Mybatis源碼解讀
1 源碼下載
學(xué)習(xí)源碼之前需要先將源碼下載下來，這里需要下載mybatis源碼和mybatis-parent源碼，下載地址如下：
下載mybatis源碼時選擇對應(yīng)的Release版本：
下載完mybatis源碼之后，將其導(dǎo)入到IDEA中，注意pom.xml中的依賴版本
<parent>
<groupId>org.mybatis</groupId>
<artifactId>mybatis-parent</artifactId>
<version>32</version>
<relativePath>../parent-mybatis-parent-32/pom.xml</relativePath>
</parent>
其中關(guān)注version為32，relativePath為編譯后的mybatis-parent中pom.xml文件的相對路徑。從https://github.com/mybatis/parent下載對應(yīng)版本的依賴
下載之后，解壓先編譯mybatis-parent-32在編譯mybatis
編譯mybatis-parent-32：進(jìn)入目錄執(zhí)行
mvn clean install -Dmaven.test.skip
編譯mybatis：進(jìn)入目錄執(zhí)行
mvn clean install -Dmaven.test.skip
顯示BUILD SUCCESS表示導(dǎo)入成功，就可以閱讀源碼了。
2 源碼解讀
我們知道m(xù)ybatis是一款在持久層使用的框架，其內(nèi)部封裝了JDBC的操作，首先看看JDBC操作數(shù)據(jù)庫的過程
package cn.jdbc;
import java.sql.*;
public class jdbcTest { //定義測試類
public static void main(String[] args) {
Connection conn = null;
PreparedStatement pstmt = null;
ResultSet rs = null;
try {
String driver = "com.mysql.jdbc.Driver";//1.定義driverClass
String url = "jdbc:mysql://localhost:3306/test"; //2.定義url
String username = "root"; //3.定義用戶名，寫你想要連接到的用戶。
String password = "123456"; //4.用戶密碼。
String sql = "select * from user"; //5.你想要查找的表名。
Class.forName(driver);//6.注冊驅(qū)動程序
conn = DriverManager.getConnection(url, username, password);//7.獲取數(shù)據(jù)庫連接
//Statement stmt=conn.createStatement(); //8.構(gòu)造一個statement對象來執(zhí)行sql語句
pstmt = conn.prepareStatement(sql);
//CallableStatement cstmt = conn.prepareCall("{CALL demoSp(? , ?)}") ;
rs = pstmt.executeQuery();//9.執(zhí)行sql
while (rs.next()) { //10.遍歷結(jié)果集
//do something...
}
} catch (Exception e) {
e.printStackTrace();
} finally {
if (rs != null) {//11.關(guān)閉記錄集
try {
rs.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
if (pstmt != null) {//12.關(guān)閉聲明的對象
try {
pstmt.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
if (conn != null) {//13.關(guān)閉連接
try {
conn.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
}
}
}
以上流程大致分為四步分別是獲取連接對象、執(zhí)行sql語句、處理結(jié)果集、關(guān)閉連接
mybatis源碼也為我們封裝了這四步
2.1 獲取連接對象
首先看看mybatis官方入門文檔，需要創(chuàng)建一個xml文件，并且定義數(shù)據(jù)源DataSource以及事務(wù)管理器TransactionFactory，然后通過加載解析xml文件生成Configuration，下面給出xml文件的簡單示例：
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
<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>
<mappers>
<mapper resource="org/mybatis/example/BlogMapper.xml"/>
</mappers>
</configuration>
其中environment包含數(shù)據(jù)源和事務(wù)管理器，mapper有三個屬性分別是resource、class、url
resource表示Mapper.xml文件的資源路徑
class表示Mapper接口的路徑，這里搜索Mapper.xml文件默認(rèn)從Mapper接口下查找
url路徑對應(yīng)的是網(wǎng)絡(luò)上了某個文件，注意file:// 前綴 +路徑+文件名
當(dāng)然也可以使用package表示指定包下的所有Mapper
mybatis主要通過SqlSession操作數(shù)據(jù)的，對于SqlSession的獲取首先需要構(gòu)建一個SqlSessionFactory工廠，其代碼如下：
String resource = "org/mybatis/example/mybatis-config.xml";
InputStream inputStream = Resources.getResourceAsStream(resource);
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
跟蹤build方法發(fā)現(xiàn)最終執(zhí)行
//最終執(zhí)行此方法 reader輸入流，environment環(huán)境，properties配置文件
public SqlSessionFactory build(Reader reader, String environment, Properties properties) {
try {
XMLConfigBuilder parser = new XMLConfigBuilder(reader, environment, properties); return build(parser.parse());
} catch (Exception e) {
throw ExceptionFactory.wrapException("Error building SqlSession.", e);
} finally {
ErrorContext.instance().reset();
try {
reader.close();
} catch (IOException e) {
// Intentionally ignore. Prefer previous error.
}
}
}
其中XMLConfigBuilder中的parser方法跟蹤如下：
//解析Configuration文件
private void parseConfiguration(XNode root) {
try {
// issue #117 read properties first
//配置文件
propertiesElement(root.evalNode("properties"));
Properties settings = settingsAsProperties(root.evalNode("settings"));
loadCustomVfs(settings);
loadCustomLogImpl(settings);
//配置別名
typeAliasesElement(root.evalNode("typeAliases"));
//插件
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
//環(huán)境 1.DataSource 2.TransactionFactory
environmentsElement(root.evalNode("environments"));
databaseIdProviderElement(root.evalNode("databaseIdProvider"));
typeHandlerElement(root.evalNode("typeHandlers"));
//解析mapper
mapperElement(root.evalNode("mappers"));
} catch (Exception e) {
throw new BuilderException("Error parsing SQL Mapper Configuration. Cause: " + e, e);
}
}
這里重點注意的是解析mapper，在Configuration中的MapperRegistry中添加mapper具體如下：
//在MapperRegistry中添加一個Mapper
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 {
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.
MapperAnnotationBuilder parser = new MapperAnnotationBuilder(config, type);
parser.parse();
loadCompleted = true;
} finally {
if (!loadCompleted) {
knownMappers.remove(type);
}
}
}
}
其中knownMappers的定義如下：
private final Map<Class<?>, MapperProxyFactory<?>> knownMappers = new HashMap<>();
是一個map，map的key是Mapper的類型，value是Mapper的代理工廠MapperProxyFactory，使用該工廠動態(tài)代理出Mapper，MapperProxyFactory定義一個map：
private final Map<Method, MapperMethodInvoker> methodCache = new ConcurrentHashMap<>();
key是Method，value是MapperMethodInvoker，它是MapperProxy類的內(nèi)部接口。
使用MapperAnnotationBuilder解析Mapper
//解析mapper
public void parse() {
String resource = type.toString();
if (!configuration.isResourceLoaded(resource)) {
//加載xml文件
loadXmlResource();
configuration.addLoadedResource(resource);
assistant.setCurrentNamespace(type.getName());
parseCache();
parseCacheRef();
for (Method method : type.getMethods()) {
if (!canHaveStatement(method)) {
continue;
}
if (getAnnotationWrapper(method, false, Select.class, SelectProvider.class).isPresent()
&& method.getAnnotation(ResultMap.class) == null) {
//構(gòu)建resultMap
parseResultMap(method);
}
try {
//構(gòu)建sql
parseStatement(method);
} catch (IncompleteElementException e) {
configuration.addIncompleteMethod(new MethodResolver(this, method));
}
}
}
parsePendingMethods();
}
這里主要關(guān)心構(gòu)建sql過程，跟蹤parseStatement方法
void parseStatement(Method method) {
final Class<?> parameterTypeClass = getParameterType(method);
final LanguageDriver languageDriver = getLanguageDriver(method);
getAnnotationWrapper(method, true, statementAnnotationTypes).ifPresent(statementAnnotation -> {
//構(gòu)建SqlSource
final SqlSource sqlSource = buildSqlSource(statementAnnotation.getAnnotation(), parameterTypeClass, languageDriver, method);
final SqlCommandType sqlCommandType = statementAnnotation.getSqlCommandType();
final Options options = getAnnotationWrapper(method, false, Options.class).map(x -> (Options)x.getAnnotation()).orElse(null);
final String mappedStatementId = type.getName() + "." + method.getName();
final KeyGenerator keyGenerator;
String keyProperty = null;
String keyColumn = null;
if (SqlCommandType.INSERT.equals(sqlCommandType) || SqlCommandType.UPDATE.equals(sqlCommandType)) {
// first check for SelectKey annotation - that overrides everything else
SelectKey selectKey = getAnnotationWrapper(method, false, SelectKey.class).map(x -> (SelectKey)x.getAnnotation()).orElse(null);
if (selectKey != null) {
keyGenerator = handleSelectKeyAnnotation(selectKey, mappedStatementId, getParameterType(method), languageDriver);
keyProperty = selectKey.keyProperty();
} else if (options == null) {
keyGenerator = configuration.isUseGeneratedKeys() ? Jdbc3KeyGenerator.INSTANCE : NoKeyGenerator.INSTANCE;
} else {
keyGenerator = options.useGeneratedKeys() ? Jdbc3KeyGenerator.INSTANCE : NoKeyGenerator.INSTANCE;
keyProperty = options.keyProperty();
keyColumn = options.keyColumn();
}
} else {
keyGenerator = NoKeyGenerator.INSTANCE;
}
Integer fetchSize = null;
Integer timeout = null;
StatementType statementType = StatementType.PREPARED;
ResultSetType resultSetType = configuration.getDefaultResultSetType();
boolean isSelect = sqlCommandType == SqlCommandType.SELECT;
boolean flushCache = !isSelect;
boolean useCache = isSelect;
if (options != null) {
if (FlushCachePolicy.TRUE.equals(options.flushCache())) {
flushCache = true;
} else if (FlushCachePolicy.FALSE.equals(options.flushCache())) {
flushCache = false;
}
useCache = options.useCache();
fetchSize = options.fetchSize() > -1 || options.fetchSize() == Integer.MIN_VALUE ? options.fetchSize() : null; //issue #348
timeout = options.timeout() > -1 ? options.timeout() : null;
statementType = options.statementType();
if (options.resultSetType() != ResultSetType.DEFAULT) {
resultSetType = options.resultSetType();
}
}
String resultMapId = null;
if (isSelect) {
ResultMap resultMapAnnotation = method.getAnnotation(ResultMap.class);
if (resultMapAnnotation != null) {
resultMapId = String.join(",", resultMapAnnotation.value());
} else {
resultMapId = generateResultMapName(method);
}
}
//構(gòu)建MappedStatement
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,
statementAnnotation.getDatabaseId(),
languageDriver,
// ResultSets
options != null ? nullOrEmpty(options.resultSets()) : null);
});
}
進(jìn)入buildSqlSource方法查看解析sql的過程
//主要解析sql的方法
public String parse(String text) {
if (text == null || text.isEmpty()) {
return "";
}
// search open token
int start = text.indexOf(openToken);
if (start == -1) {
//找不到說明沒有參數(shù)
return text;
}
//有參數(shù)，將字符串轉(zhuǎn)化為數(shù)組進(jìn)行操作
char[] src = text.toCharArray();
int offset = 0;
//保留字符串構(gòu)建器
final StringBuilder builder = new StringBuilder();
//表達(dá)式這里存儲#{}或者${}括號中間的
StringBuilder expression = null;
do {
if (start > 0 && src[start - 1] == '\\') {
// this open token is escaped. remove the backslash and continue.
// \\${}或者\\#{}這時表示字符串"\${}"或者"\#{}"
// select * from user where id=\\#{id} => select * from user where id=#{id}
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);
}
//將openToken之間的拷貝到builder中
builder.append(src, offset, start - offset);
//偏移openToken.length個長度
offset = start + openToken.length();
//從偏移開始找closeToken位置
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.
// 若是\\}情況則跳過，繼續(xù)找下一個}
expression.append(src, offset, end - offset - 1).append(closeToken);
offset = end + closeToken.length();
end = text.indexOf(closeToken, offset);
} else {
//expression存儲openToken和closeToken之間的字符
//找到了closeToken直接跳出循環(huán)
expression.append(src, offset, end - offset);
break;
}
}
//走到這里 1.找不到closeToken 這里end=-1 后面的全部填上
if (end == -1) {
// close token was not found.
builder.append(src, start, src.length - start);
offset = src.length;
} else {
//有openToken和closeToken 將其替換成? 并且將參數(shù)設(shè)置到Handler中
builder.append(handler.handleToken(expression.toString()));
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();
}
執(zhí)行完畢后Configuration對象構(gòu)造成功，返回DefaultSqlSessionFactory，通過openSession方法獲得SqlSession對象。
2.2 執(zhí)行sql語句
生成Mapper代理對象過程如下
DefaultSqlSession--->Configuration--->MapperRegistry--->MapperProxyFactory
獲取代理對象之后執(zhí)行方法時會自動調(diào)用MapperProxy中的invoke方法，跟蹤
//執(zhí)行主入口，根據(jù)sql類型執(zhí)行相應(yīng)的分支
public Object execute(SqlSession sqlSession, Object[] args) {
Object result;
switch (command.getType()) {
//新增邏輯
case INSERT: {
//將args對象數(shù)組，轉(zhuǎn)換成sql參數(shù)
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()) {
//返回值是list
result = executeForMany(sqlSession, args);
} else if (method.returnsMap()) {
result = executeForMap(sqlSession, args);
} else if (method.returnsCursor()) {
result = executeForCursor(sqlSession, args);
} else {
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;
}
其中Insert、Update、Delete的返回結(jié)果都是int或者long 其表示操作影響行數(shù)，而Select的返回結(jié)果有
Void、many、one、map、cursor，下面分析Select過程
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.");
}
if (queryStack == 0 && ms.isFlushCacheRequired()) {
//queryStack緩存棧指針為0 且可以清空緩存 則清空緩存
clearLocalCache();
}
List<E> list;
try {
queryStack++;
list = resultHandler == null ? (List<E>) localCache.getObject(key) : null;
if (list != null) {
handleLocallyCachedOutputParameters(ms, key, parameter, boundSql);
} else {
//從數(shù)據(jù)庫查數(shù)據(jù)
list = queryFromDatabase(ms, parameter, rowBounds, resultHandler, key, boundSql);
}
} finally {
queryStack--;
}
if (queryStack == 0) {
for (DeferredLoad deferredLoad : deferredLoads) {
deferredLoad.load();
}
// issue #601
deferredLoads.clear();
if (configuration.getLocalCacheScope() == LocalCacheScope.STATEMENT) {
// issue #482
clearLocalCache();
}
}
return list;
}
其中有緩存直接從緩存中拿，沒有緩存則從數(shù)據(jù)庫查
執(zhí)行器的繼承結(jié)構(gòu)如下：
最終在相應(yīng)的Executor執(zhí)行相應(yīng)的邏輯，以query為例
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);
}
}
下面是StatementHandler的繼承結(jié)構(gòu)
其中PreparedStatementHandler、SimpleStatementHandler、CallableStatementhandler分別對應(yīng)Statement接口中的PreparedStatement、Statement、CallableStatement
2.3 處理結(jié)果集
進(jìn)入query方法處理結(jié)果集
//處理結(jié)果集
@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;
//獲取結(jié)果集，并將其包裝成ResultSetWrapper對象
ResultSetWrapper rsw = getFirstResultSet(stmt);
//獲取定義的resultMap
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++;
}
}
return collapseSingleResultList(multipleResults);
}
