MyBatis印象阅读之Mapper解析（下）
2019-08-01 本文已影响0人
向光奔跑_
在上一章中我们讲述在Mapper资源文件解析过程中的ResultMap的解析过程，本章我们来收个尾，把剩下的解析全部讲完。
还记得：
// XMLMapperBuilder
private void configurationElement(XNode context) {
try {
String namespace = context.getStringAttribute("namespace");
if (namespace == null || namespace.equals("")) {
throw new BuilderException("Mapper's namespace cannot be empty");
}
builderAssistant.setCurrentNamespace(namespace);
cacheRefElement(context.evalNode("cache-ref"));
cacheElement(context.evalNode("cache"));
parameterMapElement(context.evalNodes("/mapper/parameterMap"));
resultMapElements(context.evalNodes("/mapper/resultMap"));
sqlElement(context.evalNodes("/mapper/sql"));
buildStatementFromContext(context.evalNodes("select|insert|update|delete"));
} catch (Exception e) {
throw new BuilderException("Error parsing Mapper XML. The XML location is '" + resource + "'. Cause: " + e, e);
}
}
代码么，我们在之前已经分析到了resultMapElements过程，接下来我们继续分析。
1. XMLMapperBuilder的sqlElement方法解析
private void sqlElement(List<XNode> list) {
if (configuration.getDatabaseId() != null) {
sqlElement(list, configuration.getDatabaseId());
}
sqlElement(list, null);
}
private void sqlElement(List<XNode> list, String requiredDatabaseId) {
for (XNode context : list) {
String databaseId = context.getStringAttribute("databaseId");
String id = context.getStringAttribute("id");
id = builderAssistant.applyCurrentNamespace(id, false);
if (databaseIdMatchesCurrent(id, databaseId, requiredDatabaseId)) {
sqlFragments.put(id, context);
}
}
}
这里我们分析下：
- 在逻辑上还是比较简单的，这里主要会有一个databaseId会干扰我们更好的理解阅读，其实你可以把这个相关的代码去掉，那么到最后其实就剩下了 sqlFragments.put(id, context)这个代码
- 重点逻辑也就是在xml使用sql标签里的内容，放入到sqlFragments变量中。
就这么简单的把今天二分之一的工作量分析完了，开心~~~我们继续往下分析buildStatementFromContext方法。
2. XMLMapperBuilder的buildStatementFromContext方法解析
private void buildStatementFromContext(List<XNode> list) {
if (configuration.getDatabaseId() != null) {
buildStatementFromContext(list, configuration.getDatabaseId());
}
buildStatementFromContext(list, null);
}
private void buildStatementFromContext(List<XNode> list, String requiredDatabaseId) {
for (XNode context : list) {
final XMLStatementBuilder statementParser = new XMLStatementBuilder(configuration, builderAssistant, context, requiredDatabaseId);
try {
statementParser.parseStatementNode();
} catch (IncompleteElementException e) {
configuration.addIncompleteStatement(statementParser);
}
}
}
跟上面的sqlElement源码类似，当我们去掉databaseId这个平常来讲对我们无关紧要的代码后，逻辑其实就剩下了XMLStatementBuilder类了。
2.1 XMLStatementBuilder源码分析
我们先来看属性和构造方法：
private final MapperBuilderAssistant builderAssistant;
private final XNode context;
private final String requiredDatabaseId;
public XMLStatementBuilder(Configuration configuration, MapperBuilderAssistant builderAssistant, XNode context, String databaseId) {
super(configuration);
this.builderAssistant = builderAssistant;
this.context = context;
this.requiredDatabaseId = databaseId;
}
在来看上面调用的方法parseStatementNode：
public void parseStatementNode() {
String id = context.getStringAttribute("id");
String databaseId = context.getStringAttribute("databaseId");
if (!databaseIdMatchesCurrent(id, databaseId, this.requiredDatabaseId)) {
return;
}
//获取node的DML标签并解析
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
//<1>解析<include>标签
XMLIncludeTransformer includeParser = new XMLIncludeTransformer(configuration, builderAssistant);
includeParser.applyIncludes(context.getNode());
String parameterType = context.getStringAttribute("parameterType");
Class<?> parameterTypeClass = resolveClass(parameterType);
//LanguageDriver我没用到过，所以不做解析
String lang = context.getStringAttribute("lang");
LanguageDriver langDriver = getLanguageDriver(lang);
// Parse selectKey after includes and remove them.
//解析<selectKey>标签在<include>之后，问题：如果先解析<selectKey>标签，在解析<include>标签，可行否？
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;
}
//解析动态Sql
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);
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);
}
我们先来看<1>处逻辑：
这里是在解析<include>标签，我们深入来看XMLIncludeTransformer类：
继续来看属性和构造方法：
// XMLIncludeTransformer
private final Configuration configuration;
private final MapperBuilderAssistant builderAssistant;
public XMLIncludeTransformer(Configuration configuration, MapperBuilderAssistant builderAssistant) {
this.configuration = configuration;
this.builderAssistant = builderAssistant;
}
继续来看它的调用方法：
public void applyIncludes(Node source) {
Properties variablesContext = new Properties();
Properties configurationVariables = configuration.getVariables();
Optional.ofNullable(configurationVariables).ifPresent(variablesContext::putAll);
applyIncludes(source, variablesContext, false);
}
/**
* Recursively apply includes through all SQL fragments.
* @param source Include node in DOM tree
* @param variablesContext Current context for static variables with values
*/
private void applyIncludes(Node source, final Properties variablesContext, boolean included) {
if (source.getNodeName().equals("include")) {
//<1>查询对应的sqlfragment
Node toInclude = findSqlFragment(getStringAttribute(source, "refid"), variablesContext);
Properties toIncludeContext = getVariablesContext(source, variablesContext);
//<2>
applyIncludes(toInclude, toIncludeContext, true);
if (toInclude.getOwnerDocument() != source.getOwnerDocument()) {
toInclude = source.getOwnerDocument().importNode(toInclude, true);
}
source.getParentNode().replaceChild(toInclude, source);
while (toInclude.hasChildNodes()) {
toInclude.getParentNode().insertBefore(toInclude.getFirstChild(), toInclude);
}
toInclude.getParentNode().removeChild(toInclude);
} else if (source.getNodeType() == Node.ELEMENT_NODE) {
if (included && !variablesContext.isEmpty()) {
// replace variables in attribute values
NamedNodeMap attributes = source.getAttributes();
for (int i = 0; i < attributes.getLength(); i++) {
Node attr = attributes.item(i);
attr.setNodeValue(PropertyParser.parse(attr.getNodeValue(), variablesContext));
}
}
NodeList children = source.getChildNodes();
for (int i = 0; i < children.getLength(); i++) {
applyIncludes(children.item(i), variablesContext, included);
}
} else if (included && source.getNodeType() == Node.TEXT_NODE
&& !variablesContext.isEmpty()) {
// replace variables in text node
source.setNodeValue(PropertyParser.parse(source.getNodeValue(), variablesContext));
}
}
- 第<1>处：
private Node findSqlFragment(String refid, Properties variables) {
refid = PropertyParser.parse(refid, variables);
refid = builderAssistant.applyCurrentNamespace(refid, true);
try {
XNode nodeToInclude = configuration.getSqlFragments().get(refid);
return nodeToInclude.getNode().cloneNode(true);
} catch (IllegalArgumentException e) {
throw new IncompleteElementException("Could not find SQL statement to include with refid '" + refid + "'", e);
}
}
不知还记得否在本章开篇分析的sqlFragment解析，这里就是通过refid直接获取。
- 第<2>处代码的源码我就不贴了，看了会影响你阅读的兴趣，功能是解析${}的变量替换对应的内容。
之后的内容就比较无关了。
讲完了关于XMLIncludeTransformer类的解释，我们可以看到下面是分别解析了KeyGenerator和SqlSource，最后组装成了MappedStatement。后面会详细讲解，这里就不做展示了。
3. 今日总结
我们把剩下的mapper解析方法都已经讲完了，虽然很多重要解析我们都没有深入分析，可能会让你觉得很不爽，但是我们得一步步来，一口吃成胖子做不到。好啦，那你今天会有收货么？
