Mybatis源码解析
大家应该都知道Mybatis源码也是对Jdbc的再一次封装，不管怎么进行包装，还是会有获取链接、preparedStatement、封装参数、执行这些步骤的。
一、配置解析过程
String resource = "mybatis-config.xml";
// 1. 读取resources下面的mybatis-config.xml文件
InputStream inputStream = Resources.getResourceAsStream(resource);
// 2. 使用SqlSessionFactoryBuilder创建SqlSessionFactory
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
// 3. 通过sqlSessionFactory创建SqlSession
SqlSession sqlSession = sqlSessionFactory.openSession();
1.1 Resources.getResourceAsStream(resource)读取文件
public static InputStream getResourceAsStream(String resource) throws IOException {
return getResourceAsStream(null, resource);
}
// loader赋值为null
public static InputStream getResourceAsStream(ClassLoader loader, String resource)
throws IOException {
InputStream in = classLoaderWrapper.getResourceAsStream(resource, loader);
if (in == null) {
throw new IOException("Could not find resource " + resource);
}
return in;
}
// classLoader为null
public InputStream getResourceAsStream(String resource, ClassLoader classLoader) {
return getResourceAsStream(resource, getClassLoaders(classLoader));
}
// classLoader类加载
InputStream getResourceAsStream(String resource, ClassLoader[] classLoader) {
for (ClassLoader cl : classLoader) {
if (null != cl) {
// 加载指定路径文件流
InputStream returnValue = cl.getResourceAsStream(resource);
// now, some class loaders want this leading "/",
// so we'll add it and try again if we didn't find the resource
if (null == returnValue) {
returnValue = cl.getResourceAsStream("/" + resource);
}
if (null != returnValue) {
return returnValue;
}
}
}
return null;
}
总结：主要是通过ClassLoader.getResourceAsStream()方法获取指定的classpath路径下的Resource。
1.2 通过SqlSessionFactoryBuilder创建SqlSessionFactory
// SqlSessionFactoryBuilder是一个建造者模式
public class SqlSessionFactoryBuilder {
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
public SqlSessionFactory build(InputStream inputStream) {
return build(inputStream, null, null);
}
public SqlSessionFactory build(InputStream inputStream, String environment,
Properties properties) {
try {
XMLConfigBuilder parser = new XMLConfigBuilder(inputStream, environment, properties);
// 其中parser.parse()负责解析xml，build(configuration)创建SqlSessionFactory
return build(parser.parse());
} catch (Exception e) {
throw ExceptionFactory.wrapException("Error building SqlSession.", e);
} finally {
ErrorContext.instance().reset();
try {
inputStream.close();
} catch (IOException e) {
// Intentionally ignore. Prefer previous error.
}
}
}
...
}
// XMLConfigBuilder也是建造者模式
public class XMLConfigBuilder extends BaseBuilder {
// 接下来进入XMLConfigBuilder构造函数
public XMLConfigBuilder(InputStream inputStream, String environment, Properties props) {
this(new XPathParser(inputStream, true, props, new XMLMapperEntityResolver()),
environment, props);
}
// 接下来进入this后，初始化Configuration
private XMLConfigBuilder(XPathParser parser, String environment, Properties props) {
super(new Configuration());
ErrorContext.instance().resource("SQL Mapper Configuration");
this.configuration.setVariables(props);
this.parsed = false;
this.environment = environment;
this.parser = parser;
}
}
1.3 parser.parse()解析xml
public Configuration parse() {
// 判断是否重复解析
if (parsed) {
throw new BuilderException("Each XMLConfigBuilder can only be used once.");
}
parsed = true;
// 读取配置文件一级节点configuration
parseConfiguration(parser.evalNode("/configuration"));
return configuration;
}
private void parseConfiguration(XNode root) {
try {
// properties标签，用来配置参数信息，比如最常见的数据库连接信息
propertiesElement(root.evalNode("properties"));
Properties settings = settingsAsProperties(root.evalNode("settings"));
loadCustomVfs(settings);
loadCustomLogImpl(settings);
// 实体别名两种方式:1.指定单个实体;2.指定包
typeAliasesElement(root.evalNode("typeAliases"));
// 插件
pluginElement(root.evalNode("plugins"));
// 用来创建对象(数据库数据映射成java对象时)
objectFactoryElement(root.evalNode("objectFactory"));
objectWrapperFactoryElement(root.evalNode("objectWrapperFactory"));
reflectorFactoryElement(root.evalNode("reflectorFactory"));
settingsElement(settings);
// read it after objectFactory and objectWrapperFactory issue #631
// 数据库环境
environmentsElement(root.evalNode("environments"));
databaseIdProviderElement(root.evalNode("databaseIdProvider"));
// 数据库类型和Java数据类型的转换
typeHandlerElement(root.evalNode("typeHandlers"));
// 这个是对数据库增删改查的解析
mapperElement(root.evalNode("mappers"));
} catch (Exception e) {
throw new BuilderException("Error parsing SQL Mapper Configuration. Cause: " + e, e);
}
}
总结：parseConfiguration完成的是解析configuration下的标签
private void mapperElement(XNode parent) throws Exception {
if (parent != null) {
for (XNode child : parent.getChildren()) {
// 解析<package name=""/>
if ("package".equals(child.getName())) {
String mapperPackage = child.getStringAttribute("name");
// 包路径存到mapperRegistry中
configuration.addMappers(mapperPackage);
} else {
// 解析<mapper url="" class="" resource=""></mapper>
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);
// 读取Mapper.xml文件
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);
InputStream inputStream = Resources.getUrlAsStream(url);
XMLMapperBuilder mapperParser = new XMLMapperBuilder(inputStream, configuration, url,
configuration.getSqlFragments());
mapperParser.parse();
} 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.");
}
}
}
}
总结：通过解析configuration.xml文件，获取其中的Environment、Setting，重要的是将下的所有解析出来之后添加到Configuration，Configuration类似于配置中心，所有的配置信息都在这里。
1.4 mapperParser.parse()对Mapper映射器的解析
public void parse() {
if (!configuration.isResourceLoaded(resource)) {
// 解析所有的子标签
configurationElement(parser.evalNode("/mapper"));
configuration.addLoadedResource(resource);
// 把namespace(接口类型)和工厂类绑定起来
bindMapperForNamespace();
}
parsePendingResultMaps();
parsePendingCacheRefs();
parsePendingStatements();
}
// 这里面解析的是Mapper.xml的标签
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);
// 对其他命名空间缓存配置的引用
cacheRefElement(context.evalNode("cache-ref"));
// 对给定命名空间的缓存配置
cacheElement(context.evalNode("cache"));
parameterMapElement(context.evalNodes("/mapper/parameterMap"));
// 是最复杂也是最强大的元素，用来描述如何从数据库结果集中来加载对象
resultMapElements(context.evalNodes("/mapper/resultMap"));
// 可被其他语句引用的可重用语句块
sqlElement(context.evalNodes("/mapper/sql"));
// 获得MappedStatement对象(增删改查标签)
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);
}
}
// 获得MappedStatement对象(增删改查标签)
private void buildStatementFromContext(List<XNode> list) {
if (configuration.getDatabaseId() != null) {
buildStatementFromContext(list, configuration.getDatabaseId());
}
buildStatementFromContext(list, null);
}
// 获得MappedStatement对象(增删改查标签)
private void buildStatementFromContext(List<XNode> list, String requiredDatabaseId) {
// 循环增删改查标签
for (XNode context : list) {
final XMLStatementBuilder statementParser = new XMLStatementBuilder(configuration,
builderAssistant, context, requiredDatabaseId);
try {
// 解析insert/update/select/del中的标签
statementParser.parseStatementNode();
} catch (IncompleteElementException e) {
configuration.addIncompleteStatement(statementParser);
}
}
}
public void parseStatementNode() {
// 在命名空间中唯一的标识符，可以被用来引用这条语句
String id = context.getStringAttribute("id");
// 数据库厂商标识
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;
// flushCache和useCache都和二级缓存有关
// 将其设置为true后，只要语句被调用，都会导致本地缓存和二级缓存被清空，默认值:false
boolean flushCache = context.getBooleanAttribute("flushCache", !isSelect);
// 将其设置为true后，将会导致本条语句的结果被二级缓存缓存起来，默认值：对select元素为true
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());
// 会传入这条语句的参数类的完全限定名或别名
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;
}
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");
// 从这条语句中返回的期望类型的类的完全限定名或别名
String resultType = context.getStringAttribute("resultType");
Class<?> resultTypeClass = resolveClass(resultType);
// 外部resultMap的命名引用
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);
}
public MappedStatement addMappedStatement(String id, SqlSource sqlSource, StatementType statementType,
SqlCommandType sqlCommandType, Integer fetchSize, Integer timeout, String parameterMap,
Class<?> parameterType, String resultMap, Class<?> resultType, ResultSetType resultSetType,
boolean flushCache, boolean useCache, boolean resultOrdered, KeyGenerator keyGenerator,
String keyProperty, String keyColumn, String databaseId, LanguageDriver lang,
String resultSets) {
if (unresolvedCacheRef) {
throw new IncompleteElementException("Cache-ref not yet resolved");
}
id = applyCurrentNamespace(id, false);
boolean isSelect = sqlCommandType == SqlCommandType.SELECT;
MappedStatement.Builder statementBuilder = new MappedStatement.Builder(configuration,id, sqlSource,
sqlCommandType).resource(resource).fetchSize(fetchSize).timeout(timeout)
.statementType(statementType).keyGenerator(keyGenerator).keyProperty(keyProperty)
.keyColumn(keyColumn).databaseId(databaseId).lang(lang).resultOrdered(resultOrdered)
.resultSets(resultSets).resultMaps(getStatementResultMaps(resultMap, resultType, id))
.resultSetType(resultSetType).flushCacheRequired(valueOrDefault(flushCache, !isSelect))
.useCache(valueOrDefault(useCache, isSelect)).cache(currentCache);
ParameterMap statementParameterMap = getStatementParameterMap(parameterMap, parameterType, id);
if (statementParameterMap != null) {
statementBuilder.parameterMap(statementParameterMap);
}
MappedStatement statement = statementBuilder.build();
// 持有在configuration中
configuration.addMappedStatement(statement);
return statement;
}
public void addMappedStatement(MappedStatement ms){
// ms.getId = mapper.UserMapper.getUserById
// ms = MappedStatement等于每一个增删改查的标签的里的数据
mappedStatements.put(ms.getId(), ms);
}
// 最终存放到mappedStatements中,mappedStatements存放的是一个个的增删改查
protected final Map<String, MappedStatement> mappedStatements =
new StrictMap<MappedStatement>("Mapped Statements collection")
.conflictMessageProducer((savedValue, targetValue) ->
". please check " + savedValue.getResource() + " and "
+ targetValue.getResource());
1.5 解析bindMapperForNamespace()方法
把namespace(接口类型)和工厂类绑定起来
private void bindMapperForNamespace() {
//当前Mapper的命名空间
String namespace = builderAssistant.getCurrentNamespace();
if (namespace != null) {
Class<?> boundType = null;
try {
//interface mapper.UserMapper这种
boundType = Resources.classForName(namespace);
} catch (ClassNotFoundException e) {
}
if (boundType != null) {
if (!configuration.hasMapper(boundType)) {
configuration.addLoadedResource("namespace:" + namespace);
configuration.addMapper(boundType);
}
}
}
}
public <T> void addMapper(Class<T> type) {
mapperRegistry.addMapper(type);
}
public <T> void addMapper(Class<T> type) {
if (type.isInterface()) {
if (hasMapper(type)) {
throw new BindingException("Type " + type + " is already known to the MapperRegistry.");
}
boolean loadCompleted = false;
try {
//接口类型(key)->工厂类
knownMappers.put(type, new MapperProxyFactory<>(type));
MapperAnnotationBuilder parser = new MapperAnnotationBuilder(config, type);
parser.parse();
loadCompleted = true;
} finally {
if (!loadCompleted) {
knownMappers.remove(type);
}
}
}
}
1.6 生成SqlSessionFactory对象
XMLMapperBuilder.parse()方法，是对Mapper映射器的解析里面有两个方法：
configurationElement()解析所有的子标签，最终解析Mapper.xml中的insert/update/delete/select标签的id(全路径)组成key和整个标签和数据连接组成MappedStatement存放到Configuration中的mappedStatements这个map里面。bindMapperForNamespace()是把接口类型(interface mapper.UserMapper)和工厂类存到放MapperRegistry中的knownMappers里面。
二、SqlSessionFactory的创建
public SqlSessionFactory build(Configuration config) {
return new DefaultSqlSessionFactory(config);
}
直接把Configuration当做参数，直接new一个DefaultSqlSessionFactory。
三、SqlSession会话的创建过程
mybatis操作的时候跟数据库的每一次连接，都需要创建一个会话，我们用openSession()方法来创建。这个会话里面需要包含一个Executor用来执行SQL。Executor又要指定事务类型和执行器的类型。
3.1 创建Transaction(两种方式)
| 属性 | 产生工厂类 | 产生事务 |
|---|---|---|
| JDBC | JdbcTransactionFactory | JdbcTransaction |
| MANAGED | ManagedTransactionFactory | ManagedTransaction |
- 如果配置的是
JDBC，则会使用Connection对象的commit()、rollback()、close()管理事务。 - 如果配置成
MANAGED，会把事务交给容器来管理，比如JBOSS，Weblogic。
SqlSession sqlSession = sqlSessionFactory.openSession();
public SqlSession openSession() {
// configuration中有默认赋值protected ExecutorType defaultExecutorType = ExecutorType.SIMPLE
return openSessionFromDataSource(configuration.getDefaultExecutorType(), null, false);
}
<environments default="development">
<environment id="development">
<transactionManager type="JDBC"/>
<dataSource type="POOLED">
<property name="driver" value="${driver}"/>
<property name="url" value="${url}"/>
<property name="username" value="${username}"/>
<property name="password" value="${password}"/>
</dataSource>
</environment>
</environments>
3.2 创建Executor
// ExecutorType是SIMPLE，一共有三种SIMPLE(SimpleExecutor)、REUSE(ReuseExecutor)、BATCH(BatchExecutor)
private SqlSession openSessionFromDataSource(ExecutorType execType, TransactionIsolationLevel level,
boolean autoCommit) {
Transaction tx = null;
try {
// xml中的development节点
final Environment environment = configuration.getEnvironment();
// type配置的是Jbdc所以生成的是JbdcTransactionFactory工厂类
final TransactionFactory transactionFactory =
getTransactionFactoryFromEnvironment(environment);
// Jdbc生成JbdcTransactionFactory生成JbdcTransaction
tx = transactionFactory.newTransaction(environment.getDataSource(), level, autoCommit);
// 创建CachingExecutor执行器
final Executor executor = configuration.newExecutor(tx, execType);
// 创建DefaultSqlSession属性包括 Configuration、Executor对象
return new DefaultSqlSession(configuration, executor, autoCommit);
} catch (Exception e) {
closeTransaction(tx); // may have fetched a connection so lets call
close()
throw ExceptionFactory.wrapException("Error opening session. Cause: " + e, e);
} finally {
ErrorContext.instance().reset();
}
}
四、获得Mapper对象
UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
public <T> T getMapper(Class<T> type) {
return configuration.getMapper(type, this);
}
mapperRegistry.getMapper是从MapperRegistry的knownMappers里面取的，knownMappers里面存的是接口类型(interface mapper.UserMapper)和工厂类(MapperProxyFactory)。
public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
return mapperRegistry.getMapper(type, sqlSession);
}
从knownMappers的Map里根据接口类型(interface mapper.UserMapper)取出对应的工厂类。
public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
final MapperProxyFactory<T> mapperProxyFactory = (MapperProxyFactory<T>)
knownMappers.get(type);
if (mapperProxyFactory == null) {
throw new BindingException("Type " + type + " is not known to the MapperRegistry.");
}
try {
return mapperProxyFactory.newInstance(sqlSession);
} catch (Exception e) {
throw new BindingException("Error getting mapper instance. Cause: " + e, e);
}
}
public T newInstance(SqlSession sqlSession) {
final MapperProxy<T> mapperProxy = new MapperProxy<>(sqlSession, mapperInterface, methodCache);
return newInstance(mapperProxy);
}
这里通过JDK动态代理返回代理对象MapperProxy(org.apache.ibatis.binding.MapperProxy@6b2ea799)
protected T newInstance(MapperProxy<T> mapperProxy) {
// mapperInterface是interface mapper.UserMapper
return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(), new
Class[] { mapperInterface }, mapperProxy);
}
UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
五、执行SQL
User user = userMapper.getUserById(1);
5.1 调用invoke代理方法
由于所有的Mapper都是MapperProxy代理对象，所以任意的方法都是执行MapperProxy的invoke()方法
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
try {
// 判断是否需要去执行SQL还是直接执行方法
if (Object.class.equals(method.getDeclaringClass())) {
return method.invoke(this, args);
// 这里判断的是接口中的默认方法Default等
} else if (isDefaultMethod(method)) {
return invokeDefaultMethod(proxy, method, args);
}
} catch (Throwable t) {
throw ExceptionUtil.unwrapThrowable(t);
}
// 获取缓存，保存了方法签名和接口方法的关系
final MapperMethod mapperMethod = cachedMapperMethod(method);
return mapperMethod.execute(sqlSession, args);
}
5.2 调用execute方法
这里使用的例子用的是查询所以走的是else分支语句。
public Object execute(SqlSession sqlSession, Object[] args) {
Object result;
// 根据命令类型走不行的操作command.getType()是select
switch (command.getType()) {
case INSERT: {
Object param = method.convertArgsToSqlCommandParam(args);
result = rowCountResult(sqlSession.insert(command.getName(), param));
break;
}
case UPDATE: {
Object param = method.convertArgsToSqlCommandParam(args);
result = rowCountResult(sqlSession.update(command.getName(), param));
break;
}
case DELETE: {
Object param = method.convertArgsToSqlCommandParam(args);
result = rowCountResult(sqlSession.delete(command.getName(), param));
break;
}
case SELECT:
if (method.returnsVoid() && method.hasResultHandler()) {
executeWithResultHandler(sqlSession, args);
result = null;
} else if (method.returnsMany()) {
result = executeForMany(sqlSession, args);
} else if (method.returnsMap()) {
result = executeForMap(sqlSession, args);
} else if (method.returnsCursor()) {
result = executeForCursor(sqlSession, args);
} else {
// 将参数转换为SQL的参数
Object param = method.convertArgsToSqlCommandParam(args);
result = sqlSession.selectOne(command.getName(), param);
if (method.returnsOptional()
&& (result == null || !method.getReturnType().equals(result.getClass()))) {
result = Optional.ofNullable(result);
}
}
break;
case FLUSH:
result = sqlSession.flushStatements();
break;
default:
throw new BindingException("Unknown execution method for: " + command.getName());
}
if (result == null && method.getReturnType().isPrimitive() && !method.returnsVoid()) {
throw new BindingException("Mapper method '" + command.getName()
+ " attempted to return null from a method with a primitive return type ("
+ method.getReturnType() + ").");
}
return result;
}
5.3 调用selectOne其实是selectList
selectOne查询一个和查询多个其实是一样的。
public <T> T selectOne(String statement, Object parameter) {
// Popular vote was to return null on 0 results and throw exception on too many.
List<T> list = this.selectList(statement, parameter);
if (list.size() == 1) {
return list.get(0);
} else if (list.size() > 1) {
throw new TooManyResultsException("Expected one result (or null) to be returned"
+ " by selectOne(), but found: " + list.size());
} else {
return null;
}
}
public <E> List<E> selectList(String statement, Object parameter, RowBounds rowBounds) {
try {
// 从Configuration里的mappedStatements里根据key(id的全路径)获取MappedStatement对象
MappedStatement ms = configuration.getMappedStatement(statement);
return executor.query(ms, wrapCollection(parameter), rowBounds, Executor.NO_RESULT_HANDLER);
} catch (Exception e) {
throw ExceptionFactory.wrapException("Error querying database. Cause: " + e, e);
} finally {
ErrorContext.instance().reset();
}
}
5.4 mappedStatements对象
在org.apache.ibatis.session.Configuration中通过MapperBuilderAssistant创建的MappedStatement对象，添加到configuration.mappedStatements集合中保存
protected final Map<String, MappedStatement> mappedStatements;
5.5 MappedStatement对象
private String resource;//mapper配置文件名，如：UserMapper.xml
private Configuration configuration;//全局配置
private String id;//节点的id属性加命名空间，如：com.lucky.mybatis.dao.UserMapper.selectByExample
private Integer fetchSize;
private Integer timeout;//超时时间
private StatementType statementType;//操作SQL的对象的类型
private ResultSetType resultSetType;//结果类型
private SqlSource sqlSource;//sql语句
private Cache cache;//缓存
private ParameterMap parameterMap;
private List<ResultMap> resultMaps;
private boolean flushCacheRequired;
private boolean useCache;//是否使用缓存，默认为true
private boolean resultOrdered;//结果是否排序
private SqlCommandType sqlCommandType;//sql语句的类型，如select、update、delete、insert
private KeyGenerator keyGenerator;
private String[] keyProperties;
private String[] keyColumns;
private boolean hasNestedResultMaps;
private String databaseId;//数据库ID
private Log statementLog;
private LanguageDriver lang;
private String[] resultSets;
六、执行query方法
6.1 创建CacheKey
从BoundSql中获取SQL信息，创建CacheKey。这个CacheKey就是缓存的Key。
public <E> List<E> query(MappedStatement ms, Object parameterObject, RowBounds rowBounds,
ResultHandler resultHandler) throws SQLException {
// 创建缓存Key
BoundSql boundSql = ms.getBoundSql(parameterObject);
// key = -575461213:-771016147:mapper.UserMapper.getUserById:0:2147483647:
// select * from test_user where id = ?:1:development
CacheKey key = createCacheKey(ms, parameterObject, rowBounds, boundSql);
return query(ms, parameterObject, rowBounds, resultHandler, key, boundSql);
}
public <E> List<E> query(MappedStatement ms, Object parameterObject, RowBounds rowBounds,
ResultHandler resultHandler, CacheKey key, BoundSql boundSql) throws SQLException {
Cache cache = ms.getCache();
if (cache != null) {
flushCacheIfRequired(ms);
if (ms.isUseCache() && resultHandler == null) {
ensureNoOutParams(ms, boundSql);
@SuppressWarnings("unchecked")
List<E> list = (List<E>) tcm.getObject(cache, key);
if (list == null) {
list = delegate.query(ms, parameterObject, rowBounds, resultHandler, key, boundSql);
tcm.putObject(cache, key, list); // issue #578 and #116
}
return list;
}
}
return delegate.query(ms, parameterObject, rowBounds, resultHandler, key, boundSql);
}
6.2 清空本地缓存
public <E> List<E> query(MappedStatement ms, Object parameter, RowBounds rowBounds,
ResultHandler resultHandler, CacheKey key, BoundSql boundSql) throws SQLException {
ErrorContext.instance().resource(ms.getResource()).activity("executing a query")
.object(ms.getId());
if (closed) {
throw new ExecutorException("Executor was closed.");
}
// queryStack用于记录查询栈，防止递归查询重复处理缓存
// flushCache=true的时候，会先清理本地缓存(一级缓存)
if (queryStack == 0 && ms.isFlushCacheRequired()) {
// 清空本地缓存
clearLocalCache();
}
List<E> list;
try {
queryStack++;
list = resultHandler == null ? (List<E>) localCache.getObject(key) : null;
if (list != null) {
handleLocallyCachedOutputParameters(ms, key, parameter, boundSql);
} else {
// 如果没有缓存，会从数据库查询：queryFromDatabase()
list = queryFromDatabase(ms, parameter, rowBounds, resultHandler, key, boundSql);
}
} finally {
queryStack--;
}
if (queryStack == 0) {
for (DeferredLoad deferredLoad : deferredLoads) {
deferredLoad.load();
}
// issue #601
deferredLoads.clear();
// 如果LocalCacheScope == STATEMENT，会清理本地缓存
if (configuration.getLocalCacheScope() == LocalCacheScope.STATEMENT) {
// issue #482
clearLocalCache();
}
}
return list;
}
6.3 从数据库查询
private <E> List<E> queryFromDatabase(MappedStatement ms, Object parameter, RowBounds rowBounds,
ResultHandler resultHandler, CacheKey key, BoundSql boundSql) throws SQLException {
List<E> list;
// 先在缓存用占位符占位
localCache.putObject(key, EXECUTION_PLACEHOLDER);
try {
// 执行Executor的doQuery()，默认是SimpleExecutor
list = doQuery(ms, parameter, rowBounds, resultHandler, boundSql);
} finally {
// 执行查询后，移除占位符
localCache.removeObject(key);
}
// 从新放入数据
localCache.putObject(key, list);
if (ms.getStatementType() == StatementType.CALLABLE) {
localOutputParameterCache.putObject(key, parameter);
}
return list;
}
6.4 执行doQuery
public <E> List<E> doQuery(MappedStatement ms, Object parameter, RowBounds rowBounds,
ResultHandler resultHandler, BoundSql boundSql) throws SQLException {
Statement stmt = null;
try {
Configuration configuration = ms.getConfiguration();
StatementHandler handler = configuration.newStatementHandler(wrapper, ms, parameter,
rowBounds, resultHandler, boundSql);
stmt = prepareStatement(handler, ms.getStatementLog());
return handler.query(stmt, resultHandler);
} finally {
closeStatement(stmt);
}
}
