return
     */
    public int getOrder();
    
    /**
     * 函数名称
     * @return
     */
    public String getName();
    
    /**
     * 执行SQL配置函数
     * @param databaseId 数据库ID
     * @param args       字符串参数
     * @return 
     */
    public String eval(String databaseId, String[] args);
}

public interface IExpressionHandler {
    
    public boolean isSupport(String expression, String databaseId);

    public Object eval(String expression, Object parameter, String databaseId);
}