文章目录
系列文章索引
MyBatis源码分析（一）MyBatis整体架构分析
MyBatis源码分析（二）SqlSessionFactory的构建及配置文件读取过程
MyBatis源码分析（二、续）SqlSource创建流程，SQL如何解析？如何将#{id}变成?的
MyBatis源码分析（三）SqlSession的执行主流程
MyBatis源码分析（四）插件拦截器的原理及使用
MyBatis源码分析（四、续）MyBatis分页插件拦截器设计与实现
MyBatis源码分析（五）一级缓存与二级缓存的原理
MyBatis源码分析（六）MetaObject工具类的使用与源码分析
MyBatis源码分析（七）MyBatis与Spring的整合原理与源码分析
深入理解JDK动态代理原理，使用javassist动手写一个动态代理框架
实例
此处我们分析的sql：
<select id="selectBlog" resultType="com.demo.Blog" useCache="true">
select * from blog where id = #{id}
</select>
一、SqlSource处理入口
在处理配置文件时，会处理Mapper.xml文件：
// org.apache.ibatis.builder.xml.XMLConfigBuilder#parseConfiguration
private void parseConfiguration(XNode root) {
try {
// issue #117 read properties first
propertiesElement(root.evalNode("properties"));
Properties settings = settingsAsProperties(root.evalNode("settings"));
loadCustomVfs(settings);
loadCustomLogImpl(settings);
typeAliasesElement(root.evalNode("typeAliases"));
pluginElement(root.evalNode("plugins"));
objectFactoryElement(root.evalNode("objectFactory"));
objectWrapperFactoryElement(root.evalNode("objectWrapperFactory"));
reflectorFactoryElement(root.evalNode("reflectorFactory"));
settingsElement(settings);
// read it after objectFactory and objectWrapperFactory issue #631
environmentsElement(root.evalNode("environments"));
databaseIdProviderElement(root.evalNode("databaseIdProvider"));
typeHandlerElement(root.evalNode("typeHandlers"));
mapperElement(root.evalNode("mappers")); // 处理mapper标签
} catch (Exception e) {
throw new BuilderException("Error parsing SQL Mapper Configuration. Cause: " + e, e);
}
}
// org.apache.ibatis.builder.xml.XMLConfigBuilder#mapperElement
private void mapperElement(XNode parent) throws Exception {
if (parent != null) {
for (XNode child : parent.getChildren()) {
if ("package".equals(child.getName())) {
String mapperPackage = child.getStringAttribute("name");
configuration.addMappers(mapperPackage);
} else {
String resource = child.getStringAttribute("resource");
String url = child.getStringAttribute("url");
String mapperClass = child.getStringAttribute("class");
if (resource != null && url == null && mapperClass == null) {
ErrorContext.instance().resource(resource);
try(InputStream inputStream = Resources.getResourceAsStream(resource)) {
XMLMapperBuilder mapperParser = new XMLMapperBuilder(inputStream, configuration, resource, configuration.getSqlFragments());
mapperParser.parse();
}
} else if (resource == null && url != null && mapperClass == null) {
ErrorContext.instance().resource(url);
try(InputStream inputStream = Resources.getUrlAsStream(url)){
XMLMapperBuilder mapperParser = new XMLMapperBuilder(inputStream, configuration, url, configuration.getSqlFragments());
mapperParser.parse(); // 解析Mapper.xml
}
} else if (resource == null && url == null && mapperClass != null) {
Class<?> mapperInterface = Resources.classForName(mapperClass);
configuration.addMapper(mapperInterface);
} else {
throw new BuilderException("A mapper element may only specify a url, resource or class, but not more than one.");
}
}
}
}
}
// org.apache.ibatis.builder.xml.XMLMapperBuilder#parse
public void parse() {
if (!configuration.isResourceLoaded(resource)) {
configurationElement(parser.evalNode("/mapper"));
configuration.addLoadedResource(resource);
bindMapperForNamespace();
}
parsePendingResultMaps();
parsePendingCacheRefs();
// 预处理Statement
parsePendingStatements();
}
// org.apache.ibatis.builder.xml.XMLMapperBuilder#parsePendingStatements
private void parsePendingStatements() {
Collection<XMLStatementBuilder> incompleteStatements = configuration.getIncompleteStatements();
synchronized (incompleteStatements) {
Iterator<XMLStatementBuilder> iter = incompleteStatements.iterator();
while (iter.hasNext()) {
try {
iter.next().parseStatementNode(); // 处理node
iter.remove();
} catch (IncompleteElementException e) {
// Statement is still missing a resource...
}
}
}
}
// org.apache.ibatis.builder.xml.XMLStatementBuilder#parseStatementNode
public void parseStatementNode() {
String id = context.getStringAttribute("id");
String databaseId = context.getStringAttribute("databaseId");
if (!databaseIdMatchesCurrent(id, databaseId, this.requiredDatabaseId)) {
return;
}
String nodeName = context.getNode().getNodeName();
SqlCommandType sqlCommandType = SqlCommandType.valueOf(nodeName.toUpperCase(Locale.ENGLISH));
boolean isSelect = sqlCommandType == SqlCommandType.SELECT;
boolean flushCache = context.getBooleanAttribute("flushCache", !isSelect);
boolean useCache = context.getBooleanAttribute("useCache", isSelect);
boolean resultOrdered = context.getBooleanAttribute("resultOrdered", false);
// Include Fragments before parsing
XMLIncludeTransformer includeParser = new XMLIncludeTransformer(configuration, builderAssistant);
includeParser.applyIncludes(context.getNode());
String parameterType = context.getStringAttribute("parameterType");
Class<?> parameterTypeClass = resolveClass(parameterType);
String lang = context.getStringAttribute("lang");
LanguageDriver langDriver = getLanguageDriver(lang);
// Parse selectKey after includes and remove them.
processSelectKeyNodes(id, parameterTypeClass, langDriver);
// Parse the SQL (pre: <selectKey> and <include> were parsed and removed)
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))
? Jdbc3KeyGenerator.INSTANCE : NoKeyGenerator.INSTANCE;
}
// 创建SqlSource核心逻辑
SqlSource sqlSource = langDriver.createSqlSource(configuration, context, parameterTypeClass);
StatementType statementType = StatementType.valueOf(context.getStringAttribute("statementType", StatementType.PREPARED.toString()));
Integer fetchSize = context.getIntAttribute("fetchSize");
Integer timeout = context.getIntAttribute("timeout");
String parameterMap = context.getStringAttribute("parameterMap");
String resultType = context.getStringAttribute("resultType");
Class<?> resultTypeClass = resolveClass(resultType);
String resultMap = context.getStringAttribute("resultMap");
String resultSetType = context.getStringAttribute("resultSetType");
ResultSetType resultSetTypeEnum = resolveResultSetType(resultSetType);
if (resultSetTypeEnum == null) {
resultSetTypeEnum = configuration.getDefaultResultSetType();
}
String keyProperty = context.getStringAttribute("keyProperty");
String keyColumn = context.getStringAttribute("keyColumn");
String resultSets = context.getStringAttribute("resultSets");
builderAssistant.addMappedStatement(id, sqlSource, statementType, sqlCommandType,
fetchSize, timeout, parameterMap, parameterTypeClass, resultMap, resultTypeClass,
resultSetTypeEnum, flushCache, useCache, resultOrdered,
keyGenerator, keyProperty, keyColumn, databaseId, langDriver, resultSets);
}
我们找到了处理SqlSource的核心入口。
二、SqlSource处理逻辑
创建SqlSource，解析SQL，封装SQL语句（未参数绑定）和入参信息。
// org.apache.ibatis.scripting.xmltags.XMLLanguageDriver#createSqlSource(org.apache.ibatis.session.Configuration, org.apache.ibatis.parsing.XNode, java.lang.Class<?>)
@Override
public SqlSource createSqlSource(Configuration configuration, XNode script, Class<?> parameterType) {
// 初始化了动态SQL标签处理器
XMLScriptBuilder builder = new XMLScriptBuilder(configuration, script, parameterType);
// 解析动态SQL
return builder.parseScriptNode();
}
1、XMLScriptBuilder 构造方法
public XMLScriptBuilder(Configuration configuration, XNode context, Class<?> parameterType) {
super(configuration);
this.context = context;
this.parameterType = parameterType;
// 初始化动态SQL中的节点处理器集合
initNodeHandlerMap();
}
// 动态sql所有的节点
private void initNodeHandlerMap() {
nodeHandlerMap.put("trim", new TrimHandler());
nodeHandlerMap.put("where", new WhereHandler());
nodeHandlerMap.put("set", new SetHandler());
nodeHandlerMap.put("foreach", new ForEachHandler());
nodeHandlerMap.put("if", new IfHandler());
nodeHandlerMap.put("choose", new ChooseHandler());
nodeHandlerMap.put("when", new IfHandler());
nodeHandlerMap.put("otherwise", new OtherwiseHandler());
nodeHandlerMap.put("bind", new BindHandler());
}
2、解析动态sql
XMLScriptBuilder#parseScriptNode用于解析动态sql：
public SqlSource parseScriptNode() {
// 解析select\insert\ update\delete标签中的SQL语句，最终将解析到的SqlNode封装到MixedSqlNode中的List集合中
// ****将带有${}号的SQL信息封装到TextSqlNode
// ****将带有#{}号的SQL信息封装到StaticTextSqlNode
// ****将动态SQL标签中的SQL信息分别封装到不同的SqlNode中
MixedSqlNode rootSqlNode = parseDynamicTags(context);
SqlSource sqlSource;
if (isDynamic) {
// 如果SQL中包含${}和动态SQL语句，则将SqlNode封装到DynamicSqlSource
// 最终结果是：select id from blog where id = ${id}
sqlSource = new DynamicSqlSource(configuration, rootSqlNode);
} else {
// 如果SQL中包含#{}，则将SqlNode封装到RawSqlSource中，并指定parameterType
// 最终的结果是：select id from blog where id = ?
sqlSource = new RawSqlSource(configuration, rootSqlNode, parameterType);
}
return sqlSource;
}
parseDynamicTags解析sql语句：
解析select\insert\ update\delete标签中的SQL语句，最终将解析到的SqlNode封装到MixedSqlNode中的List集合中。
// org.apache.ibatis.scripting.xmltags.XMLScriptBuilder#parseDynamicTags
protected MixedSqlNode parseDynamicTags(XNode node) {
List<SqlNode> contents = new ArrayList<>();
//获取<select>\<insert>\<update>\<delete>4个标签的子节点，子节点包括元素节点和文本节点
NodeList children = node.getNode().getChildNodes();
for (int i = 0; i < children.getLength(); i++) {
// 获取标签内的原始自定义sql：select * from blog where id = #{id}
XNode child = node.newXNode(children.item(i));
// 处理文本节点
if (child.getNode().getNodeType() == Node.CDATA_SECTION_NODE || child.getNode().getNodeType() == Node.TEXT_NODE) {
String data = child.getStringBody("");
// 将文本内容封装到SqlNode中，还是原始sql
TextSqlNode textSqlNode = new TextSqlNode(data);
// SQL语句中带有${}的话，就表示是dynamic的
if (textSqlNode.isDynamic()) {
contents.add(textSqlNode);
isDynamic = true;
} else {
// SQL语句中（除了${}和下面的动态SQL标签），就表示是static的
// StaticTextSqlNode的apply只是进行字符串的追加操作
contents.add(new StaticTextSqlNode(data));
}
//处理元素节点
} else if (child.getNode().getNodeType() == Node.ELEMENT_NODE) { // issue #628
String nodeName = child.getNode().getNodeName();
// 动态SQL标签处理器
// 策略模式
NodeHandler handler = nodeHandlerMap.get(nodeName);
if (handler == null) {
throw new BuilderException("Unknown element <" + nodeName + "> in SQL statement.");
}
handler.handleNode(child, contents);
// 动态SQL标签是dynamic的
isDynamic = true;
}
}
return new MixedSqlNode(contents);
}
最终返回了携带了原始sql的对象。
3、DynamicSqlSource
如果SQL中包含${}和动态SQL语句，则将SqlNode封装到DynamicSqlSource。
咱们此处研究的是简单的、包含#{id}的sql，暂不研究动态SQL。
select id from blog where id = ${id}
比如说以上sql，会原封不动的生成SqlSource，并不会进行解析。
4、RawSqlSource解析sql
如果SQL中包含#{}，则将SqlNode封装到RawSqlSource中，并指定parameterType
我们看一下RawSqlSource的构造方法：
public RawSqlSource(Configuration configuration, SqlNode rootSqlNode, Class<?> parameterType) {
this(configuration, getSql(configuration, rootSqlNode), parameterType);
}
public RawSqlSource(Configuration configuration, String sql, Class<?> parameterType) {
// 解析SQL语句
SqlSourceBuilder sqlSourceParser = new SqlSourceBuilder(configuration);
// 获取入参类型
Class<?> clazz = parameterType == null ? Object.class : parameterType;
// 开始解析
sqlSource = sqlSourceParser.parse(sql, clazz, new HashMap<>());
}
（1）parse方法解析sql
// org.apache.ibatis.builder.SqlSourceBuilder#parse
public SqlSource parse(String originalSql, Class<?> parameterType, Map<String, Object> additionalParameters) {
ParameterMappingTokenHandler handler = new ParameterMappingTokenHandler(configuration, parameterType, additionalParameters);
// 创建分词解析器
GenericTokenParser parser = new GenericTokenParser("#{", "}", handler);
String sql;
// 解析#{}
if (configuration.isShrinkWhitespacesInSql()) {
sql = parser.parse(removeExtraWhitespaces(originalSql)); // 处理额外的空格
} else {
sql = parser.parse(originalSql); // 解析，最终sql为select * from blog where id = ?
}
// 将解析之后的SQL信息，封装到StaticSqlSource对象中
// SQL字符串是带有?号的字符串，?相关的参数信息，封装到ParameterMapping集合中
return new StaticSqlSource(configuration, sql, handler.getParameterMappings());
}
调用GenericTokenParser的parse进行解析：
// org.apache.ibatis.parsing.GenericTokenParser#parse
public String parse(String text) {
if (text == null || text.isEmpty()) {
return "";
}
// search open token
int start = text.indexOf(openToken);
if (start == -1) {
return text;
}
char[] src = text.toCharArray();
int offset = 0;
final StringBuilder builder = new StringBuilder();
StringBuilder expression = null;
do {
if (start > 0 && src[start - 1] == '\\') {
// this open token is escaped. remove the backslash and continue.
builder.append(src, offset, start - offset - 1).append(openToken);
offset = start + openToken.length();
} else {
// found open token. let's search close token.
if (expression == null) {
expression = new StringBuilder();
} else {
expression.setLength(0);
}
builder.append(src, offset, start - offset);
offset = start + openToken.length();
int end = text.indexOf(closeToken, offset);
while (end > -1) {
if (end > offset && src[end - 1] == '\\') {
// this close token is escaped. remove the backslash and continue.
expression.append(src, offset, end - offset - 1).append(closeToken);
offset = end + closeToken.length();
end = text.indexOf(closeToken, offset);
} else {
expression.append(src, offset, end - offset);
break;
}
}
if (end == -1) {
// close token was not found.
builder.append(src, start, src.length - start);
offset = src.length;
} else {
builder.append(handler.handleToken(expression.toString())); // 该方法会返回一个 ?
offset = end + closeToken.length();
}
}
start = text.indexOf(openToken, offset);
} while (start > -1);
if (offset < src.length) {
builder.append(src, offset, src.length - offset);
}
return builder.toString();
}
最终相当于是逐个字符进行解析，然后将#{id}替换成了 ?
写在后面
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