您的位置：首页 > 数据库

[置顶] MyBatis（三） xml文件解析流程动态SQL解析

2017-05-23 16:34 417 查看

1.MyBatis将整个系统串联起来的就是Configure对象这个需要牢记。在前面MyBatis xml文件解析流程(二) Mapper解析中介绍了Mapper的解析入口，以及Mapper文件中各个节点的解析方法。里面有几个类需要总结下

BaseBuilder:作为其他Builder类的基类

2.XMLConfigBuilder:在Configuration解析时介绍过，主要用来解析config配置文件下的Configuration节点，内部会使用XMLMapperBuilder用于解析xml文件

3.XMLMapperBuilder:在Mapper解析中也介绍过。主要用来解析Mapper文件的，里面用，内部会使用XMLStatementBuilder来处理节点

4.XMLStatementBuilder:解析select|insert|update|delete节点，内部会使用XMLScriptBuilder解析xml节点

5.XMLScriptBuilder:解析sql中各个其他的节点并把解析结果保存到SqlNode中。

6.MapperBuilderAssistant:这是mapper解析中的关键，他作为mapper解析的助理类，负责将解析出来的结果保存下来，并且通过configuration.addMappedStatement方法保存到conguration对象中，最终在调用dao是根据传入的参数动态生成sql。所以说configuration是MyBatis调用的调配中心。

2.动态sql解析流程分析

2.1 从XMLMapperBuilder类中configurationElement方法是mapper文件解析开始。

private void configurationElement(XNode context) {
try {
String namespace = context.getStringAttribute("namespace");
if (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"));
//sql insert|select|update|delete节点解析入口
buildStatementFromContext(context.evalNodes("select|insert|update|delete"));
} catch (Exception e) {
throw new BuilderException("Error parsing Mapper XML. Cause: " + e, e);
}
}

2.2调用buildStatementFromContext方法,将配置文件中的insert|select|update|delete保存到list集合中，并且通过buildStatementFromContext方法进行循环解析所有节点

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) {
//创建XMLStatementBuilder 实例
final XMLStatementBuilder statementParser = new XMLStatementBuilder(configuration, builderAssistant, context, requiredDatabaseId);
try {
//进行解析
statementParser.parseStatementNode();
} catch (IncompleteElementException e) {
configuration.addIncompleteStatement(statementParser);
}
}
}

2.3 此处XMLStatementBuilder(configuration, builderAssistant, context,requiredDatabaseId)引出来XMLStatementBuilder ， MapperBuilderAssistant类，上面介绍过这两个类的作用，XMLStatementBuilder 的parseStatementNode方法负责即解析sql节点。

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");
StatementType statementType = StatementType.valueOf(context.getStringAttribute("statementType", StatementType.PREPARED.toString()));
ResultSetType resultSetTypeEnum = resolveResultSetType(resultSetType);

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());

// Parse selectKey after includes,
// in case if IncompleteElementException (issue #291)
List<XNode> selectKeyNodes = context.evalNodes("selectKey");
if (configuration.getDatabaseId() != null) {
parseSelectKeyNodes(id, selectKeyNodes, parameterTypeClass, langDriver, configuration.getDatabaseId());
}
parseSelectKeyNodes(id, selectKeyNodes, parameterTypeClass, langDriver, null);

// 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");
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();
}
//MapperBuilderAssistant将解析信息保存并且与configuration关联起来，在后面调用mapper接口时会根据这里保存的信息，以及用户传入的参数来进行动态生成sql后面会说到。
builderAssistant.addMappedStatement(id, sqlSource, statementType, sqlCommandType,
fetchSize, timeout, parameterMap, parameterTypeClass, resultMap, resultTypeClass,
resultSetTypeEnum, flushCache, useCache, resultOrdered,
keyGenerator, keyProperty, keyColumn, databaseId, langDriver, resultSets);
}

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

很重要，我们看下这个SqlSouse是如何生成的。

langDriver我们看其子类XMLLanguageDriver。在XMLLanguageDriver使用XMLScriptBuilder并传入了Configuration ，以及XNode 节点parameterType

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

2.5 XMLScriptBuilder的parseScriptNode方法

public SqlSource parseScriptNode() {
//进行解析节点并返回sqlnode集合
List<SqlNode> contents = parseDynamicTags(context);
//MixedSqlNode 负责对所有不同的SqlNode进行遍历并且调用他们的apply方法此时并没有调用只是将其保存到sqlSource 中，等待将来用户调用时执行MixedSqlNode apply方法
MixedSqlNode rootSqlNode = new MixedSqlNode(contents);
//返回的是动态DynamicSqlSource
SqlSource sqlSource = new DynamicSqlSource(configuration, rootSqlNode);
return sqlSource;
}

2.6 SqlNode介绍

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();
//如果节点类型是CDATA类型或者是TEXT_NODE则创建TextNode
if (child.getNode().getNodeType() == Node.CDATA_SECTION_NODE
|| child.getNode().getNodeType() == Node.TEXT_NODE) {
String data = child.getStringBody("");
contents.add(new TextSqlNode(data));
} else if (child.getNode().getNodeType() == Node.ELEMENT_NODE && !"selectKey".equals(nodeName)) { // issue #628
//如果是ELEMENT_NODE 类型则根据nodeName,根据nodename获取不同的NodeHandler
NodeHandler handler = nodeHandlers.get(nodeName);
if (handler == null) {
throw new BuilderException("Unknown element <" + nodeName + "> in SQL statement.");
}
handler.handleNode(child, contents);
}
}
return contents;
}

获取不同的NodeHandler

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

{
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());
}
};

以上就完成了sql的解析操作

2.8 介绍MixedSqlNode ，其中apply用于遍历所有sqlnode节点

public MixedSqlNode(List<SqlNode> contents) {
this.contents = contents;
}

public boolean apply(DynamicContext context) {
for (SqlNode sqlNode : contents) {
sqlNode.apply(context);
}
return true;
}

内容来自用户分享和网络整理，不保证内容的准确性，如有侵权内容，可联系管理员处理

标签：

相关文章推荐

新的分享

章节导航

[置顶] MyBatis（三） xml文件解析流程 动态SQL解析

[置顶] MyBatis（三） xml文件解析流程动态SQL解析