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Mybatis中SqlNode的组合模式

组合( Composite )模式就是把对象组合成树形结构,以表示“部分-整体”的层次结构,用户可以像处理一个简单对象一样来处理一个复杂对象,从而使得调用者无需了解复杂元素的内部结构。

组合模式中的角色有:

  • 抽象组件(容器):定义了树形结构中所有类的公共行为,例如add(),remove()等方法。
  • 树叶:最终实现类,没有子类。
  • 树枝:有子类的管理类,并通过管理方法调用其管理的子类的相关操作。
  • 调用者:通过容器接口操作整个树形结构。

具体组合模式的例子可以参考 设计模式整理

现在我们来说一下SqlNode是什么,来看这么一段配置文件

<select id="findByGameTypeCount" resultType="java.lang.Long">
   select count(*)
   from betdetails a inner join UserBetOrder b on a.orderId = b.id
   <where>
      <if test="gameType != null and gameType > 0">
         a.gameType = #{gameType} and
      </if>
      <if test="currDrawno != null">
         b.currentDrawno = #{currDrawno} and
      </if>
      <if test="orderId != null and orderId > 0">
         a.orderId = #{orderId} and
      </if>
      <if test="status != null and status >= 0">
         a.status = #{status} and
      </if>
      <if test="userId != null and userId > 0">
         b.userId = #{userId} and
      </if>
      <if test="start != null">
         a.createTime &gt;= #{start} and
      </if>
      <if test="end != null">
         a.createTime &lt;= #{end} and
      </if>
      1 = 1
   </where>
</select>
<insert id="insertBetdetailsByBatch" parameterType="java.util.List">
   insert into betdetails(id,orderId,actorIndex,createTime,ballIndex,ballValue,betAmount,rate1,rate2,rate3,gameType,status,betResult,awardAmount,ballName) values
   <foreach collection="list" item="item" index="index" separator=",">
      (#{item.id},#{item.orderId},#{item.actorIndex},#{item.createTime},#{item.ballIndex},#{item.ballValue},#{item.betAmount},#{item.rate1},#{item.rate2},#{item.rate3},#{item.gameType},#{item.status},#{item.betResult},#{item.awardAmount},#{item.ballName})
   </foreach>
</insert>

这其中的<if><where><foreach>节点就是SqlNode节点,SqlNode是一个接口,代表着组合模式中的容器。只要是有SqlNode,那就代表着一定是一个动态的SQL,里面就有可能会有参数#{}

public interface SqlNode {
  //SqlNode接口中定义的唯一方法,该方法会根据用户传入的实参,解析该SqlNode所记录的动态SQL节点,并调用DynamicContext.appendSql()方法将解析后的SQL片段追加到
  //DynamicContext.sqlBuilder中保存
  //当SQL节点下的所有SqlNode完成解析后,就可以从DynamicContext中获取一条动态生成的完整的SQL语句
  boolean apply(DynamicContext context);
}

我们先来看一下DynamicContext是什么,它的核心字段如下

private final ContextMap bindings; //参考上下文
//在SqlNode解析动态SQL时,会将解析后的SQL语句片段添加到该属性中保存,最终拼凑出一条完成的SQL语句
private final StringBuilder sqlBuilder = new StringBuilder();

ContextMap是一个内部类,继承于HashMap,重写了get方法

static class ContextMap extends HashMap<String, Object> {
  private static final long serialVersionUID = 2977601501966151582L;
  //将用户传入的参数封装成MetaObject对象(类实例中检查类的属性是否包含getter,setter方法)
  private MetaObject parameterMetaObject;
  public ContextMap(MetaObject parameterMetaObject) {
    this.parameterMetaObject = parameterMetaObject;
  }

  @Override
  public Object get(Object key) {
    String strKey = (String) key;
    //如果ContextMap中已经包含了该key,则直接返回
    if (super.containsKey(strKey)) {
      return super.get(strKey);
    }
    //如果不包含该key,从parameterMetaObject中查找对应属性
    if (parameterMetaObject != null) {
      // issue #61 do not modify the context when reading
      return parameterMetaObject.getValue(strKey);
    }

    return null;
  }
}
public void appendSql(String sql) {
  sqlBuilder.append(sql);
  sqlBuilder.append(" ");
}

SqlNode的实现类如下

其中MixedSqlNode是树枝,TextSqlNode是树叶….

我们先来看一下TextSqlNode,TextSqlNode表示的是包含${}占位符的动态SQL节点。它的接口实现方法如下

@Override
public boolean apply(DynamicContext context) {
  //将动态SQL(带${}占位符的SQL)解析成完成SQL语句的解析器,即将${}占位符替换成实际的变量值
  GenericTokenParser parser = createParser(new BindingTokenParser(context, injectionFilter));
  //将解析后的SQL片段添加到DynamicContext中
  context.appendSql(parser.parse(text));
  return true;
}

BindingTokenParser是TextNode中定义的内部类,继承了TokenHandler接口,它的主要作用是根据DynamicContext.bindings集合中的信息解析SQL语句节点中的${}占位符。

private DynamicContext context;
private Pattern injectionFilter; //需要匹配的正则表达式
@Override
public String handleToken(String content) {
  //获取用户提供的实参
  Object parameter = context.getBindings().get("_parameter");
  //如果实参为null
  if (parameter == null) {
    //将参考上下文的value key设为null
    context.getBindings().put("value", null);
    //如果实参是一个常用数据类型的类(Integer.class,String.class,Byte.class等等)
  } else if (SimpleTypeRegistry.isSimpleType(parameter.getClass())) {
    //将参考上下文的value key设为该实参
    context.getBindings().put("value", parameter);
  }
  //通过OGNL解析参考上下文的值
  Object value = OgnlCache.getValue(content, context.getBindings());
  String srtValue = (value == null ? "" : String.valueOf(value)); // issue #274 return "" instead of "null"
  //检测合法性
  checkInjection(srtValue);
  return srtValue;
}
private void checkInjection(String value) {
  if (injectionFilter != null && !injectionFilter.matcher(value).matches()) {
    throw new ScriptingException("Invalid input. Please conform to regex" + injectionFilter.pattern());
  }
}

在OgnlCache中,对原生的OGNL进行了封装。OGNL表达式的解析过程是比较耗时的,为了提高效率,OgnlCache中使用了expressionCashe字段(ConcurrentHashMap<String,Object>类型)对解析后的OGNL表达式进行缓存。为了说明OGNL,我们先来看一个例子

@Data
@ToString
public class User {
    private int id;
    private String name;
}
public class OGNLDemo {
    public void testOgnl1() throws OgnlException {
        OgnlContext context = new OgnlContext();
        context.put("cn","China");
        String value = (String) context.get("cn");
        System.out.println(value);

        User user = new User();
        user.setId(100);
        user.setName("Jack");
        context.put("user",user);
        Object u = context.get("user");
        System.out.println(u);
        Object ognl = Ognl.parseExpression("#user.id");
        Object value1 = Ognl.getValue(ognl,context,context.getRoot());
        System.out.println(value1);

        User user1 = new User();
        user1.setId(200);
        user1.setName("Mark");
        context.setRoot(user1);
        Object ognl1 = Ognl.parseExpression("id");
        Object value2 = Ognl.getValue(ognl1,context,context.getRoot());
        System.out.println(value2);

        Object ognl2 = Ognl.parseExpression("@@floor(10.9)");
        Object value3 = Ognl.getValue(ognl2, context, context.getRoot());
        System.out.println(value3);
    }

    public static void main(String[] args) throws OgnlException {
        OGNLDemo demo = new OGNLDemo();
        demo.testOgnl1();
    }
}

运行结果:

China
User(id=100, name=Jack)
100
200
10.0

private static final Map<String, Object> expressionCache = new ConcurrentHashMap<String, Object>();
public static Object getValue(String expression, Object root) {
  try {
    //创建OgnlContext对象
    Map<Object, OgnlClassResolver> context = Ognl.createDefaultContext(root, new OgnlClassResolver());
    //使用OGNL执行expression表达式
    return Ognl.getValue(parseExpression(expression), context, root);
  } catch (OgnlException e) {
    throw new BuilderException("Error evaluating expression '" + expression + "'. Cause: " + e, e);
  }
}
private static Object parseExpression(String expression) throws OgnlException {
  //查找缓存
  Object node = expressionCache.get(expression);
  if (node == null) {
    //解析表达式
    node = Ognl.parseExpression(expression);
    //将表达式的解析结果添加到缓存中
    expressionCache.put(expression, node);
  }
  return node;
}

StaticTextSqlNode很简单,就是直接返回SQL语句

public class StaticTextSqlNode implements SqlNode {
  private final String text;

  public StaticTextSqlNode(String text) {
    this.text = text;
  }

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

}

IfSqlNode是解析<if>节点,字段含义如下

//用于解析<if>节点的test表达式的值
private final ExpressionEvaluator evaluator;
//记录<if>节点中test表达式
private final String test;
//记录了<if>节点的子节点
private final SqlNode contents;

接口方法如下

@Override
public boolean apply(DynamicContext context) {
  //检测test属性中记录的表达式
  if (evaluator.evaluateBoolean(test, context.getBindings())) {
    //如果test表达式为true,则执行子节点的apply()方法
    contents.apply(context);
    return true; //返回test表达式的结果为true
  }
  return false; //返回test表达式的结果为false
}

在ExpressionEvaluator中

public boolean evaluateBoolean(String expression, Object parameterObject) {
  //用OGNL解析expression表达式
  Object value = OgnlCache.getValue(expression, parameterObject);
  //处理Boolean类型
  if (value instanceof Boolean) {
    return (Boolean) value;
  }
  //处理数字类型
  if (value instanceof Number) {
    return new BigDecimal(String.valueOf(value)).compareTo(BigDecimal.ZERO) != 0;
  }
  return value != null;
}

TrimSqlNode会根据子节点的解析结果,添加或删除响应的前缀或后缀,比如有这么一段配置

<insert id="insertNotNullBetdetails" parameterType="com.cloud.model.game.Betdetails">
   insert into betdetails
   <trim prefix="(" suffix=")" suffixOverrides=",">
      <if test="id != null">id,</if>
      <if test="orderId != null">orderId,</if>
      <if test="actorIndex != null">actorIndex,</if>
      <if test="ballIndex != null">ballIndex,</if>
      <if test="ballValue != null">ballValue,</if>
      <if test="betAmount != null">betAmount,</if>
      <if test="createTime != null">createTime,</if>
      <if test="rate1 != null">rate1,</if>
      <if test="rate2 != null">rate2,</if>
      <if test="rate3 != null">rate3,</if>
      <if test="gameType != null">gameType,</if>
      <if test="status != null">status,</if>
      <if test="betResult != null">betResult,</if>
      <if test="awardAmount != null">awardAmount,</if>
      <if test="ballName != null">ballName,</if>
   </trim>
   <trim prefix="values (" suffix=")" suffixOverrides=",">
      <if test="id != null">#{id},</if>
      <if test="orderId != null">#{orderId},</if>
      <if test="actorIndex != null">#{actorIndex},</if>
      <if test="createTime != null">#{createTime},</if>
      <if test="ballIndex != null">#{ballIndex},</if>
      <if test="ballValue != null">#{ballValue},</if>
      <if test="betAmount != null">#{betAmount},</if>
      <if test="rate1 != null">#{rate1},</if>
      <if test="rate2 != null">#{rate2},</if>
      <if test="rate3 != null">#{rate3},</if>
      <if test="gameType != null">#{gameType},</if>
      <if test="status != null">#{status},</if>
      <if test="betResult != null">#{betResult},</if>
      <if test="awardAmount != null">#{awardAmount},</if>
      <if test="ballName != null">#{ballName},</if>
   </trim>
</insert>

TrimSqlNode中字段含义如下

private final SqlNode contents; //该<trim>节点的子节点
private final String prefix; //记录了前缀字符串(为<trim>节点包裹的SQL语句添加的前缀)
private final String suffix; //记录了后缀字符串(为<trim>节点包裹的SQL语句添加的后缀)
//如果<trim>节点包裹的SQL语句是空语句,删除指定的前缀,如where
private final List<String> prefixesToOverride;
//如果<trim>节点包裹的SQL语句是空语句,删除指定的后缀,如逗号
private final List<String> suffixesToOverride;

它的接口方法如下

@Override
public boolean apply(DynamicContext context) {
  //创建FilteredDynamicContext对象,FilteredDynamicContext是TrimSqlNode的内部类,继承于DynamicContext
  FilteredDynamicContext filteredDynamicContext = new FilteredDynamicContext(context);
  //调用子节点的apply()方法进行解析,注意收集SQL语句的是filteredDynamicContext
  boolean result = contents.apply(filteredDynamicContext);
  //处理前缀和后缀
  filteredDynamicContext.applyAll();
  return result;
}

FilteredDynamicContext的字段属性含义如下

private DynamicContext delegate; //底层封装的DynamicContext对象
private boolean prefixApplied; //是否已经处理过前缀
private boolean suffixApplied; //是否已经处理过后缀
private StringBuilder sqlBuffer; //用于记录子节点解析后的结果

FilteredDynamicContext的applyAll()方法

public void applyAll() {
  //获取子节点解析后的结果,并全部转化为大写
  sqlBuffer = new StringBuilder(sqlBuffer.toString().trim());
  String trimmedUppercaseSql = sqlBuffer.toString().toUpperCase(Locale.ENGLISH);
  if (trimmedUppercaseSql.length() > 0) {
    //处理前缀
    applyPrefix(sqlBuffer, trimmedUppercaseSql);
    //处理后缀
    applySuffix(sqlBuffer, trimmedUppercaseSql);
  }
  //将解析后的结果SQL片段添加到DynamicContext的StringBuilder中
  delegate.appendSql(sqlBuffer.toString());
}
private void applyPrefix(StringBuilder sql, String trimmedUppercaseSql) {
  if (!prefixApplied) { //如果还没有处理过前缀
    prefixApplied = true; //更新为已处理
    if (prefixesToOverride != null) { //如果需要删除的前缀列表不为null
      //遍历该前缀列表
      for (String toRemove : prefixesToOverride) {
        //如果<trim>子节点收集上来的SQL语句以该前缀开头
        if (trimmedUppercaseSql.startsWith(toRemove)) {
          //从<trim>子节点收集上来的StringBuilder中删除该前端
          sql.delete(0, toRemove.trim().length());
          break;
        }
      }
    }
    //如果有前缀字符串(比如说"("),将前缀字符串插入StringBuilder最前端
    if (prefix != null) {
      sql.insert(0, " ");
      sql.insert(0, prefix);
    }
  }
}
private void applySuffix(StringBuilder sql, String trimmedUppercaseSql) {
  if (!suffixApplied) { //如果还没有处理过后缀
    suffixApplied = true; //更新为已处理后缀
    if (suffixesToOverride != null) { //如果需要处理的后缀列表不为null
      //遍历该后缀列表
      for (String toRemove : suffixesToOverride) {
        //如果从<trim>子节点收集上来的SQL语句以该后缀结尾
        if (trimmedUppercaseSql.endsWith(toRemove) || trimmedUppercaseSql.endsWith(toRemove.trim())) {
          //获取该后缀的起始位置
          int start = sql.length() - toRemove.trim().length();
          //获取该后缀的终止位置
          int end = sql.length();
          //从<trim>子节点收集上来的StringBuilder中删除该后端
          sql.delete(start, end);
          break;
        }
      }
    }
    //如果有后缀字符串(比如说")"),将前缀字符串拼接上StringBuilder最后端
    if (suffix != null) {
      sql.append(" ");
      sql.append(suffix);
    }
  }
}

WhereSqlNode和SetSqlNode都继承于TrimSqlNode,他们只是在TrimSqlNode的属性中指定了固定的标记。

public class WhereSqlNode extends TrimSqlNode {

  private static List<String> prefixList = Arrays.asList("AND ","OR ","AND\n", "OR\n", "AND\r", "OR\r", "AND\t", "OR\t");

  public WhereSqlNode(Configuration configuration, SqlNode contents) {
    super(configuration, contents, "WHERE", prefixList, null, null);
  }

}
public class SetSqlNode extends TrimSqlNode {

  private static List<String> suffixList = Arrays.asList(",");

  public SetSqlNode(Configuration configuration,SqlNode contents) {
    super(configuration, contents, "SET", null, null, suffixList);
  }

}

ForEachSqlNode,在动态SQL语句中,通常需要对一个集合进行迭代,Mybatis提供了<foreach>标签实现该功能。在使用<foreach>标签迭代集合时,不仅可以使用集合的元素和索引值,还可以在循环开始之前或结束之后添加指定的字符串,也允许在迭代过程中添加指定的分隔符。配置样例如下

<insert id="insertBetdetailsByBatch" parameterType="java.util.List">
   insert into betdetails(id,orderId,actorIndex,createTime,ballIndex,ballValue,betAmount,rate1,rate2,rate3,gameType,status,betResult,awardAmount,ballName) values
   <foreach collection="list" item="item" index="index" separator=",">
      (#{item.id},#{item.orderId},#{item.actorIndex},#{item.createTime},#{item.ballIndex},#{item.ballValue},#{item.betAmount},#{item.rate1},#{item.rate2},#{item.rate3},#{item.gameType},#{item.status},#{item.betResult},#{item.awardAmount},#{item.ballName})
   </foreach>
</insert>

ForEachSqlNode中各个字段含义如下:

private final ExpressionEvaluator evaluator;
private final String collectionExpression;
private final SqlNode contents;
private final String open;
private final String close;
private final String separator;
private final String item;
private final String index;
private final Configuration configuration;

未经允许不得转载:ITyet » Mybatis中SqlNode的组合模式

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