ibatis 3.0 Dynamic Sql 設計解析(並與2.x的差異)

前段時間ibatis3.0發佈出來了，迫不及待，將其源碼下載拜讀。相對ibatis 2.x來說，3.0已是完全改變。具體我就不在這細說，論壇中有一個帖子介紹了ibatis 3.0的新特徵及使用。

由於其他模塊的源碼我還未細讀，在這篇中，先來討論Dynamic Sql在ibatis 3.0中的實現並比較2.x對應模塊的設計。

寫在前頭的話：

其實如從設計模式應用角度去看待ibatis 3.0中Dynamic Sql的實現，這篇跟我的上篇(HtmlParser設計解析(1)-解析器模式)相同，都是使用Interpreter模式。

這篇權當Interpreter模式的另一個demo，認我們體會這些開源項目中設計模式的使用。學習都是從模仿開始的，讓我們吸收高人們的經驗，應用於我們實踐項目需求中。

從總結中提高：

一、對比2.x中與3.0的Sqlmap中dynamic sql配置

2.x:

Xml代碼

<select id="dynamicGetAccountList" parameterClass="Account" resultClass="Account">
select ACC_ID as id,
ACC_FIRST_NAME as firstName,
ACC_LAST_NAME as lastName,
ACC_EMAIL as emailAddress from ACCOUNT
<dynamic prepend="WHERE">
<isNotNull prepend="AND" property="emailAddress">
ACC_EMAIL = #emailAddress#
</isNotNull>
<isNotNull property="idList" prepend=" or ACC_ID in ">
<iterate property="idList" conjunction="," open="(" close=")" >
#id#
</iterate>
</isNotNull>
</dynamic>
</select>

<select id="dynamicGetAccountList" parameterClass="Account" resultClass="Account"> 
      select ACC_ID as id,
      ACC_FIRST_NAME as firstName,
      ACC_LAST_NAME as lastName,
      ACC_EMAIL as emailAddress from ACCOUNT
	  
	<dynamic prepend="WHERE">
	  <isNotNull prepend="AND" property="emailAddress">
        ACC_EMAIL = #emailAddress#
      </isNotNull>
      <isNotNull property="idList" prepend=" or ACC_ID in ">   
		<iterate property="idList" conjunction="," open="(" close=")" >   
			#id#  
		</iterate>   
	  </isNotNull>   
    </dynamic>
</select>

3.0:

Xml代碼

<select id="dynamicGetAccountList" parameterType="Account" resultType="Account">
select ACC_ID as id,
ACC_FIRST_NAME as firstName,
ACC_LAST_NAME as lastName,
ACC_EMAIL as emailAddress from ACCOUNT
<where>
<if test="emailAddress != null">ACC_EMAIL = #{emailAddress}</if>
<if test="idList != null">
or ACC_ID IN
<foreach item="id" index="index" open="(" close=")" separator="," collection="idList">
#{idList[${index}]}
</foreach>
</if>
</where>
</select>

<select id="dynamicGetAccountList" parameterType="Account" resultType="Account">
	  select ACC_ID as id,
	  ACC_FIRST_NAME as firstName,
	  ACC_LAST_NAME as lastName,
	  ACC_EMAIL as emailAddress from ACCOUNT

	<where>
		<if test="emailAddress != null">ACC_EMAIL = #{emailAddress}</if>
		<if test="idList != null">
			or ACC_ID IN
			<foreach item="id" index="index" open="(" close=")" separator="," collection="idList">
				#{idList[${index}]}
			</foreach>
	   </if>
	</where>
</select>

從上面這個簡單的比較中，第一感覺3.0了中其dynamic sql更加簡潔明瞭。

其二，test="emailAddress != null" 添加了OGNL的解釋支持，可以動態支持更多的判斷，這將不限於原2.x中提供

的判斷邏輯，更不需要爲每個判斷條件加個標籤進行配置。

例如：<if test="id > 10 && id < 20"> ACC_EMAIL = #{emailAddress}</if>

<if test="Account.emailAddress != null "> ACC_EMAIL = #{emailAddress}</if> ……

二、2.x Dynamic Sql的設計

2.1、2.x中dynamic流程。

這裏帖出，我先前在分析ibatis 2.3時畫的一個對dynamic sql的整體使用的時序圖，可能會顯得亂而複雜。

2.2、主要類設計

在這，我們只關注這幾個類：XMLSqlSource、DynamicSql、SqlTagHandler (具體類結構圖見後)

XMLSqlSource：相當於一個工廠類，其核心方法parseDynamicTags()，用於解析sql Tag，並判斷是否是動態SQL標籤。如果true，返回一個DynamicSql對象並創建多個SqlChildt對象添加至動態SQL列表中(addChild())；false，返回RawSql對象(簡單的SQL語句) 。

DynamicSql：核心的動態SQL類。其動態條件判斷邏輯，參數映射等都發生在這個類中。

SqlTagHandle：動態條件判斷接口，其每個動態SQL標籤對應其一個子類。

接下來，我們具體看下在DynamicSql類中核心方法。

DynamicSql:

Java代碼

private void processBodyChildren(StatementScope statementScope, SqlTagContext ctx, Object parameterObject, Iterator localChildren, PrintWriter out) {
while (localChildren.hasNext()) { //XMLSqlSource 生成的動態SQL列表
SqlChild child = (SqlChild) localChildren.next();
if (child instanceof SqlText) {
... ... //組裝SQL語句及映射SQL參數
} else if (child instanceof SqlTag) {
SqlTag tag = (SqlTag) child;
SqlTagHandler handler = tag.getHandler(); //得到動態SQL標籤處理器
int response = SqlTagHandler.INCLUDE_BODY;
do {
response = handler.doStartFragment(ctx, tag, parameterObject); //處理開始片段
if (response != SqlTagHandler.SKIP_BODY) { //是否跳過，意思該判斷的條件爲false
processBodyChildren(statementScope, ctx, parameterObject, tag.getChildren(), pw); //遞歸處理
StringBuffer body = sw.getBuffer();
response = handler.doEndFragment(ctx, tag, parameterObject, body); //處理結束片段
handler.doPrepend(ctx, tag, parameterObject, body); //組裝SQL
}
} while (response == SqlTagHandler.REPEAT_BODY);
... ... }
}

private void processBodyChildren(StatementScope statementScope, SqlTagContext ctx, Object parameterObject, Iterator localChildren, PrintWriter out) {
    while (localChildren.hasNext()) { //XMLSqlSource 生成的動態SQL列表
      SqlChild child = (SqlChild) localChildren.next();
      if (child instanceof SqlText) {
          ... ... //組裝SQL語句及映射SQL參數
      } else if (child instanceof SqlTag) {
        SqlTag tag = (SqlTag) child;
        SqlTagHandler handler = tag.getHandler(); //得到動態SQL標籤處理器
        int response = SqlTagHandler.INCLUDE_BODY;
        do {          
          response = handler.doStartFragment(ctx, tag, parameterObject); //處理開始片段
          if (response != SqlTagHandler.SKIP_BODY) { //是否跳過，意思該判斷的條件爲false
            processBodyChildren(statementScope, ctx, parameterObject, tag.getChildren(), pw); //遞歸處理
            StringBuffer body = sw.getBuffer();
            response = handler.doEndFragment(ctx, tag, parameterObject, body); //處理結束片段
            handler.doPrepend(ctx, tag, parameterObject, body); //組裝SQL
            
          }
        } while (response == SqlTagHandler.REPEAT_BODY);
		... ...    }
}

2.3、SqlTagHandle設計

首先看下SqlTagHandle處理類的結果圖：

ConditionalTagHandler：

Java代碼

public abstract class ConditionalTagHandler extends BaseTagHandler {
... ...
public abstract boolean isCondition(SqlTagContext ctx, SqlTag tag, Object parameterObject);
public int doStartFragment(SqlTagContext ctx, SqlTag tag, Object parameterObject) {
ctx.pushRemoveFirstPrependMarker(tag);
if (isCondition(ctx, tag, parameterObject)) {
return SqlTagHandler.INCLUDE_BODY;
} else {
return SqlTagHandler.SKIP_BODY;
}
}
... ...
}

public abstract class ConditionalTagHandler extends BaseTagHandler {
  ... ...
  public abstract boolean isCondition(SqlTagContext ctx, SqlTag tag, Object parameterObject);

  public int doStartFragment(SqlTagContext ctx, SqlTag tag, Object parameterObject) {
    ctx.pushRemoveFirstPrependMarker(tag);
    if (isCondition(ctx, tag, parameterObject)) {
      return SqlTagHandler.INCLUDE_BODY;
    } else {
      return SqlTagHandler.SKIP_BODY;
    }
  }
  ... ...
}

IsNullTagHandler：

Java代碼

public class IsNullTagHandler extends ConditionalTagHandler {
private static final Probe PROBE = ProbeFactory.getProbe();
public boolean isCondition(SqlTagContext ctx, SqlTag tag, Object parameterObject) {
if (parameterObject == null) {
return true;
} else {
String prop = getResolvedProperty(ctx, tag);
Object value;
if (prop != null) {
value = PROBE.getObject(parameterObject, prop);
} else {
value = parameterObject;
}
return value == null;
}
}
}

public class IsNullTagHandler extends ConditionalTagHandler {
	private static final Probe PROBE = ProbeFactory.getProbe();
	public boolean isCondition(SqlTagContext ctx, SqlTag tag, Object parameterObject) {
		if (parameterObject == null) {
			return true;
		} else {
			String prop = getResolvedProperty(ctx, tag);
			Object value;
			if (prop != null) {
				value = PROBE.getObject(parameterObject, prop);
			} else {
				value = parameterObject;
			}
			return value == null;
		}
	}
}

至於其他的相關類，不在這列出了，有興趣的可以找其源碼瞭解下。

2.4、總結ibatis 2.X Dynamic Sql 的設計

從上面的分析中，可以體會出作者的dynamic sql這模塊的設計思路。從裝載sqlmap.xml中各sql配置(時序圖中的1步)，通過工廠創建DynamicSql和RawSql(時序圖中的3步)，然後分發之不同的處理器。

在DynamicSql中則調用SqlTagHandle判斷其條件(時序圖中的10步)。而SqlTagHandle的設計使用策略者模式，讓其不同的子類來處理這個判斷邏輯。

通過一系列的加工，最終組裝一個Sql對象，將值set至MappedStatement(時序圖中的14步)中，然後MappedStatement對象執行executeQueryWithCallback查詢數據(時序圖中的17步)，這兒會調用先前組裝的Sql對象(時序圖中的19步)。至於這其中的細節已不在這篇的研究這內。

三、3.0 Dynamic Sql的設計

至於3.0其基本流程跟2.x是一樣的，從裝載 -> 參數映射 -> 執行SQL -> 返回結果。我們直接切入主題，分析是核心部分。先從一個簡單的Dynamic Sql的測試用例開始。

3.1、測試用例

dynamic sql test:

Java代碼

@Test
public void shouldTrimWHEREInsteadOfORForSecondCondition() throws Exception {
/* SELECT * FROM BLOG
<where>
<if test="id != false"> and ID = #{id} </if>
<if test="name != false"> or NAME = #{name} </if>
</where>
*/
final String expected = "SELECT * FROM BLOG WHERE NAME = ?";
DynamicSqlSource source = createDynamicSqlSource(
new TextSqlNode("SELECT * FROM BLOG"),
new WhereSqlNode(mixedContents(
new IfSqlNode(
mixedContents(new TextSqlNode(" and ID = ? ")),"false"), new IfSqlNode(mixedContents(new TextSqlNode(" or NAME = ? ")), "true"))));
BoundSql boundSql = source.getBoundSql(null);
assertEquals(expected, boundSql.getSql());
}
private DynamicSqlSource createDynamicSqlSource(SqlNode... contents)
throws IOException, SQLException {
createBlogDataSource();
final String resource = ".../MapperConfig.xml";
final Reader reader = Resources.getResourceAsReader(resource);
SqlSessionFactory sqlMapper = new SqlSessionFactoryBuilder()
.build(reader);
Configuration configuration = sqlMapper.getConfiguration();
MixedSqlNode sqlNode = mixedContents(contents);
return new DynamicSqlSource(configuration, sqlNode);
}
private MixedSqlNode mixedContents(SqlNode... contents) {
return new MixedSqlNode(Arrays.asList(contents));
}

	@Test
	public void shouldTrimWHEREInsteadOfORForSecondCondition() throws Exception {
	 /*	SELECT * FROM BLOG
		<where>
			<if test="id != false"> and ID = #{id} </if>
			<if test="name != false"> or NAME = #{name} </if>
		</where>
	   */
		final String expected = "SELECT * FROM BLOG WHERE  NAME = ?";
		DynamicSqlSource source = createDynamicSqlSource(
				new TextSqlNode("SELECT * FROM BLOG"), 
					new WhereSqlNode(mixedContents(
							new IfSqlNode(
									mixedContents(new TextSqlNode("   and ID = ?  ")),"false"), new IfSqlNode(mixedContents(new TextSqlNode("   or NAME = ?  ")), "true"))));
		BoundSql boundSql = source.getBoundSql(null);
		assertEquals(expected, boundSql.getSql());
	}

	private DynamicSqlSource createDynamicSqlSource(SqlNode... contents)
			throws IOException, SQLException {
		createBlogDataSource();
		final String resource =  ".../MapperConfig.xml";
		final Reader reader = Resources.getResourceAsReader(resource);
		SqlSessionFactory sqlMapper = new SqlSessionFactoryBuilder()
				.build(reader);
		Configuration configuration = sqlMapper.getConfiguration();
		MixedSqlNode sqlNode = mixedContents(contents);
		return new DynamicSqlSource(configuration, sqlNode);
	}

	private MixedSqlNode mixedContents(SqlNode... contents) {
		return new MixedSqlNode(Arrays.asList(contents));
	}

有經驗的人，我想一眼就能看出其3.0中的設計思想，從Test中可以看出，或者我上一篇介紹的HtmlParser NodeFilter。

YES，在ibatis 3.0 dynamic sql設計正是應用瞭解釋器模式，替換了原在這種需求下相對顯得笨拙的策略者模式。

下面具體看下類結構圖。

3.2、類結構圖

SqlNode Class Diagram:

SqlSource Class Diagram:

3.3、配置文件的解析

在這，我就順便提下ibatis解析組件對dynamic sql的解析方式，以代碼見分曉吧。

XMLStatementBuilder：

Java代碼

public void parseStatementNode(XNode context) {
... ...
List<SqlNode> contents = parseDynamicTags(context);
MixedSqlNode rootSqlNode = new MixedSqlNode(contents);//再次包裝dynamic sql處理鏈
SqlSource sqlSource = new DynamicSqlSource(configuration, rootSqlNode); //默認初始化DynamicSqlSource
... ...
builderAssistant.addMappedStatement(id, sqlSource, statementType,
sqlCommandType, fetchSize, timeout, parameterMap,
parameterTypeClass, resultMap, resultTypeClass,
resultSetTypeEnum, flushCache, useCache, keyGenerator,
keyProperty); //將解析的所有屬性構建成相應的對象存入全局的申明對象(MappedStatement)中，後面只傳遞該對象。
}
private List<SqlNode> parseDynamicTags(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));
String nodeName = child.getNode().getNodeName();
if (child.getNode().getNodeType() == Node.CDATA_SECTION_NODE
|| child.getNode().getNodeType() == Node.TEXT_NODE) {
String data = child.getStringBody("");
contents.add(new TextSqlNode(data));
} else {
NodeHandler handler = nodeHandlers.get(nodeName);
if (handler == null) {
throw new BuilderException("Unknown element <" + nodeName "> in SQL statement.");
}
handler.handleNode(child, contents);
}
}
return contents;
}
private Map<String, NodeHandler> nodeHandlers = new HashMap<String, NodeHandler>() {
{
put("where", new WhereHandler());
put("set", new SetHandler());
put("foreach", new ForEachHandler());
put("if", new IfHandler());
... ...
}
};
private interface NodeHandler {
void handleNode(XNode nodeToHandle, List<SqlNode> targetContents);
}
private class WhereHandler implements NodeHandler {
public void handleNode(XNode nodeToHandle, List<SqlNode> targetContents) {
List<SqlNode> contents = parseDynamicTags(nodeToHandle);// 遍歷
MixedSqlNode mixedSqlNode = new MixedSqlNode(contents);//對應測試用例中的mixedContents方法
WhereSqlNode where = new WhereSqlNode(mixedSqlNode);
targetContents.add(where);
}
}
private class IfHandler implements NodeHandler {
public void handleNode(XNode nodeToHandle, List<SqlNode> targetContents) {
List<SqlNode> contents = parseDynamicTags(nodeToHandle);//遍歷
MixedSqlNode mixedSqlNode = new MixedSqlNode(contents);
String test = nodeToHandle.getStringAttribute("test");
IfSqlNode ifSqlNode = new IfSqlNode(mixedSqlNode, test);//初始化對應的處理器
targetContents.add(ifSqlNode);//
}
} // 其他的Handle詳見ibatis源碼~

	public void parseStatementNode(XNode context) {
                ...  ...
		List<SqlNode> contents = parseDynamicTags(context);
		MixedSqlNode rootSqlNode = new MixedSqlNode(contents);//再次包裝dynamic sql處理鏈
		SqlSource sqlSource = new DynamicSqlSource(configuration, rootSqlNode); //默認初始化DynamicSqlSource
                ... ...
		builderAssistant.addMappedStatement(id, sqlSource, statementType,
				sqlCommandType, fetchSize, timeout, parameterMap,
				parameterTypeClass, resultMap, resultTypeClass,
				resultSetTypeEnum, flushCache, useCache, keyGenerator,
				keyProperty); //將解析的所有屬性構建成相應的對象存入全局的申明對象(MappedStatement)中，後面只傳遞該對象。
	}

	private List<SqlNode> parseDynamicTags(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));
			String nodeName = child.getNode().getNodeName();
			if (child.getNode().getNodeType() == Node.CDATA_SECTION_NODE
					|| child.getNode().getNodeType() == Node.TEXT_NODE) {
				String data = child.getStringBody("");
				contents.add(new TextSqlNode(data));
			} else {
				NodeHandler handler = nodeHandlers.get(nodeName);
				if (handler == null) {
					throw new BuilderException("Unknown element <" + nodeName "> in SQL statement.");
				}
				handler.handleNode(child, contents);
			}
		}
		return contents;
	}         
	private Map<String, NodeHandler> nodeHandlers = new HashMap<String, NodeHandler>() {
		{
			put("where", new WhereHandler());
			put("set", new SetHandler());
			put("foreach", new ForEachHandler());
			put("if", new IfHandler());
			... ...
		}
	};
	private interface NodeHandler {
		void handleNode(XNode nodeToHandle, List<SqlNode> targetContents);
	}
	private class WhereHandler implements NodeHandler {
		public void handleNode(XNode nodeToHandle, List<SqlNode> targetContents) {
			List<SqlNode> contents = parseDynamicTags(nodeToHandle);// 遍歷
			MixedSqlNode mixedSqlNode = new MixedSqlNode(contents);//對應測試用例中的mixedContents方法
			WhereSqlNode where = new WhereSqlNode(mixedSqlNode);
			targetContents.add(where);
		}
	}
	private class IfHandler implements NodeHandler {
		public void handleNode(XNode nodeToHandle, List<SqlNode> targetContents) {
			List<SqlNode> contents = parseDynamicTags(nodeToHandle);//遍歷
			MixedSqlNode mixedSqlNode = new MixedSqlNode(contents);
			String test = nodeToHandle.getStringAttribute("test");
			IfSqlNode ifSqlNode = new IfSqlNode(mixedSqlNode, test);//初始化對應的處理器
			targetContents.add(ifSqlNode);//
		}
	} // 其他的Handle詳見ibatis源碼~

上面是其解析代碼的一部分，我想從這幾行代碼中，可以看出作者的思想了(遍歷XML各節點，以節點名查找相應對應的處理器，分發之該處理器執行"業務分析" — 策略者模式，這樣在XML中定義了多少標籤，這裏就需要多少個類與之對應，但如果策略類太多，這種方式就顯得笨拙了)。

以下就是其核心類的一部分源碼，先看再說。

3.4、DynamicSqlSource(核心類)

Java代碼

public class DynamicSqlSource implements SqlSource {
public DynamicSqlSource(Configuration configuration, SqlNode rootSqlNode) {
this.configuration = configuration;
this.rootSqlNode = rootSqlNode;
}
public BoundSql getBoundSql(Object parameterObject) {
DynamicContext context = new DynamicContext(parameterObject);//組裝後的結果存儲類
rootSqlNode.apply(context);//調用SqlNode解釋sql,並組裝成完整的sql(SqlNode的客戶端調用就在這)
SqlSourceBuilder sqlSourceParser = new SqlSourceBuilder(configuration);
Class parameterType = parameterObject == null ? Object.class : parameterObject.getClass();
SqlSource sqlSource = sqlSourceParser.parse(context.getSql(), parameterType);
BoundSql boundSql = sqlSource.getBoundSql(parameterObject);
for (Map.Entry<String, Object> entry : context.getBindings().entrySet()) {
boundSql.setAdditionalParameter(entry.getKey(), entry.getValue());
}
return boundSql;
}
}

public class DynamicSqlSource implements SqlSource {
	public DynamicSqlSource(Configuration configuration, SqlNode rootSqlNode) {
		this.configuration = configuration;
		this.rootSqlNode = rootSqlNode;
	}
	public BoundSql getBoundSql(Object parameterObject) {
		DynamicContext context = new DynamicContext(parameterObject);//組裝後的結果存儲類
		rootSqlNode.apply(context);//調用SqlNode解釋sql,並組裝成完整的sql(SqlNode的客戶端調用就在這)
		SqlSourceBuilder sqlSourceParser = new SqlSourceBuilder(configuration);
		Class parameterType = parameterObject == null ? Object.class : parameterObject.getClass();
		SqlSource sqlSource = sqlSourceParser.parse(context.getSql(), parameterType);
		BoundSql boundSql = sqlSource.getBoundSql(parameterObject);
		for (Map.Entry<String, Object> entry : context.getBindings().entrySet()) {
			boundSql.setAdditionalParameter(entry.getKey(), entry.getValue());
		}
		return boundSql;
	}
}

3.5、SqlNode

Java代碼

public interface SqlNode {
public boolean apply(DynamicContext context);
}

public interface SqlNode {
	public boolean apply(DynamicContext context);
}

MixedSqlNode.class

Java代碼

public class MixedSqlNode implements SqlNode {
... ....
public boolean apply(DynamicContext context) {
//遍歷組裝的解析內容
for (SqlNode sqlNode : contents) {
// 轉發至相關解釋器處理
sqlNode.apply(context);
}
return true;
}
}

public class MixedSqlNode implements SqlNode {
        ... ....
	public boolean apply(DynamicContext context) {
		//遍歷組裝的解析內容
		for (SqlNode sqlNode : contents) { 
			// 轉發至相關解釋器處理
			sqlNode.apply(context); 
		}
		return true;
	}
}

IfSqlNode.class

Java代碼

public class IfSqlNode implements SqlNode {
... ...
public IfSqlNode(SqlNode contents, String test) {
this.test = test;
this.contents = contents;
this.evaluator = new ExpressionEvaluator();
}
public boolean apply(DynamicContext context) {
if (evaluator.evaluateBoolean(test, context.getBindings())) {//OGNL Expressions
contents.apply(context);
return true; //
}
return false;
}
}

public class IfSqlNode implements SqlNode {
       ... ...
	public IfSqlNode(SqlNode contents, String test) {
		this.test = test;
		this.contents = contents;
		this.evaluator = new ExpressionEvaluator();
	}

	public boolean apply(DynamicContext context) {
		if (evaluator.evaluateBoolean(test, context.getBindings())) {//OGNL Expressions
			contents.apply(context);
			return true; //
		}
		return false;
	}
}

TextSqlNode.class

Java代碼

public class TextSqlNode implements SqlNode {
private String text;
public TextSqlNode(String text) {
this.text = text;
}

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