Mybatis3源码分析(11)-Sql解析执行-BoundSql的加载-1

撸了今年阿里、腾讯和美团的面试,我有一个重要发现…….

作者:ashan_li

出处:https://blog.csdn.net/ashan_li/article/category/6047775/1?


整理完SqlSession和Executor的关系之后,接下来看看一条sql是怎么被解析执行的。

如下例:

    public static void queryUser(SqlSessionFactory sqlSessionFactory)
        {
            SqlSession sqlSession=sqlSessionFactory.openSession();
            try
            {
                Map<String,Object> param=new HashMap<>();
                param.put("userId", "21458594739");
                //sqlSession.selectList方法就是要详细分析的方法
                List<User> list=sqlSession.selectList("com.ashan.user.selectUserDetail", param);
                System.out.println(list);
                sqlSession.commit();
            }
            catch(Exception e)
            {
                sqlSession.rollback();
            }
            finally
            {
                sqlSession.close();
            }
        }

对应的配置文件:

    <resultMap type="com.ashan.mybatis.User" id="detailUserResultMap">
            <constructor>
                <idArg column="user_id" javaType="String"/>
                <arg column="user_name"/>
            </constructor>

            <result property="password" column="user_pwd" />
            <result property="type" column="user_type" javaType="com.ashan.mybatis.UserType"
                   typeHandler="com.ashan.mybatis.UserTypeHandler"/>
            <result property="svcnum" column="svc_num" />
            <association property="cust" javaType="com.ashan.mybatis.Cust">
                <id property="id" column="cust_id"/>
                <result property="custname" column="cust_name"/>
                <result property="certNo" column="cert_no"/>
            </association>

            <collection property="accts" ofType="com.ashan.mybatis.Acct">
                <id property="id" column="acct_id" />
                <result property="payName" column="pay_name"/>
                <result property="bankNo" column="bank_no"/>
            </collection>
        </resultMap>

        <select id="selectUserDetail" resultMap="detailUserResultMap">
            <![CDATA[
                select user_id,user_name,user_type,cust_id
                    from tf_f_user a
                    where a.user_id=#${userId}
            ]]>
        </select>

DefaultSqlSession.selectList方法

      public <E> List<E> selectList(String statement, Object parameter) {
        //RowBounds表示查询的范围,一般在分页时用到
        return this.selectList(statement, parameter, RowBounds.DEFAULT);
      }

      public <E> List<E> selectList(String statement, Object parameter, RowBounds rowBounds) {
        try {
          //从Configuration获取一个MappedStatement配置
          MappedStatement ms = configuration.getMappedStatement(statement);
          //直接调用executor.query()方法
          List<E> result = executor.query(ms, wrapCollection(parameter), rowBounds, Executor.NO_RESULT_HANDLER);
          return result;
        } catch (Exception e) {
          throw ExceptionFactory.wrapException("Error querying database.  Cause: " + e, e);
        } finally {
          ErrorContext.instance().reset();
        }
      }

从上可以看到sqlSession.selectList方法非常简单,他是用executor来完成查询的。再看看BaseExecutor对查询的实现:

    public <E> List<E> query(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler) throws SQLException {
        //获取一个BoundSql,这个BoundSql的获取过程就是本节要详细讨论的
        BoundSql boundSql = ms.getBoundSql(parameter);
        CacheKey key = createCacheKey(ms, parameter, rowBounds, boundSql);
        return query(ms, parameter, rowBounds, resultHandler, key, boundSql);
     }

BoundSql类定义

如下是BoundSql的源代码

    /**
     * An actual SQL String got form an {@link SqlSource} after having processed any dynamic content.
     * The SQL may have SQL placeholders "?" and an list (ordered) of an parameter mappings
     * with the additional information for each parameter (at least the property name of the input object to read
     * the value from).
     * </br>
     * Can also have additional parameters that are created by the dynamic language (for loops, bind...).
     */
    /**
     * @author Clinton Begin
     */
    public class BoundSql {
      //经过处理的sql,这个sql已经可以被数据库执行了
      private String sql;
      //sql中的参数映射,只是映射,没有包含实际的值
      private List<ParameterMapping> parameterMappings;
      //客户端执行sql时传入的参数
      private Object parameterObject;

      //暂时不讨论
      private Map<String, Object> additionalParameters;
      //暂时不讨论
      private MetaObject metaParameters;

      public BoundSql(Configuration configuration, String sql, List<ParameterMapping> parameterMappings, Object parameterObject) {
        this.sql = sql;
        this.parameterMappings = parameterMappings;
        this.parameterObject = parameterObject;
        this.additionalParameters = new HashMap<String, Object>();
        this.metaParameters = configuration.newMetaObject(additionalParameters);
      }

      public String getSql() {
        return sql;
      }

      public List<ParameterMapping> getParameterMappings() {
        return parameterMappings;
      }

      public Object getParameterObject() {
        return parameterObject;
      }

      public boolean hasAdditionalParameter(String name) {
        return metaParameters.hasGetter(name);
      }

      public void setAdditionalParameter(String name, Object value) {
        metaParameters.setValue(name, value);
      }

      public Object getAdditionalParameter(String name) {
        return metaParameters.getValue(name);
      }
    }

从源代码可以看出,BoundSql只是一个简单的java对象,有两个属性比较重要

  1. sql:从解析时可以看出这个sql不是配置文件中的sql,这个sql已经经过了处理(如:占用位符的处理、动态语句的解析if、foreach等待)
  2. parameterMappings:sql对应的参数列表

举例:

    <![CDATA[
                select user_id,user_name,user_type,cust_id
                    from tf_f_user a
                    where a.user_id=#{userId}
            ]]>
            <if test="userName!=null">
                and
                user_name=#{userName}
            </if>

如果执行这条sql里参数中的userName属性为空,那么sql的值将会是

    select user_id,user_name,user_type,cust_id
                    from tf_f_user a
                    where a.user_id=?

parameterMappings.size()大小为1,只记录了userId这个参数映射

如果userName不为空,那么sql的值将会是

    select user_id,user_name,user_type,cust_id
                    from tf_f_user a
                    where a.user_id=?
       and user_name=?

parameterMappings.size()大小为2,记录了userId和userName两个参数映射

MappedStatement.getBoundSql()方法

    public BoundSql getBoundSql(Object parameterObject) {
        //通过sqlSource对象获取
        BoundSql boundSql = sqlSource.getBoundSql(parameterObject);

        //parameterMap一般不会配置,如下内容不讨论
        List<ParameterMapping> parameterMappings = boundSql.getParameterMappings();
        if (parameterMappings == null || parameterMappings.size() <= 0) {
          boundSql = new BoundSql(configuration, boundSql.getSql(), parameterMap.getParameterMappings(), parameterObject);
        }

        // check for nested result maps in parameter mappings (issue #30)
        for (ParameterMapping pm : boundSql.getParameterMappings()) {
          String rmId = pm.getResultMapId();
          if (rmId != null) {
            ResultMap rm = configuration.getResultMap(rmId);
            if (rm != null) {
              hasNestedResultMaps |= rm.hasNestedResultMaps();
            }
          }
        }

        return boundSql;
      }

还记得sqlSource是怎么被创建的吗?(前面章节有详细说明)

    public SqlSource parseScriptNode() {
        List<SqlNode> contents = parseDynamicTags(context);
        MixedSqlNode rootSqlNode = new MixedSqlNode(contents);
        SqlSource sqlSource = null;
        if (isDynamic) {
          sqlSource = new DynamicSqlSource(configuration, rootSqlNode);
        } else {
          sqlSource = new RawSqlSource(configuration, rootSqlNode, parameterType);
        }
        return sqlSource;
      }

DynamicSqlSource.getBoundSql()方法

    public class DynamicSqlSource implements SqlSource {

      private Configuration configuration;
      private SqlNode rootSqlNode;

      public DynamicSqlSource(Configuration configuration, SqlNode rootSqlNode) {
        this.configuration = configuration;
        this.rootSqlNode = rootSqlNode;
      }

      public BoundSql getBoundSql(Object parameterObject) {
        DynamicContext context = new DynamicContext(configuration, parameterObject);
        //sqlNode使用组合模式实现,他有多个SqlNode对象
        //每个SqlNode的apply方法调用时,都为将sql加到context中,最终通过context.getSql()得到完整的sql
        rootSqlNode.apply(context);
        SqlSourceBuilder sqlSourceParser = new SqlSourceBuilder(configuration);
        Class<?> parameterType = parameterObject == null ? Object.class : parameterObject.getClass();
        SqlSource sqlSource = sqlSourceParser.parse(context.getSql(), parameterType, context.getBindings());
        BoundSql boundSql = sqlSource.getBoundSql(parameterObject);
        for (Map.Entry<String, Object> entry : context.getBindings().entrySet()) {
          boundSql.setAdditionalParameter(entry.getKey(), entry.getValue());
        }
        return boundSql;
      }

    }

DynamicContext可以看成是一个sql的容器,sqlNode的apply()方法会往这个容器上加sql.

DynamicContext动态上下文

这个类有两重要的属性

      //参数上下文,ContextMap为一个Map
      private final ContextMap bindings;
      //sql,sqlNode中的apply()方法调用了appendSql(text)方法,最终会将sql保存在这个属性中
      private final StringBuilder sqlBuilder = new StringBuilder();
       public void appendSql(String sql) {
        sqlBuilder.append(sql);
        sqlBuilder.append(" ");
      }

      public String getSql() {
        return sqlBuilder.toString().trim();
      }

再看看参数上下文

    static class ContextMap extends HashMap<String, Object> {
        private static final long serialVersionUID = 2977601501966151582L;
        //这个对运行时的参数进行了包装
        private MetaObject parameterMetaObject;
        public ContextMap(MetaObject parameterMetaObject) {
          this.parameterMetaObject = parameterMetaObject;
        }

        @Override
        public Object put(String key, Object value) {
          return super.put(key, value);
        }


        //这个方法才是最重要的
        @Override
        public Object get(Object key) {
          String strKey = (String) key;
          //如果自身的map里
          if (super.containsKey(strKey)) {
            return super.get(strKey);
          }

          if (parameterMetaObject != null) {
            //从参数里找
            Object object = parameterMetaObject.getValue(strKey);
            // issue #61 do not modify the context when reading
    //        if (object != null) {
    //          super.put(strKey, object);
    //        }

            return object;
          }

          return null;
        }

这里举两个例子来说明ContextMap,其中MetaObject将在下一章节详细讨论

  1. 参数为Map类型
        Map paraMap=new HashMap();
        paraMap.put("userId","12341234");
        paraMap.put("userName","ashan");
        List<User> list=sqlSession.selectList("dao.selectUser",paraMap);

  1. 参数为为一个普通的java对象

User user=new User(); user.setUserId("12341234"); user.setUserName("ashan"); List<User> list=sqlSession.selectList("dao.selectUser",user);

以上两种方式是最常见的参数设置方式,调用ContextMap.get(“userId”)方法之后,都能得到”12341234″!这就是ContextMap提供的功能。

SqlSource与SqlNode

下面详细分析apply()方法。

例如:DynamicSqlSource是从如下配置加载的

    <![CDATA[
                select user_id,user_name,user_type,cust_id
                    from tf_f_user a
                    where a.user_id=#{userId}
            ]]>
            <if test="userName!=null">
                and
                user_name=${userName}
            </if>

这个DynamicSqlSoure的结构如下(以上面的SQL为例),

2019080910011_1.png

结合例子说明一下sql在sqlNode中是怎么分布的

  1. StaticTextSqlNode1:保存了”select user_id,user_name,user_type,cust_id”
  2. StaticTextSqlNode2:保存了”from tf_f_user a”
  3. TextSqlNode3:保存了”where a.user_id=#{userId}”,同时标识为动态的,因为他有占位符
  4. StaticTextSqlNode4:保存了”and”
  5. TextSqlNode5:保存了”user_name=#{userName}”
  6. IfSqlNode:保存了其test属性值,StaticTextSqlNode4和TextSqlNode5是否加入的context中也是由其控制的

接下来看看每一种SqlNode是怎么解析sql并生成parameterMapping的

StaticTextSqlNode.apply()方法

     public boolean apply(DynamicContext context) {
        context.appendSql(text);
        return true;
      }

只是简单的把对应的test追加到context中。

所以StaticTextSqlNode1和StaticTextSqlNode2的apply方法执行后,DynamicContext中的sql内容为:

    select  user_id,user_name,user_type,cust_id from tf_f_user a

TextSqlNode.apply()方法

    public boolean apply(DynamicContext context) {
        //GenericTokenParser为一个占用符解析器
        //BindingTokenParsery为一个TohenHandler:解析具体的占位符
        GenericTokenParser parser = createParser(new BindingTokenParser(context));
        context.appendSql(parser.parse(text));
        return true;
      }
     private GenericTokenParser createParser(TokenHandler handler) {
        //解析${tab_name}这种占位符,注意不是这种#{propertyName}
        return new GenericTokenParser("${", "}", handler);
      }

再看看 GenericTokenParser.parse()方法:

    public String parse(String text) {
        StringBuilder builder = new StringBuilder();
        if (text != null && text.length() > 0) {
          char[] src = text.toCharArray();
          int offset = 0;
          int start = text.indexOf(openToken, offset);
          while (start > -1) {
            if (start > 0 && src[start - 1] == '\\') {
              // the variable is escaped. remove the backslash.
              builder.append(src, offset, start - 1).append(openToken);
              offset = start + openToken.length();
            } else {
              int end = text.indexOf(closeToken, start);
              if (end == -1) {
                builder.append(src, offset, src.length - offset);
                offset = src.length;
              } else {
                builder.append(src, offset, start - offset);
                offset = start + openToken.length();
                String content = new String(src, offset, end - offset);
                //关键是这句,调用了handler.handleToken()方法
                builder.append(handler.handleToken(content));
                offset = end + closeToken.length();
              }
            }
            start = text.indexOf(openToken, offset);
          }
          if (offset < src.length) {
            builder.append(src, offset, src.length - offset);
          }
        }
        return builder.toString();
      }

认真分析上面的代码,最关键的是调用了handler.handleToken(content)方法

如果text为:select ${primary_key},${col_name} from ${tab_name),那么handler.handleToken()方法会被调用三次,分别为:

  1. handler.handleToken(“primary_key”)
  2. handler.handleToken(“col_name”)
  3. handler.handleToken(“tab_name”)

再来看 BindingTokenParser.handleToken()方法

    public String handleToken(String content) {
          Object parameter = context.getBindings().get("_parameter");
          if (parameter == null) {
            context.getBindings().put("value", null);
          } else if (SimpleTypeRegistry.isSimpleType(parameter.getClass())) {
            context.getBindings().put("value", parameter);
          }
          //从ContextMap中取出content对应的值返回
          Object value = OgnlCache.getValue(content, context.getBindings());
          return (value == null ? "" : String.valueOf(value)); // issue #274 return "" instead of "null"
        }

从上面可以看到TextSqlNode.apply(),只会处理”${}”这种占位符,而不会处理这种占位符:”#{}”

所以当TextSqlNode3.apply()执行完成之后, DynamicContext中的sql内容为:

    select  user_id,user_name,user_type,cust_id from tf_f_user a where user_id=#{userId}

IfSqlNode.apply()方法

      public boolean apply(DynamicContext context) {
        //动态执行test属性中表达式,如果返回true,才会执行对应的SqlNode.apply()方法
        if (evaluator.evaluateBoolean(test, context.getBindings())) {
          contents.apply(context);
          return true;
        }
        return false;`
      }

结合上例,当IfSqlNode.apply()方法执行后,有两种情况:

如果参数中的userName不为空的话, DynamicContext中的sql内容为:

    select  user_id,user_name,user_type,cust_id from tf_f_user a where user_id=#{userId} and user_name=#{userName}

如果参数呻的userName为空的话, DynamicContext中的sql内容为:

    select  user_id,user_name,user_type,cust_id from tf_f_user a where user_id=#{userId}

ForEachSqlNode和ChooseSqlNode的实现原理跟IfSqlNode实现差不多,这里不做讨论!

小结

SqlNode.apply()方法生成的sql也只是半成品,并没有处理”#{}”占位符!这个占位符的处理后续再分析。

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