MyBatis
一款優秀的持久層框架，它支持定製化 SQL、存儲過程以及高級映射。MyBatis 避免了幾乎全部的 JDBC 代碼和手動設置參數以及獲取結果集。MyBatis 可使用簡單的 XML 或註解來配置和映射原生類型、接口和 Java 的 POJO（Plain Old Java Objects，普通老式 Java 對象）爲數據庫中的記錄。（摘抄至官網）html
前言：若是您對MyBatis的底層感興趣，想知道發起一條Sql語句執行，底層走了什麼操做，那您能夠花點時間，認真閱讀下本篇文章，相信會給你很多收穫的。本篇文章步驟條例很清晰的。java
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MyBatis底層是怎麼運行的呢？
public static void main(String[] args) throws IOException {
String configName = "mybatis_config.xml";
Reader reader = Resources.getResourceAsReader(configName);
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);
}
1：啓動，加載配置文件
- new SqlSessionFactoryBuilder().build(reader)，SqlSessionFactoryBuilder建立出SqlSessionFactory，reader參數接收一個mybatis-config.xml的流文件。
- 建立 XMLConfigBuilder：config.xml解析器。
- 實例化 XMLConfigBuilder父類(BaseBuilder)的Configuration類。
- 解析config.xml數據，加載到Configuration對象中。
- new DefaultSqlSessionFactory(config) 建立一個SqlSessionFactory實例，默認是DefaultSqlSessionFactory。
如圖所示
apache
1.1：new SqlSessionFactoryBuilder().build(reader)
建立SqlSessionFactory對象實例
數組
1.2：new XMLConfigBuilder(reader, environment, properties);
解析 mybatis-config.xml文件緩存
public class XMLConfigBuilder extends BaseBuilder {
/* 標記是否已經解析過配置文件 */
private boolean parsed;
/* 解析器 */
private final XPathParser parser;
/**
* 數據源，SqlSessionFactoryBuilder.build(Reader reader, String environment, Properties properties)
* 不指定爲空
*/
private String environment;
public XMLConfigBuilder(XPathParser parser, String environment, Properties props) {
/* 初始化 Configuration */
super(new Configuration());
ErrorContext.instance().resource("SQL Mapper Configuration");
/* 設置格外的屬性 */
this.configuration.setVariables(props);
/* 標記初始化爲 false */
this.parsed = false;
this.environment = environment;
this.parser = parser;
}
}
1.3：new Configuration()
建立 Configuration 實例bash
public class Configuration {
/**
* 類型別名註冊
* 好比 <dataSource type="POOLED">
* 其中的 type="POOLED" 會使用 PooledDataSourceFactory類建立數據源鏈接池
*/
protected final TypeAliasRegistry typeAliasRegistry = new TypeAliasRegistry();
protected final LanguageDriverRegistry languageRegistry = new LanguageDriverRegistry();
public Configuration() {
/**
* JDBC 對應使用的 事務工廠類
* <transactionManager type="JDBC"></transactionManager>
*/
typeAliasRegistry.registerAlias("JDBC", JdbcTransactionFactory.class);
/**
* MANAGED 對應使用的 事務工廠類
*/
typeAliasRegistry.registerAlias("MANAGED", ManagedTransactionFactory.class);
/**
* JNDI 對應使用的 數據源
*/
typeAliasRegistry.registerAlias("JNDI", JndiDataSourceFactory.class);
/**
* POOLED 對應使用的 數據源
* <dataSource type="POOLED">
*/
typeAliasRegistry.registerAlias("POOLED", PooledDataSourceFactory.class);
/**
* UNPOOLED 對應使用的 數據源
*/
typeAliasRegistry.registerAlias("UNPOOLED", UnpooledDataSourceFactory.class);
/**
* 緩存策略
*/
typeAliasRegistry.registerAlias("PERPETUAL", PerpetualCache.class);
typeAliasRegistry.registerAlias("FIFO", FifoCache.class);
typeAliasRegistry.registerAlias("LRU", LruCache.class);
typeAliasRegistry.registerAlias("SOFT", SoftCache.class);
typeAliasRegistry.registerAlias("WEAK", WeakCache.class);
typeAliasRegistry.registerAlias("DB_VENDOR", VendorDatabaseIdProvider.class);
typeAliasRegistry.registerAlias("XML", XMLLanguageDriver.class);
typeAliasRegistry.registerAlias("RAW", RawLanguageDriver.class);
/**
* 日誌
*/
typeAliasRegistry.registerAlias("SLF4J", Slf4jImpl.class);
typeAliasRegistry.registerAlias("COMMONS_LOGGING", JakartaCommonsLoggingImpl.class);
typeAliasRegistry.registerAlias("LOG4J", Log4jImpl.class);
typeAliasRegistry.registerAlias("LOG4J2", Log4j2Impl.class);
typeAliasRegistry.registerAlias("JDK_LOGGING", Jdk14LoggingImpl.class);
typeAliasRegistry.registerAlias("STDOUT_LOGGING", StdOutImpl.class);
typeAliasRegistry.registerAlias("NO_LOGGING", NoLoggingImpl.class);
typeAliasRegistry.registerAlias("CGLIB", CglibProxyFactory.class);
typeAliasRegistry.registerAlias("JAVASSIST", JavassistProxyFactory.class);
languageRegistry.setDefaultDriverClass(XMLLanguageDriver.class);
languageRegistry.register(RawLanguageDriver.class);
}
}
1.4 XMLConfigBuilder.parse()
解析 mybatis-config.xml
session
private void parseConfiguration(XNode root) {
try {
//issue #117 read properties first
/**
* 解析 <properties resource="my.properties" /> 配置文件
*/
propertiesElement(root.evalNode("properties"));
/**
* 解析settings配置文件
* <settings>
* <setting name="logImpl" value="STDOUT_LOGGING"/>
* </settings>
*/
Properties settings = settingsAsProperties(root.evalNode("settings"));
loadCustomVfs(settings);
loadCustomLogImpl(settings);
/**
* 解析 typeAliases配置文件
*/
typeAliasesElement(root.evalNode("typeAliases"));
/**
* 解析 plugins 配置文件
* 這個是插件，能夠動態的攔截sql執行
*/
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"));
/**
* 加載 mapper.xml 文件
*/
mapperElement(root.evalNode("mappers"));
} catch (Exception e) {
throw new BuilderException("Error parsing SQL Mapper Configuration. Cause: " + e, e);
}
}
1.4.1： mapperElement(root.evalNode(「mappers」));
解析mapper.xml文件，以及接口方法的註解mybatis
public class XMLConfigBuilder extends BaseBuilder {
/**
* mapper隱射文件解析
* @param parent
* @throws Exception
*/
private void mapperElement(XNode parent) throws Exception {
if (parent != null) {
for (XNode child : parent.getChildren()) {
/**
* 解析 <package
* <mappers>
* <package name="com.mapper"/>
* </mappers>
*/
if ("package".equals(child.getName())) {
String mapperPackage = child.getStringAttribute("name");
/**
* 添加全部包下的接口
* 實際調用 configuration.addMapper(mapperInterface);
*/
configuration.addMappers(mapperPackage);
} else {
String resource = child.getStringAttribute("resource");
String url = child.getStringAttribute("url");
String mapperClass = child.getStringAttribute("class");
/**
* 解析 <mapper resource
* <mappers>
* <mapper resource="mapper/UserMapper.xml"/>
* </mappers>
*/
if (resource != null && url == null && mapperClass == null) {
ErrorContext.instance().resource(resource);
InputStream inputStream = Resources.getResourceAsStream(resource);
/**
* mapper.xml 解析器
*/
XMLMapperBuilder mapperParser = new XMLMapperBuilder(inputStream, configuration, resource, configuration.getSqlFragments());
/**
* 開始解析 mapper.xml文件
* 重點分析這個 一樣也會調用 configuration.addMapper(mapperInterface); 這個方法
*/
mapperParser.parse();
} else if (resource == null && url != null && mapperClass == null) {
/**
* 解析 <mapper url
*/
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) {
/**
* 解析 <mapper class
*/
Class<?> mapperInterface = Resources.classForName(mapperClass);
configuration.addMapper(mapperInterface);
} else {
/**
* 如下代碼能夠看出 url resource class 三個屬性只能選擇一個，不然就會報錯
*/
throw new BuilderException("A mapper element may only specify a url, resource or class, but not more than one.");
}
}
}
}
}
}
1.4.2：mapperParser.parse();解析
個人UserMapper.xml文件內容爲：
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.mapper.UserMapper">
<select id="findById" resultType="com.entity.User">
select * from `user` where userId = #{userId}
</select>
</mapper>
UserMapper接口內容爲：
package com.mapper;
import com.entity.User;
import org.apache.ibatis.annotations.Select;
public interface UserMapper {
@Select("select * from `user` where userId = 2")
User findById(int userId);
}
疑問？UserMapper.xml有<select id=「findById」，而在接口中的findById方法我又加了一個@Select註解；那麼執行會選擇哪一條Sql執行仍是報錯呢？
以UserMapper.xml爲例子解析，能夠看到 resource = mapper/UserMapper.xml
public class XMLMapperBuilder extends BaseBuilder {
public void parse() {
if (!configuration.isResourceLoaded(resource)) {
/**
* 解析 mapper.xml文件內容
*/
configurationElement(parser.evalNode("/mapper"));
configuration.addLoadedResource(resource);
/**
* 解析 mapper.xml的<mapper namespace="com.mapper.UserMapper">
* namespace指定的{UserMapper}接口的註解信息
*/
bindMapperForNamespace();
}
parsePendingResultMaps();
parsePendingCacheRefs();
parsePendingStatements();
}
}
1.4.3：configurationElement(parser.evalNode("/mapper"));
解析 mapper.xml文件內容
public class XMLMapperBuilder extends BaseBuilder {
private void configurationElement(XNode context) {
try {
/**
* namespace屬性
*/
String namespace = context.getStringAttribute("namespace");
if (namespace == null || namespace.equals("")) {
/**
* 不指定 namespace會報錯哦 由此得知 namespace屬性是必須指定的
*/
throw new BuilderException("Mapper's namespace cannot be empty");
}
builderAssistant.setCurrentNamespace(namespace);
/**
* 解析 cache-ref
*/
cacheRefElement(context.evalNode("cache-ref"));
/**
* 解析 cache
*/
cacheElement(context.evalNode("cache"));
/**
* 解析 parameterMap
*/
parameterMapElement(context.evalNodes("/mapper/parameterMap"));
/**
* 解析 resultMap
*/
resultMapElements(context.evalNodes("/mapper/resultMap"));
/**
* 解析 sql
*/
sqlElement(context.evalNodes("/mapper/sql"));
/**
* 解析 sql語句 select|insert|update|delete
* 重點分析這裏，這裏的解析會關聯到 mapper接口的執行方法 sql語句映射
*/
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);
}
}
}
1.4.4：buildStatementFromContext(context.evalNodes(「select|insert|update|delete」));
解析 sql語句 select|insert|update|delete；list參數內容是select|insert|update|delete的Sql語句
XMLStatementBuilder Sql語句的解析器
1.4.5：statementParser.parseStatementNode();解析Sql語句
builderAssistant.addMappedStatement,並非添加一個mapper.xml文件隱射的實例，而是爲每個Sql語句建立一個實例
public class XMLStatementBuilder extends BaseBuilder {
private final MapperBuilderAssistant builderAssistant;
public void parseStatementNode() {
/**
* 此處省略一大推代碼...
*/
/**
* <select id="findById" resultType="com.entity.User">
* select * from `user` where userId = #{userId}
* </select>
* 參數解析
*
* id：標籤指定的id = findById
* sqlSource：Sql語句，Sql參數佔位
* statementType：sql執行類型 參考{@link StatementType}
* STATEMENT: 直接操做sql，不進行預編譯 ${}
* PREPARED: 預處理，參數，進行預編譯 #{}
* CALLABLE: 執行存儲過程
* sqlCommandType：sql語句類型 參考{@link SqlCommandType}
* UNKNOWN：未知，INSERT：新增，UPDATE：修改，DELETE：刪除，SELECT：查詢，FLUSH：刷新
*
* 其餘參數可查看官網：https://mybatis.org/mybatis-3/zh/sqlmap-xml.html
*/
builderAssistant.addMappedStatement(id, sqlSource, statementType, sqlCommandType,
fetchSize, timeout, parameterMap, parameterTypeClass, resultMap, resultTypeClass,
resultSetTypeEnum, flushCache, useCache, resultOrdered,
keyGenerator, keyProperty, keyColumn, databaseId, langDriver, resultSets);
}
}
1.4.6：builderAssistant.addMappedStatement();
建立一個MappedStatement實例添加到 Configuration.mappedStatements的Map集合中
public class XMLStatementBuilder extends BaseBuilder {
public MappedStatement addMappedStatement() {
/**
* 此處省略一大推代碼...
*/
MappedStatement.Builder statementBuilder = new MappedStatement.Builder(configuration, id, sqlSource, sqlCommandType)
/**
* 建造者模式
* 用於設置 MappedStatement的屬性
* 此處省略一大推代碼...
*/
/**
* 設置參數入參類型 parameterType屬性
* <select id="findById" parameterType="int" resultType="com.entity.User">
* select * from `user` where userId = #{userId}
* </select>
*/
ParameterMap statementParameterMap = getStatementParameterMap(parameterMap, parameterType, id);
if (statementParameterMap != null) {
statementBuilder.parameterMap(statementParameterMap);
}
/**
* 建立一個 {@link MappedStatement} 實例
*/
MappedStatement statement = statementBuilder.build();
/**
* MappedStatement實例添加到 {@link #configuration.mappedStatements} Map集合中
* MappedStatement 是對應一個Sql語句的實例對象
*
* configuration.mappedStatements 存放全部的MappedStatement實例，後面會詳細介紹
*/
configuration.addMappedStatement(statement);
return statement;
}
}
以上流程執行完後，又回到1.4.2：mapperParser.parse();解析，如今開始解析 namespace指定的接口的註解信息，並建立該接口的代理工廠對象，UserMapper接口。
1.4.7：bindMapperForNamespace();
開始解析接口註解，並添加一個MapperProxyFactory代理工廠的對象到configuration.mapperRegistry.knownMappers；key是Mapper接口
public class XMLMapperBuilder extends BaseBuilder {
private void bindMapperForNamespace() {
String namespace = builderAssistant.getCurrentNamespace();
if (namespace != null) {
Class<?> boundType = null;
try {
/**
* java 反射 Class.classForName
*/
boundType = Resources.classForName(namespace);
} catch (ClassNotFoundException e) {
/**
* 這裏並無拋出異常，說明 namespace 能夠指定一個不存在的接口
*/
//ignore, bound type is not required 忽略，綁定類型不是必需的
}
if (boundType != null) {
if (!configuration.hasMapper(boundType)) {
// Spring may not know the real resource name so we set a flag
// to prevent loading again this resource from the mapper interface
// look at MapperAnnotationBuilder#loadXmlResource
configuration.addLoadedResource("namespace:" + namespace);
/**
* 添加一個Mapper接口的代理工廠對象到configuration.mapperRegistry.knownMappers集合中
* 參考 {@link Configuration#mapperRegistry},
* {@link MapperRegistry#knownMappers}
*/
configuration.addMapper(boundType);
}
}
}
}
}
1.4.8：configuration.addMapper(boundType);
public class Configuration {
protected final MapperRegistry mapperRegistry = new MapperRegistry(this);
public <T> void addMapper(Class<T> type) {
/**
* mapperRegistry = {@link MapperRegistry} mapper接口註冊器，存放全部的mapper接口信息
*/
mapperRegistry.addMapper(type);
}
}
mapperRegistry.addMapper(type)；
爲Mapper接口建立一個代理工廠，方便後期使用Mapper接口時建立代理類
解析mapper接口的註解信息
public class MapperRegistry {
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 {
/**
* {@link MapperProxyFactory} 代理接口工廠
*/
knownMappers.put(type, new MapperProxyFactory<>(type));
// It's important that the type is added before the parser is run
// otherwise the binding may automatically be attempted by the
// mapper parser. If the type is already known, it won't try.
/**
* {@link MapperAnnotationBuilder} mapper接口註解解析器
*/
MapperAnnotationBuilder parser = new MapperAnnotationBuilder(config, type);
/* 開始解析 */
parser.parse();
loadCompleted = true;
} finally {
if (!loadCompleted) {
knownMappers.remove(type);
}
}
}
}
}
1.4.9 parser.parse(); MapperAnnotationBuilder.parse()
解析mapper接口的註解信息，parseStatement(method)主要在這個方法中完成
public class MapperAnnotationBuilder {
public void parse() {
String resource = type.toString();
if (!configuration.isResourceLoaded(resource)) {
loadXmlResource();
configuration.addLoadedResource(resource);
assistant.setCurrentNamespace(type.getName());
/**
* 解析 @CacheNamespace 註解
*/
parseCache();
/**
* 解析 CacheNamespaceRef 註解
*/
parseCacheRef();
Method[] methods = type.getMethods();
for (Method method : methods) {
try {
// issue #237
if (!method.isBridge()) {
/**
* 解析Sql相關注解 列如 @Select|@Update 之類的註解
*
* 重點關注
*/
parseStatement(method);
}
} catch (IncompleteElementException e) {
configuration.addIncompleteMethod(new MethodResolver(this, method));
}
}
}
/**
* 解析待定方法
*/
parsePendingMethods();
}
}
1.5.0：parseStatement(method)；
建立一個MappedStatement實例添加到 Configuration.mappedStatements的Map集合中
public class MapperAnnotationBuilder {
private final MapperBuilderAssistant assistant;
void parseStatement(Method method) {
/**
* 此處省略一大推代碼...
*/
assistant.addMappedStatement(
mappedStatementId,
sqlSource,
statementType,
sqlCommandType,
fetchSize,
timeout,
// ParameterMapID
null,
parameterTypeClass,
resultMapId,
getReturnType(method),
resultSetType,
flushCache,
useCache,
// TODO gcode issue #577
false,
keyGenerator,
keyProperty,
keyColumn,
// DatabaseID
null,
languageDriver,
// ResultSets
options != null ? nullOrEmpty(options.resultSets()) : null);
}
}
1.5.1：assistant.addMappedStatement();
這裏能夠參考1.4.6：builderAssistant.addMappedStatement();如出一轍的操做
都調用了configuration.addMappedStatement(statement);
這裏重點分析Configuration.addMappedStatement(statement);在作什麼操做，而且解決 1.4.2留下的疑點；UserMapper.xml和UserMapper接口都有findById的Sql語句定義
public class Configuration {
public void addMappedStatement(MappedStatement ms) {
mappedStatements.put(ms.getId(), ms);
}
}
mappedStatements.put(ms.getId(), ms); 實際調用 Configuration.StrictMap.put()方法
Configuration.StrictMap是一個重寫的HashMap，put方法會先校驗key是否存在
public class Configuration {
/**
* mappedStatements Sql語句的對象
*
* Configuration.StrictMap 實現了HashMap
*/
protected final Map<String, MappedStatement> mappedStatements = new Configuration.StrictMap<MappedStatement>("Mapped Statements collection")
.conflictMessageProducer((savedValue, targetValue) ->
". please check " + savedValue.getResource() + " and " + targetValue.getResource());
protected static class StrictMap<V> extends HashMap<String, V> {
@Override
@SuppressWarnings("unchecked")
public V put(String key, V value) {
/**
* key 是否存在 存在就拋出異常
*
* 由此得知，方法映射Sql語句只能定義一個，要麼在 mapper.xml中定義，要麼就註解定義
*/
if (containsKey(key)) {
throw new IllegalArgumentException(name + " already contains value for " + key
+ (conflictMessageProducer == null ? "" : conflictMessageProducer.apply(super.get(key), value)));
}
if (key.contains(".")) {
final String shortKey = getShortName(key);
if (super.get(shortKey) == null) {
super.put(shortKey, value);
} else {
super.put(shortKey, (V) new org.apache.ibatis.session.Configuration.StrictMap.Ambiguity(shortKey));
}
}
return super.put(key, value);
}
}
}
debug調試，key已經存在，就會報錯。由此得知，方法映射Sql語句只能定義一個，要麼在 mapper.xml中定義，要麼就註解定義
到此，MyBatis的啓動流程就走完了。
2：接下來就來看下是如何執行Sql查詢的。
public class Main {
public static void main(String[] args) throws IOException {
String configName = "mybatis_config.xml";
Reader reader = Resources.getResourceAsReader(configName);
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);
/**
* 獲取一個會話鏈接
*/
SqlSession sqlSession = sqlSessionFactory.openSession();
/**
* 拿到 UserMapper 的代理類
*/
UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
/**
* 執行Sql查詢
*/
User user = userMapper.findById(1);
System.out.println(user);
}
}
輸出結果：User{userId=1, username=‘張三’, sex=‘男’, age=12}
一行代碼的查詢，底層既然走了那麼多流程；
流程圖：
2.1：sqlSessionFactory.openSession();打開會話鏈接
調用DefaultSqlSessionFactory.openSessionFromDataSource();
public class DefaultSqlSessionFactory implements SqlSessionFactory {
private SqlSession openSessionFromDataSource(ExecutorType execType, TransactionIsolationLevel level, boolean autoCommit) {
Transaction tx = null;
try {
/**
* mybatis_config.xml配置的
* <environment>數據源<environment/>
*/
final Environment environment = configuration.getEnvironment();
/**
* transactionManager 配置的事務管理器工廠 type="JDBC" {@link JdbcTransactionFactory}
*<environments default="developmentss">
* <environment id="developmentss">
* <transactionManager type="JDBC"></transactionManager>
* </environment>
* </environments>
*/
final TransactionFactory transactionFactory = getTransactionFactoryFromEnvironment(environment);
/**
* 建立事務管理器，因爲上面指定的事務管理器工廠是 {@link JdbcTransactionFactory}
* 因此建立的事務管理器是 {@link JdbcTransaction}
*
* @param level 事務隔離級別
* @param autoCommit 是否自動提交事務
*/
tx = transactionFactory.newTransaction(environment.getDataSource(), level, autoCommit);
/**
* 建立Sql執行器
*
* @param execType 建立執行器類型 defaultExecutorType若是不指定 默認就是 SIMPLE
* <settings>
* <setting name="defaultExecutorType" value="SIMPLE"/>
* </settings>
*/
final Executor executor = configuration.newExecutor(tx, execType);
/**
* 建立一個默認的 SqlSession實例
*/
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();
}
}
}
2.2：configuration.newExecutor(tx, execType);建立執行器
public class Configuration {
public Executor newExecutor(Transaction transaction, ExecutorType executorType) {
executorType = executorType == null ? defaultExecutorType : executorType;
executorType = executorType == null ? ExecutorType.SIMPLE : executorType;
Executor executor;
if (ExecutorType.BATCH == executorType) {
/**
* 執行器不只重用語句還會執行批量更新
*/
executor = new BatchExecutor(this, transaction);
/**
* 執行器會重用預處理語句（PreparedStatement）
*/
} else if (ExecutorType.REUSE == executorType) {
executor = new ReuseExecutor(this, transaction);
} else {
/**
* 普通的執行器 也是默認的執行器
*/
executor = new SimpleExecutor(this, transaction);
}
/**
* 若是開啓了二級緩存 cacheEnabled，建立一個CachingExecutor緩存執行器
* cacheEnabled 默認爲true
* <settings>
* <setting name="cacheEnabled" value="true"/>
* </settings>
*/
if (cacheEnabled) {
executor = new CachingExecutor(executor);
}
executor = (Executor) interceptorChain.pluginAll(executor);
return executor;
}
}
2.3：sqlSession.getMapper(UserMapper.class);
獲取Mapper接口代理類實例
public class DefaultSqlSession implements SqlSession {
@Override
public <T> T getMapper(Class<T> type) {
/**
* 用 Configuration 類的 getMapper方法
*/
return configuration.getMapper(type, this);
}
}
public class Configuration {
public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
/**
* 調用 MapperRegistry Mapper接口註冊器
*/
return mapperRegistry.getMapper(type, sqlSession);
}
}
public class MapperRegistry {
private final Configuration config;
private final Map<Class<?>, MapperProxyFactory<?>> knownMappers = new HashMap<>();
public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
/**
* knownMappers 從緩存中獲取 MapperProxyFactory Mapper接口代理工廠
* 若是沒有找到就會拋出異常，
* 說明獲取Mapper接口代理實例時，須要事先定義好 --> 至關於Spring的掃包
*/
final MapperProxyFactory<T> mapperProxyFactory = (MapperProxyFactory<T>) knownMappers.get(type);
if (mapperProxyFactory == null) {
throw new BindingException("Type " + type + " is not known to the MapperRegistry.");
}
try {
/**
* 建立代理實例
*/
return mapperProxyFactory.newInstance(sqlSession);
} catch (Exception e) {
throw new BindingException("Error getting mapper instance. Cause: " + e, e);
}
}
}
2.3.1：使用JDK代理建立Mapper接口代理
InvocationHandler是MapperProxy
public class MapperProxyFactory<T> {
private final Class<T> mapperInterface;
/**
* MapperMethod 緩存
*/
private final Map<Method, MapperMethod> methodCache = new ConcurrentHashMap<>();
public MapperProxyFactory(Class<T> mapperInterface) {
this.mapperInterface = mapperInterface;
}
@SuppressWarnings("unchecked")
protected T newInstance(MapperProxy<T> mapperProxy) {
/**
* JDK 生產代理類
*/
return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(), new Class[] { mapperInterface }, mapperProxy);
}
public T newInstance(SqlSession sqlSession) {
/**
* 代理類回調接口
*/
final MapperProxy<T> mapperProxy = new MapperProxy<>(sqlSession, mapperInterface, methodCache);
return newInstance(mapperProxy);
}
}
2.4：userMapper.findById(1); 調用Mapper接口方法Sql查詢
會走代理類 MapperProxy.invoke
public class MapperProxy<T> implements InvocationHandler, Serializable {
private static final long serialVersionUID = -6424540398559729838L;
private final SqlSession sqlSession;
private final Class<T> mapperInterface;
private final Map<Method, MapperMethod> methodCache;
public MapperProxy(SqlSession sqlSession, Class<T> mapperInterface, Map<Method, MapperMethod> methodCache) {
this.sqlSession = sqlSession;
this.mapperInterface = mapperInterface;
this.methodCache = methodCache;
}
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
try {
if (Object.class.equals(method.getDeclaringClass())) {
return method.invoke(this, args);
} else if (method.isDefault()) {
return invokeDefaultMethod(proxy, method, args);
}
} catch (Throwable t) {
throw ExceptionUtil.unwrapThrowable(t);
}
/**
* 根據方法全限名 獲取一個MapperMethod實例，而且緩存
*
* 注意：這裏的 methodCache 只是一個引用，緩存的全部對象都在 {@link MapperProxyFactory#methodCache}中
*/
final MapperMethod mapperMethod = cachedMapperMethod(method);
/**
* 開始執行
*/
return mapperMethod.execute(sqlSession, args);
}
/**
* 添加到緩存 methodCache {@link MapperProxyFactory#methodCache}中
* computeIfAbsent HashMap 存在就獲取，不存在就新增
* @param method
* @return
*/
private MapperMethod cachedMapperMethod(Method method) {
return methodCache.computeIfAbsent(method, k -> new MapperMethod(mapperInterface, method, sqlSession.getConfiguration()));
}
}
2.5：mapperMethod.execute(sqlSession, args);
執行Sql語句查詢，因爲個人返回結果是一個 User對象，因此會走到
result = sqlSession.selectOne(command.getName(), param);這一行，查詢一條記錄
實際走到 DefaultSqlSession.selectOne()
public class MapperMethod {
private final org.apache.ibatis.binding.MapperMethod.SqlCommand command;
private final org.apache.ibatis.binding.MapperMethod.MethodSignature method;
public MapperMethod(Class<?> mapperInterface, Method method, Configuration config) {
this.command = new org.apache.ibatis.binding.MapperMethod.SqlCommand(config, mapperInterface, method);
this.method = new org.apache.ibatis.binding.MapperMethod.MethodSignature(config, mapperInterface, method);
}
/**
* 開始執行Sql查詢
*/
public Object execute(SqlSession sqlSession, Object[] args) {
Object result;
switch (command.getType()) {
case INSERT: {
// 省略代碼... 執行 insert語句 <insert>/@Insert
break;
}
case UPDATE: {
// 省略代碼... 執行 insert語句 <update>/@Update
break;
}
case DELETE: {
// 省略代碼... 執行 delete語句 <delete>/@Delete
break;
}
case SELECT: // 執行 select語句 <select>/@Select
if (method.returnsVoid() && method.hasResultHandler()) {
// 返回類型是否爲空 通常狀況作Sql操做都要有返回結果的
executeWithResultHandler(sqlSession, args);
result = null;
} else if (method.returnsMany()) {
/**
* 是否返回多個結果集 {@link Collection}集合/數組
*/
result = executeForMany(sqlSession, args);
} else if (method.returnsMap()) {
/**
* 返回類型是否爲 Map 集合
*/
result = executeForMap(sqlSession, args);
} else if (method.returnsCursor()) {
/**
* 返回類型是不是 遊標 {@link org.apache.ibatis.cursor.Cursor}
*/
result = executeForCursor(sqlSession, args);
} else {
/**
* 將參數轉換爲Sql命令參數
*/
Object param = method.convertArgsToSqlCommandParam(args);
/**
* 發起查詢 調用的是 sqlSession中的方法
*/
result = sqlSession.selectOne(command.getName(), param);
if (method.returnsOptional()
&& (result == null || !method.getReturnType().equals(result.getClass()))) {
result = Optional.ofNullable(result);
}
}
break;
case FLUSH: // 刷新
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;
}
}
DefaultSqlSession.selectOne()能夠看出實際是調用selectList()，並且若是返回了多個結果集就會報錯。錯誤信息以下
Expected one result (or null) to be returned by selectOne(), but found: 2
2.6：DefaultSqlSession.selectList()
查詢多結果集
public class DefaultSqlSession implements SqlSession {
/**
*
* @param statement 方法全限名 好比：com.mapper.UserMapper.findById
* @param parameter 參數
* @param rowBounds 分頁
* @param <E>
* @return
*/
@Override
public <E> List<E> selectList(String statement, Object parameter, RowBounds rowBounds) {
try {
/**
* 根據方法全限名在 configuration.mappedStatements緩存集合中拿到方法對應的Sql Statement對象實例
*/
MappedStatement ms = configuration.getMappedStatement(statement);
/**
* 使用執行器執行 由當前設置的執行器執行
* <setting name="defaultExecutorType" value="SIMPLE"/>
*
* <setting name="cacheEnabled" value="true"/>
* 注意：cacheEnabled因爲開啓二級緩存默認爲true，會先使用 {@link CachingExecutor} 緩存執行器查詢
*/
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();
}
}
}
2.7：executor.query執行器查詢
執行器的建立查看 2.2：configuration.newExecutor(tx, execType);建立執行器
/**
* 二級緩存執行器
*/
public class CachingExecutor implements Executor {
@Override
public <E> List<E> query(MappedStatement ms, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql)
throws SQLException {
/**
* 獲取指定的二級緩存
* mapper.xml 指定的 <cache type="com.domain.something.MyCustomCache"/>
* Mapper接口的 @CacheNamespace
*/
Cache cache = ms.getCache();
if (cache != null) {
/* 是否須要刷新二級緩存 */
flushCacheIfRequired(ms);
if (ms.isUseCache() && resultHandler == null) {
ensureNoOutParams(ms, boundSql);
@SuppressWarnings("unchecked")
/**
* 獲取二級緩存
*/
List<E> list = (List<E>) tcm.getObject(cache, key);
if (list == null) {
/**
* 若是沒有數據查詢Sql
*/
list = delegate.query(ms, parameterObject, rowBounds, resultHandler, key, boundSql);
/**
* 設置緩存
*/
tcm.putObject(cache, key, list); // issue #578 and #116
}
return list;
}
}
/**
* delegate = SimpleExecutor
*/
return delegate.query(ms, parameterObject, rowBounds, resultHandler, key, boundSql);
}
}
2.8：delegate.query(); delegate = SimpleExecutor
由於我沒有指定二級緩存，因此直接走向delegate.query, 由於SimpleExecutor繼承了BaseExecutor可是沒有重寫query方法，因此走的是BaseExecutor.query()
public abstract class BaseExecutor implements Executor {
@Override
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.");
}
/**
* 是否須要清空一級緩存 flushCache設置爲true生效
* <select flushCache="true"></select>
*/
if (queryStack == 0 && ms.isFlushCacheRequired()) {
clearLocalCache();
}
List<E> list;
try {
// 防止多線程重複調用處理
queryStack++;
/**
* localCache.getObject(key) 獲取一級緩存
* {@link BaseExecutor.localCache} 類型 org.apache.ibatis.cache.impl.PerpetualCache
*/
list = resultHandler == null ? (List<E>) localCache.getObject(key) : null;
if (list != null) {
handleLocallyCachedOutputParameters(ms, key, parameter, boundSql);
} else {
/**
* 發起數據庫查詢
*/
list = queryFromDatabase(ms, parameter, rowBounds, resultHandler, key, boundSql);
}
} finally {
queryStack--;
}
if (queryStack == 0) {
for (org.apache.ibatis.executor.BaseExecutor.DeferredLoad deferredLoad : deferredLoads) {
deferredLoad.load();
}
// issue #601
deferredLoads.clear();
if (configuration.getLocalCacheScope() == LocalCacheScope.STATEMENT) {
// issue #482
clearLocalCache();
}
}
return list;
}
}
2.9：queryFromDatabase()，
數據庫查詢 會執行到子類的doQuery()方法，這裏的字類是SimpleExecutor 因此執行 SimpleExecutor.doQuery()
public abstract class BaseExecutor implements Executor {
private <E> List<E> queryFromDatabase(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql) throws SQLException {
List<E> list;
/**
* 一級緩存佔位
*/
localCache.putObject(key, EXECUTION_PLACEHOLDER);
try {
/**
* 調用子類的 doQuery()方法
*
* 這裏的字類是SimpleExecutor 因此執行 SimpleExecutor.doQuery()
*/
list = doQuery(ms, parameter, rowBounds, resultHandler, boundSql);
} finally {
localCache.removeObject(key);
}
/**
* 添加一級緩存
*/
localCache.putObject(key, list);
if (ms.getStatementType() == StatementType.CALLABLE) {
localOutputParameterCache.putObject(key, parameter);
}
return list;
}
}
2.9.1：SimpleExecutor.doQuery()
執行數據庫查詢
public class SimpleExecutor extends BaseExecutor {
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();
/**
* 建立 RoutingStatementHandler Sql語句執行類型處理器
*/
StatementHandler handler = configuration.newStatementHandler(wrapper, ms, parameter, rowBounds, resultHandler, boundSql);
/**
* 建立 java.sql.Statement
*/
stmt = prepareStatement(handler, ms.getStatementLog());
/**
* 發起數據庫查詢
*/
return handler.query(stmt, resultHandler);
} finally {
closeStatement(stmt);
}
}
}
2.9.2：configuration.newStatementHandler();
建立 RoutingStatementHandler Sql語句執行類型處理器
public class RoutingStatementHandler implements StatementHandler {
private final StatementHandler delegate;
public RoutingStatementHandler(Executor executor, MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) {
switch (ms.getStatementType()) {
case STATEMENT:
/**
* 簡單的Sql執行處理器
*/
delegate = new SimpleStatementHandler(executor, ms, parameter, rowBounds, resultHandler, boundSql);
break;
case PREPARED:
/**
* 預編譯的Sql執行處理器
* 這是默認的
*/
delegate = new PreparedStatementHandler(executor, ms, parameter, rowBounds, resultHandler, boundSql);
break;
case CALLABLE:
/**
* 存儲過程執行的Sql執行處理器
*/
delegate = new CallableStatementHandler(executor, ms, parameter, rowBounds, resultHandler, boundSql);
break;
default:
throw new ExecutorException("Unknown statement type: " + ms.getStatementType());
}
}
}
2.9.3：prepareStatement()
建立 java.sql.Statement
private Statement prepareStatement(StatementHandler handler, Log statementLog) throws SQLException {
Statement stmt;
Connection connection = getConnection(statementLog);
stmt = handler.prepare(connection, transaction.getTimeout());
handler.parameterize(stmt);
return stmt;
}
3.0：handler.query(stmt, resultHandler);
delegate 參考2.9.2：configuration.newStatementHandler()
public class RoutingStatementHandler implements StatementHandler {
private final StatementHandler delegate;
@Override
public <E> List<E> query(Statement statement, ResultHandler resultHandler) throws SQLException {
/**
* 當前的 delegate = PreparedStatementHandler
*/
return delegate.query(statement, resultHandler);
}
}
3.1：delegate.query(statement, resultHandler);
執行 PreparedStatementHandler.query()
public class PreparedStatementHandler extends BaseStatementHandler {
@Override
public <E> List<E> query(Statement statement, ResultHandler resultHandler) throws SQLException {
PreparedStatement ps = (PreparedStatement) statement;
/**
* 發起數據庫查詢
*/
ps.execute();
/**
* 封裝結果集 resultSetHandler = DefaultResultSetHandler
*/
return resultSetHandler.handleResultSets(ps);
}
}
3.2：resultSetHandler.handleResultSets(ps);
封裝結果集
public class DefaultResultSetHandler implements ResultSetHandler {
/**
* 封裝結果集
* @param stmt
* @return
* @throws SQLException
*/
@Override
public List<Object> handleResultSets(Statement stmt) throws SQLException {
ErrorContext.instance().activity("handling results").object(mappedStatement.getId());
final List<Object> multipleResults = new ArrayList<>();
int resultSetCount = 0;
/**
* 包裝 ResultSet
*/
ResultSetWrapper rsw = getFirstResultSet(stmt);
List<ResultMap> resultMaps = mappedStatement.getResultMaps();
int resultMapCount = resultMaps.size();
validateResultMapsCount(rsw, resultMapCount);
while (rsw != null && resultMapCount > resultSetCount) {
ResultMap resultMap = resultMaps.get(resultSetCount);
handleResultSet(rsw, resultMap, multipleResults, null);
rsw = getNextResultSet(stmt);
cleanUpAfterHandlingResultSet();
resultSetCount++;
}
String[] resultSets = mappedStatement.getResultSets();
if (resultSets != null) {
while (rsw != null && resultSetCount < resultSets.length) {
ResultMapping parentMapping = nextResultMaps.get(resultSets[resultSetCount]);
if (parentMapping != null) {
String nestedResultMapId = parentMapping.getNestedResultMapId();
ResultMap resultMap = configuration.getResultMap(nestedResultMapId);
handleResultSet(rsw, resultMap, null, parentMapping);
}
rsw = getNextResultSet(stmt);
cleanUpAfterHandlingResultSet();
resultSetCount++;
}
}
/**
* 包裝成 List
*/
return collapseSingleResultList(multipleResults);
}
}
到這裏MyBatis的Sql查詢就結束了，同理添加，修改，刪除也是一樣的流程。
能夠本身跟着以上步驟，斷點調試追蹤下源碼，一切迷霧都將會撥開的。
總結：
- 核心依賴於動態代理模式建立Mapper接口代理實例
- SqlSessionFactory負責建立SqlSession，全局惟一實例(相似於單例)
- Configuration 核心中的核心，走到哪裏都有它的存在，並且是全局惟一實例(相似於單例)
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