Mybatis3源码分析(05)-加载Configuration-加载MappedStatement

MappedStatement说明

一个MappedStatement对象对应Mapper配置文件中的一个select/update/insert/delete节点，主要描述的是一条SQL语句。其属性有

//节点中的id属性加要命名空间
private String id;
//直接从节点属性中取
private Integer fetchSize;
//直接从节点属性中取
private Integer timeout;
private StatementType statementType;
private ResultSetType resultSetType;
//对应一条SQL语句
private SqlSource sqlSource;

//每条语句都对就一个缓存，如果有的话。
private Cache cache;
//这个已经过时了
private ParameterMap parameterMap;
private List<ResultMap> resultMaps;
private boolean flushCacheRequired;
private boolean useCache;
private boolean resultOrdered;
//SQL的类型,select/update/insert/detete
private SqlCommandType sqlCommandType;
private KeyGenerator keyGenerator;
private String[] keyProperties;
private String[] keyColumns;

//是否有内映射
private boolean hasNestedResultMaps;
private String databaseId;
private Log statementLog;
private LanguageDriver lang;
private String[] resultSets;

上面属性都比较简单，复杂的是SqlSource,下面有详细的描述！

XMLStatementBuilder.parseStatementNode()方法

resultMap元素的解析已经分析完毕。与resultMap不一样，XmlMapperBuilder在解析select/update/insert/delete的元素时会创建一个XMLStatementBuilder对象，解析的工作交由其方法parseStatementNode()方法完成。

private void buildStatementFromContext(List<XNode> list, String requiredDatabaseId) {
for (XNode context : list) {
//一个select/update/insert/delete元素创建一个XMLStatementBuilder对象
final XMLStatementBuilder statementParser = new XMLStatementBuilder(configuration, builderAssistant, context, requiredDatabaseId);
try {
//将元素解析成MappedStatemenet对象，并加入到Configuration中去
statementParser.parseStatementNode();
} catch (IncompleteElementException e) {
configuration.addIncompleteStatement(statementParser);
}
}

如下是parseStatementNode()方法的代码

public void parseStatementNode() {
String id = context.getStringAttribute("id");
String databaseId = context.getStringAttribute("databaseId");

if (!databaseIdMatchesCurrent(id, databaseId, this.requiredDatabaseId)) return;

Integer fetchSize = context.getIntAttribute("fetchSize");
Integer timeout = context.getIntAttribute("timeout");
String parameterMap = context.getStringAttribute("parameterMap");
String parameterType = context.getStringAttribute("parameterType");
Class<?> parameterTypeClass = resolveClass(parameterType);
String resultMap = context.getStringAttribute("resultMap");
String resultType = context.getStringAttribute("resultType");
String lang = context.getStringAttribute("lang");
LanguageDriver langDriver = getLanguageDriver(lang);

Class<?> resultTypeClass = resolveClass(resultType);
String resultSetType = context.getStringAttribute("resultSetType");
//Statement的类型，对应jdbc里的三个类型:Statement、PreparedStatement、CallableStatement，默认使用PreparedStatement
StatementType statementType = StatementType.valueOf(context.getStringAttribute("statementType", StatementType.PREPARED.toString()));
//这个也是跟jdbc里相对应的，一般采用默认即可
ResultSetType resultSetTypeEnum = resolveResultSetType(resultSetType);

//Sql的类型，select/update/insert/delete
String nodeName = context.getNode().getNodeName();
SqlCommandType sqlCommandType = SqlCommandType.valueOf(nodeName.toUpperCase(Locale.ENGLISH));
boolean isSelect = sqlCommandType == SqlCommandType.SELECT;
//是否刷新缓存
boolean flushCache = context.getBooleanAttribute("flushCache", !isSelect);
//是否使用缓存
boolean useCache = context.getBooleanAttribute("useCache", isSelect);
boolean resultOrdered = context.getBooleanAttribute("resultOrdered", false);

//不做分析
// Include Fragments before parsing
XMLIncludeTransformer includeParser = new XMLIncludeTransformer(configuration, builderAssistant);
includeParser.applyIncludes(context.getNode());
//不做分析
// Parse selectKey after includes and remove them.
processSelectKeyNodes(id, parameterTypeClass, langDriver);

//生成SqlSource对象，这个对象非常重要，接下来详细分析
// Parse the SQL (pre: <selectKey> and <include> were parsed and removed)
SqlSource sqlSource = langDriver.createSqlSource(configuration, context, parameterTypeClass);
String resultSets = context.getStringAttribute("resultSets");
String keyProperty = context.getStringAttribute("keyProperty");
String keyColumn = context.getStringAttribute("keyColumn");

//自动生成key，这里也不做讨论
KeyGenerator keyGenerator;
String keyStatementId = id + SelectKeyGenerator.SELECT_KEY_SUFFIX;
keyStatementId = builderAssistant.applyCurrentNamespace(keyStatementId, true);
if (configuration.hasKeyGenerator(keyStatementId)) {
keyGenerator = configuration.getKeyGenerator(keyStatementId);
} else {
keyGenerator = context.getBooleanAttribute("useGeneratedKeys",
configuration.isUseGeneratedKeys() && SqlCommandType.INSERT.equals(sqlCommandType))
? new Jdbc3KeyGenerator() : new NoKeyGenerator();
}
//生成MappedStatement对象，并加到Configuration中
builderAssistant.addMappedStatement(id, sqlSource, statementType, sqlCommandType,
fetchSize, timeout, parameterMap, parameterTypeClass, resultMap, resultTypeClass,
resultSetTypeEnum, flushCache, useCache, resultOrdered,
keyGenerator, keyProperty, keyColumn, databaseId, langDriver, resultSets);
}

上在方法里附件解析一些基本的属性外还有两个主要的部分

SqlSource的构建过程

SqlSource sqlSource = langDriver.createSqlSource(configuration, context, parameterTypeClass);

MappedStatement的构建过程

builderAssistant.addMappedStatement(id, sqlSource, statementType, sqlCommandType,
fetchSize, timeout, parameterMap, parameterTypeClass, resultMap, resultTypeClass,
resultSetTypeEnum, flushCache, useCache, resultOrdered,
keyGenerator, keyProperty, keyColumn, databaseId, langDriver, resultSets);

SqlSource构建过程

SqlSource接口

/**
* Represents the content of a mapped statement read from an XML file or an annotation.
* It creates the SQL that will be passed to the database out of the input parameter received from the user.
*
* @author Clinton Begin
*/
public interface SqlSource {

BoundSql getBoundSql(Object parameterObject);

}

SqlSource表示从mapper.xml或注解中读取的sql内容,该sql一般还不能都被直接执行,例如

<select id="selectUserDetail" resultMap="detailUserResultMap">
<!--CDATA里内容会都解析成一个SqlSource对象-->
<![CDATA[
select user_id,user_name,user_type,cust_id from tf_f_user a where a.user_id=#${userId}
]]>/select>

SqlSource只有一个方法:getBoundSql(paramenterObject),其中paramenterObject为运行sql里的实际参数

BoundSql

/**
* 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 {

private String sql;
private List<ParameterMapping> parameterMappings;
private Object parameterObject;
private Map<String, Object> additionalParameters;
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);
}
}

SqlBound代码并不多，就是一个普通的java对象，有两个属性非常重要

b5c2
sql:看代码里的注解，这个sql已经是经过了一些处理，可以被jdbc执行的了。xml里配置的sql可能有占位符#{username},这里的sql占位符已经被替换成"?"号了。
parameterMappings:执行sql对象的实际的参数。由此可以判断，每执行一条sql都会创建一个BoundSql对象。

SqlSource和BoundSql本身并不复杂，复杂的是这两个对象被创建的过程。

LanguageDriver

SqlSource对象是通过LanguageDriver对象构建的，在mapper.xml配置sql里可以通过lang属性指定一个LanguageDriver，但我们通常不会这样子做。当lang属性没有配置时，Mybatis会属性默认给一个。这个默认的LanguageDriver在Configuration的构造方法中定义的:

public Configuration() {
...
languageRegistry.setDefaultDriverClass(XMLLanguageDriver.class);
languageRegistry.register(RawLanguageDriver.class);
}

马上来看XMLLanguageDriver.createSqlSource()方法

public SqlSource createSqlSource(Configuration configuration, XNode script, Class<?> parameterType) {
XMLScriptBuilder builder = new XMLScriptBuilder(configuration, script, parameterType);
return builder.parseScriptNode();
}

XMLScriptBuilder

XMLScriptBuilder.parseScriptNode()方法

public SqlSource parseScriptNode() {
//将一个sql内容解析成多个SqlNode
List<SqlNode> contents = parseDynamicTags(context);
//将多个SqlNode组合一个SqlNode
MixedSqlNode rootSqlNode = new MixedSqlNode(contents);
SqlSource sqlSource = null;
//判断sql是否是动态的
if (isDynamic) {
//生成动态的SqlSource
sqlSource = new DynamicSqlSource(configuration, rootSqlNode);
} else {
//生成静态的SqlSource
sqlSource = new RawSqlSource(configuration, rootSqlNode, parameterType);
}
return sqlSource;
}

再看parseDynamicTagS(context)方法

private List<SqlNode> parseDynamicTags(XNode node) {
//一个sql会被解析成多个SqlNode，稍后会有示例详细说明
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));
if (child.getNode().getNodeType() == Node.CDATA_SECTION_NODE || child.getNode().getNodeType() == Node.TEXT_NODE) {
//如果这个Node只包含文本
String data = child.getStringBody("");
//生成一个TextSqlNode
TextSqlNode textSqlNode = new TextSqlNode(data);
//判断是否是动态的,如果文本里包含占位符，如#{username}或{table_name},isDynamic()方法就会返回true
if (textSqlNode.isDynamic()) {
contents.add(textSqlNode);
isDynamic = true;
} else {
contents.add(new StaticTextSqlNode(data));
}
} else if (child.getNode().getNodeType() == Node.ELEMENT_NODE) { // issue #628
//如果是有xml标签的Node,交由Handler处理，同时被认为是动态的
String nodeName = child.getNode().getNodeName();
NodeHandler handler = nodeHandlers.get(nodeName);
if (handler == null) {
throw new BuilderException("Unknown element <" + nodeName + "> in SQL statement.");
}
handler.handleNode(child, contents);

isDynamic = true;
}
}
return contents;
}

再看看nodeHandlers都有那些

private Map<String, NodeHandler> nodeHandlers = new HashMap<String, NodeHandler>() {
private static final long serialVersionUID = 7123056019193266281L;

{
//Mybatis3动态sql都支持那些配置，这里就很清楚啦
put("trim", new TrimHandler());
put("where", new WhereHandler());
put("set", new SetHandler());
put("foreach", new ForEachHandler());
put("if", new IfHandler());
put("choose", new ChooseHandler());
put("when", new IfHandler());
put("otherwise", new OtherwiseHandler());
put("bind", new BindHandler());
}
};

看到这里基本上能了解sql是怎么被解析的啦！举例说明:

<select id="selectUserDetail" resultMap="detailUserResultMap">
<![CDATA[
select user_id,user_name,user_type,cust_id --这里一行会解析成一个StaticTextSqlNode
from tf_f_user a --这里一行也会解析成一个StaticTextSqlNode
where a.user_id=#{userId} --这行会被解析成TextSqlNode,并且isDynamic被设置成true,因为有占位符
--这个空行也解析成一个StaticTextSqlNode
]]><!-- 这四个SqlNode会被组合成一个MixedSqlNode -->
</select>

再来个动态sql的:

<select id="selectUserDetail" resultMap="detailUserResultMap">
<![CDATA[
select user_id,user_name,user_type,cust_id --这里一行会解析成一个StaticTextSqlNode
from tf_f_user a --这里一行也会解析成一个StaticTextSqlNode
where a.user_id=#{userId} --这行会被解析成TextSqlNode,并且isDynamic被设置成true,因为有占位符
--这个空行也解析成一个StaticTextSqlNode
]]>
<if test="user_name!=null"> <!-- 这个标签里的内容会交给IfHandler处理 -->
and --这里的解析与上行的一样，解析成一个StaticTextSqlNode
user_name=#{userName} --这里的解析与上行的一样，也会被解析成一个TextSqlNode,并且isDynamic被设置成true,因为有占位符
</if><!-- IfHandler会将这里面的内个SqlNode组成MixedSqlNode再组成一个IfSqlNode -->
</select><!-- 这五个SqlNode会被组合成一个MixedSqlNode -->

附上IfHandler的代码

private class IfHandler implements NodeHandler {
public void handleNode(XNode nodeToHandle, List<SqlNode> targetContents) {
//解析子节点
List<SqlNode> contents = parseDynamicTags(nodeToHandle);
//组合
MixedSqlNode mixedSqlNode = new MixedSqlNode(contents);
String test = nodeToHandle.getStringAttribute("test");
//生成IfSqlNode
IfSqlNode ifSqlNode = new IfSqlNode(mixedSqlNode, test);
targetContents.add(ifSqlNode);
}
}

其他的nodeHandler在这里就不讨论了，实现方式与IfHandler差不多。如下两个方法也不在这里做讨论

SqlSource.getBoundSql()方法
SqlNode.apply(DynamicContextcontext)方法

因为这两个方法都是在sql被执行时才调用。在后续的SqlSession实现章节再讨论！