以下SQL的执行为例，描述mybatis的SQL执行过程
public DataResponse
mybatis SQL首先通过JDK动态代理调用MapperProxy的invoke方法
public class MapperProxyimplements InvocationHandler, Serializable { @Override public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { try { if (Object.class.equals(method.getDeclaringClass())) { // Objec代理的方法执行 return method.invoke(this, args); } else { // 执行方法调用，一般都从这里开始调用 return cachedInvoker(method).invoke(proxy, method, args, sqlSession); } } catch (Throwable t) { throw ExceptionUtil.unwrapThrowable(t); } } @Override public Object invoke(Object proxy, Method method, Object[] args, SqlSession sqlSession) throws Throwable { return mapperMethod.execute(sqlSession, args); } }
mapperMethod.execute调用MapperMethod#execute，该方法根据不同的command.getType()，执行不同的SQL
public class MapperMethod {
public Object execute(SqlSession sqlSession, Object[] args) {
Object result;
switch (command.getType()) {
case INSERT: { // 插入
Object param = method.convertArgsToSqlCommandParam(args);
result = rowCountResult(sqlSession.insert(command.getName(), param));
break;
}
case UPDATe: { // 更新
Object param = method.convertArgsToSqlCommandParam(args);
result = rowCountResult(sqlSession.update(command.getName(), param));
break;
}
case DELETE: { // 删除
Object param = method.convertArgsToSqlCommandParam(args);
result = rowCountResult(sqlSession.delete(command.getName(), param));
break;
}
case SELECT: // 查询
if (method.returnsVoid() && method.hasResultHandler()) { // 查询结果返回空并且有返回结果需要处理的情况
executeWithResultHandler(sqlSession, args);
result = null;
} else if (method.returnsMany()) { // 查询结果返回多条
result = executeForMany(sqlSession, args);
} else if (method.returnsMap()) { // 查询结果返回Map
result = executeForMap(sqlSession, args);
} else if (method.returnsCursor()) { // 查询结果返回游标
result = executeForCursor(sqlSession, args);
} else { // 查询结果返回单条记录
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: // 刷新Statements
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;
}
}
executeForMany(sqlSession, args)方法首先将参数转化为SQL命令参数，然后使用sqlSession执行selectList
privateObject executeForMany(SqlSession sqlSession, Object[] args) { List result; //将参数转化为SQL命令参数 Object param = method.convertArgsToSqlCommandParam(args); if (method.hasRowBounds()) { RowBounds rowBounds = method.extractRowBounds(args); result = sqlSession.selectList(command.getName(), param, rowBounds); } else { // 执行selectList result = sqlSession.selectList(command.getName(), param); } // issue #510 Collections & arrays support if (!method.getReturnType().isAssignableFrom(result.getClass())) { if (method.getReturnType().isArray()) { return convertToArray(result); } else { return convertToDeclaredCollection(sqlSession.getConfiguration(), result); } } return result; }
sqlSession.selectList(command.getName(), param)方法会调用SqlSessionTemplate#selectList, 该方法调用代理
public class SqlSessionTemplate implements SqlSession, DisposableBean {
public List selectList(String statement, Object parameter) {
// 调用到invoke方法
return this.sqlSessionProxy.selectList(statement, parameter);
}
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
// 获取SqlSession
SqlSession sqlSession = getSqlSession(SqlSessionTemplate.this.sqlSessionFactory,
SqlSessionTemplate.this.executorType, SqlSessionTemplate.this.exceptionTranslator);
try {
// 调用方法
Object result = method.invoke(sqlSession, args);
if (!isSqlSessionTransactional(sqlSession, SqlSessionTemplate.this.sqlSessionFactory)) { // 带事务时强制提交/回滚
// force commit even on non-dirty sessions because some databases require
// a commit/rollback before calling close()
sqlSession.commit(true);
}
return result;
} catch (Throwable t) {
Throwable unwrapped = unwrapThrowable(t);
if (SqlSessionTemplate.this.exceptionTranslator != null && unwrapped instanceof PersistenceException) {
// release the connection to avoid a deadlock if the translator is no loaded. See issue #22
closeSqlSession(sqlSession, SqlSessionTemplate.this.sqlSessionFactory);
sqlSession = null;
Throwable translated = SqlSessionTemplate.this.exceptionTranslator
.translateExceptionIfPossible((PersistenceException) unwrapped);
if (translated != null) {
unwrapped = translated;
}
}
throw unwrapped;
} finally {
if (sqlSession != null) {
closeSqlSession(sqlSession, SqlSessionTemplate.this.sqlSessionFactory);
}
}
}
}
}
method.invoke(sqlSession, args)会调用到DefaultSqlSession#selectList，selectList获取映射的Statements, 然后使用executor去执行查询
public class DefaultSqlSession implements SqlSession {
@Override
public List selectList(String statement, Object parameter, RowBounds rowBounds) {
try {
// 获取映射的Statements
MappedStatement ms = configuration.getMappedStatement(statement);
// 使用executor去执行查询
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();
}
}
}
获取映射的Statements调用了Configuration#getMappedStatement，该方法会从statements Map中根据id获取对应的statement，statements Map中的值在应用启动时，mybatis会加载
public class Configuration {
public MappedStatement getMappedStatement(String id) {
return this.getMappedStatement(id, true);
}
public MappedStatement getMappedStatement(String id, boolean validateIncompleteStatements) {
if (validateIncompleteStatements) {
buildAllStatements();
}
return mappedStatements.get(id);
}
}
executor.query(ms, wrapCollection(parameter), rowBounds, Executor.NO_RESULT_HANDLER)方法执行前会调用插件代理Plugin#invoke， 如常用的分页插件等
public class Plugin implements InvocationHandler {
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
try {
// 获取方法集合
Set methods = signatureMap.get(method.getDeclaringClass());
if (methods != null && methods.contains(method)) {
// 执行拦截器
return interceptor.intercept(new Invocation(target, method, args));
}
return method.invoke(target, args);
} catch (Exception e) {
throw ExceptionUtil.unwrapThrowable(e);
}
}
}
这里使用了PageHelper，他会拦截查询语句，先查出总的数据数，然后在查具体数据
public class PageInterceptor implements Interceptor {
@Override
public Object intercept(Invocation invocation) throws Throwable {
try {
Object[] args = invocation.getArgs();
MappedStatement ms = (MappedStatement) args[0];
Object parameter = args[1];
RowBounds rowBounds = (RowBounds) args[2];
ResultHandler resultHandler = (ResultHandler) args[3];
Executor executor = (Executor) invocation.getTarget();
CacheKey cacheKey;
BoundSql boundSql;
//由于逻辑关系，只会进入一次
if (args.length == 4) {
//4 个参数时
boundSql = ms.getBoundSql(parameter);
// 创建缓存的key
cacheKey = executor.createCacheKey(ms, parameter, rowBounds, boundSql);
} else {
//6 个参数时
cacheKey = (CacheKey) args[4];
boundSql = (BoundSql) args[5];
}
// 检查对话是否存在
checkDialectExists();
//对 boundSql 的拦截处理
if (dialect instanceof BoundSqlInterceptor.Chain) {
// 绑定sql
boundSql = ((BoundSqlInterceptor.Chain) dialect).doBoundSql(BoundSqlInterceptor.Type.ORIGINAL, boundSql, cacheKey);
}
List resultList;
//调用方法判断是否需要进行分页，如果不需要，直接返回结果
if (!dialect.skip(ms, parameter, rowBounds)) {
//判断是否需要进行 count 查询
if (dialect.beforeCount(ms, parameter, rowBounds)) {
//动态拼接SQL，查询数据总数
Long count = count(executor, ms, parameter, rowBounds, null, boundSql);
// 处理查询总数，返回 true 时继续分页查询，false 时直接返回
if (!dialect.afterCount(count, parameter, rowBounds)) {
//当查询总数为 0 时，直接返回空的结果
return dialect.afterPage(new ArrayList(), parameter, rowBounds);
}
}
// 查询数据列表
resultList = ExecutorUtil.pageQuery(dialect, executor, ms, parameter, rowBounds, resultHandler, boundSql, cacheKey);
} else {
//rowBounds用参数值，不使用分页插件处理时，仍然支持默认的内存分页
resultList = executor.query(ms, parameter, rowBounds, resultHandler, cacheKey, boundSql);
}
return dialect.afterPage(resultList, parameter, rowBounds);
} finally {
if(dialect != null){
dialect.afterAll();
}
}
}
}
分页查询数据调用ExecutorUtil#pageQuery
public abstract class ExecutorUtil {
public static List pageQuery(Dialect dialect, Executor executor, MappedStatement ms, Object parameter,
RowBounds rowBounds, ResultHandler resultHandler,
BoundSql boundSql, CacheKey cacheKey) throws SQLException {
//判断是否需要进行分页查询
if (dialect.beforePage(ms, parameter, rowBounds)) {
//生成分页的缓存 key
CacheKey pageKey = cacheKey;
//处理参数对象
parameter = dialect.processParameterObject(ms, parameter, boundSql, pageKey);
//调用方言获取分页 sql
String pageSql = dialect.getPageSql(ms, boundSql, parameter, rowBounds, pageKey);
BoundSql pageBoundSql = new BoundSql(ms.getConfiguration(), pageSql, boundSql.getParameterMappings(), parameter);
Map additionalParameters = getAdditionalParameter(boundSql);
//设置动态参数
for (String key : additionalParameters.keySet()) {
pageBoundSql.setAdditionalParameter(key, additionalParameters.get(key));
}
//对 boundSql 的拦截处理
if (dialect instanceof BoundSqlInterceptor.Chain) {
pageBoundSql = ((BoundSqlInterceptor.Chain) dialect).doBoundSql(BoundSqlInterceptor.Type.PAGE_SQL, pageBoundSql, pageKey);
}
//执行分页查询
return executor.query(ms, parameter, RowBounds.DEFAULT, resultHandler, pageKey, pageBoundSql);
} else {
//不执行分页的情况下，也不执行内存分页
return executor.query(ms, parameter, RowBounds.DEFAULT, resultHandler, cacheKey, boundSql);
}
}
executor.query(ms, parameter, RowBounds.DEFAULT, resultHandler, pageKey, pageBoundSql)会调用CachingExecutor#query方法
public class CachingExecutor implements Executor {
public List query(MappedStatement ms, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql)
throws SQLException {
Cache cache = ms.getCache();
if (cache != null) { // 缓存存在，从缓存里面取
flushCacheIfRequired(ms);
if (ms.isUseCache() && resultHandler == null) {
ensureNoOutParams(ms, boundSql);
@SuppressWarnings("unchecked")
List list = (List) tcm.getObject(cache, key);
if (list == null) { // 缓存不存在，查询数据库
list = delegate.query(ms, parameterObject, rowBounds, resultHandler, key, boundSql);
tcm.putObject(cache, key, list); // issue #578 and #116
}
return list; // 缓存存在，直接返回
}
}
// 执行查询
return delegate.query(ms, parameterObject, rowBounds, resultHandler, key, boundSql);
}
}
delegate.query(ms, parameterObject, rowBounds, resultHandler, key, boundSql)会调用Executor#query方法，优先取缓存的值，如果缓存没有，再查询数据库
public abstract class baseExecutor implements Executor {
@Override
public List 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()) {
clearLocalCache();
}
List list;
try {
queryStack++;
// 获取缓存值
list = resultHandler == null ? (List) localCache.getObject(key) : null;
if (list != null) { // 缓存有值
handleLocallyCachedOutputParameters(ms, key, parameter, boundSql);
} else { // 缓存没有值，查询数据库
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;
}
// 从数据库查询数据
private List queryFromDatabase(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql) throws SQLException {
List list;
// 设置本次查询缓存占位符
localCache.putObject(key, EXECUTION_PLACEHOLDER);
try {
// 查询数据
list = doQuery(ms, parameter, rowBounds, resultHandler, boundSql);
} finally {
// 删除缓存
localCache.removeObject(key);
}
// 更新缓存
localCache.putObject(key, list);
if (ms.getStatementType() == StatementType.CALLABLE) {
localOutputParameterCache.putObject(key, parameter);
}
return list;
}
}
doQuery(ms, parameter, rowBounds, resultHandler, boundSql)会根据配置调用实现了baseExecutor的子类，子类有：BatchExecutor、ClosedExecutor、ResueExecutor和SimpleExecutor
一般使用的是SimpleExecutor, 他的doQuery方法如下
public class SimpleExecutor extends baseExecutor {
public List doQuery(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) throws SQLException {
Statement stmt = null;
try {
// 获取配置
Configuration configuration = ms.getConfiguration();
// 生成StatementHandler
StatementHandler handler = configuration.newStatementHandler(wrapper, ms, parameter, rowBounds, resultHandler, boundSql);
// 预处理Statement
stmt = prepareStatement(handler, ms.getStatementLog());
// 执行查询
return handler.query(stmt, resultHandler);
} finally {
closeStatement(stmt);
}
}
}
handler.query(stmt, resultHandler)首先调用RoutingStatementHandler#query，这里会代理到PreparedStatementHandler#query
public class RoutingStatementHandler implements StatementHandler {
@Override
public List query(Statement statement, ResultHandler resultHandler) throws SQLException {
return delegate.query(statement, resultHandler);
}
}
public class PreparedStatementHandler extends baseStatementHandler {
@Override
public List query(Statement statement, ResultHandler resultHandler) throws SQLException {
// 转化为PreparedStatement
PreparedStatement ps = (PreparedStatement) statement;
// 执行sql
ps.execute();
// 处理结果集
return resultSetHandler.handleResultSets(ps);
}
}
ps.execute()会调用到DruidPooledPreparedStatement#execute
public class DruidPooledPreparedStatement extends DruidPooledStatement implements PreparedStatement {
@Override
public boolean execute() throws SQLException {
// 开启检查
checkOpen();
// 增加执行计数器
incrementExecuteCount();
// 事务记录
transactionRecord(sql);
// 执行之前处理
conn.beforeExecute();
try {
// 执行SQL
return stmt.execute();
} catch (Throwable t) {
errorCheck(t);
throw checkException(t);
} finally {
// 执行之后处理
conn.afterExecute();
}
}
}
resultSetHandler.handleResultSets处理执行的结果时会调用结果集处理器DefaultResultSetHandler#handleResultSets
public class DefaultResultSetHandler implements ResultSetHandler {
@Override
public List
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