mybatis原始碼解讀---一條sql的旅程

select user_id as userId,user_name userName,age from op_user_info where user_id>#{userId}
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<configuration> 
  <dataSource type="POOLED">
    <property name="driver" value="${driver}"/>
    <property name="url" value="${url}"/>
    <property name="username" value="${username}"/>
    <property name="password" value="${password}"/>
  </dataSource>
  <mappers>
     <mapper class="classpath*:mybatis/UserMapper.xml"/>
  </mappers>
   ....
</configuration>  
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<mapper namespace="com.alibaba.test.UserDao">
     <select id="getUser" parameterType="com.alibaba.test.UserBO"
            resultType="com.alibaba.test.UserDO">
   select user_id as userId,user_name userName,age from op_user_info where user_id>#{userId}
      </select>
     ......
</mapper>
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public interface UserDao {
    public UserDO getUser(UserBO UserBO)
    .......
}
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SqlSession sqlSession = sqlSessionFactory.openSession();
try {
  UserBO  userBO= new UserBO();
  userBO.setUserId(148736);
  UserDO user = (UserDO) sqlSession.select("com.alibaba.test.UserDao.getUser", userBO);
} finally {
  session.close();
}
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SqlSession session = sqlSessionFactory.openSession();
try {
  UserBO  userBO= new UserBO();
  userBO.setUserId(148736);
  UserDao userDao = session.getMapper(UserDao.class);
  UserDO user    userDao.getUser(userBO);
} finally {
session.close();
}
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public class MapperProxy<T> implements InvocationHandler, Serializable {
  @Override
  public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
    if (Object.class.equals(method.getDeclaringClass())) {
      try {
        return method.invoke(this, args);
      } catch (Throwable t) {
        throw ExceptionUtil.unwrapThrowable(t);
      }
    }
    final MapperMethod mapperMethod = cachedMapperMethod(method);
    return mapperMethod.execute(sqlSession, args);
  }
}
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1）String resource = "org/mybatis/example/mybatis-config.xml";
2）InputStream inputStream = Resources.getResourceAsStream(resource);
3）SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
4）SqlSession session = sqlSessionFactory.openSession();
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 UserDO user = (UserDO) sqlSession.select("com.alibaba.test.UserDao.getUser", userBO);
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public void select(String statement, Object parameter, RowBounds rowBounds, ResultHandler handler) {
  try {
    MappedStatement ms = configuration.getMappedStatement(statement);
    executor.query(ms, wrapCollection(parameter), rowBounds, handler);
  } catch (Exception e) {
    throw ExceptionFactory.wrapException("Error querying database.  Cause: " + e, e);
  } finally {
    ErrorContext.instance().reset();
  }
}
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 @Override
 public <E> List<E> query(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler) throws SQLException {
   // 1.根據具體傳入的引數，動態地生成需要執行的SQL語句，用BoundSql物件表示    
   BoundSql boundSql = ms.getBoundSql(parameter);
    // 2.為當前的查詢建立一個快取Key  
   CacheKey key = createCacheKey(ms, parameter, rowBounds, boundSql);
   return query(ms, parameter, rowBounds, resultHandler, key, boundSql);
}
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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()) {
    clearLocalCache();
  }
  List<E> list;
  try {
    queryStack++;
    list = resultHandler == null ? (List<E>) localCache.getObject(key) : null;
    if (list != null) {
      handleLocallyCachedOutputParameters(ms, key, parameter, boundSql);
    } else {
      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;
}
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private <E> List<E> queryFromDatabase(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql) throws SQLException {
  List<E> list;
  localCache.putObject(key, EXECUTION_PLACEHOLDER);
  try {
      //4. 執行查詢，返回List 結果，然後    將查詢的結果放入快取之中  
    list = doQuery(ms, parameter, rowBounds, resultHandler, boundSql);
  } finally {
    localCache.removeObject(key);
  }
  localCache.putObject(key, list);
  if (ms.getStatementType() == StatementType.CALLABLE) {
    localOutputParameterCache.putObject(key, parameter);
  }
  return list;
}
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@Override
public <E> List<E> doQuery(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) throws SQLException {
  Statement stmt = null;
  try {
     // 根據既有的引數，建立StatementHandler物件來執行查詢操作  
    Configuration configuration = ms.getConfiguration();
    StatementHandler handler = configuration.newStatementHandler(wrapper, ms, parameter, rowBounds, resultHandler, boundSql);
     //建立java.Sql.Statement物件，傳遞給StatementHandler物件  
    stmt = prepareStatement(handler, ms.getStatementLog());
      //呼叫StatementHandler.query()方法，返回List結果集  
    return handler.<E>query(stmt, resultHandler);
  } finally {
    closeStatement(stmt);
  }
}
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public StatementHandler newStatementHandler(Executor executor, MappedStatement mappedStatement, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) {
  StatementHandler statementHandler = new RoutingStatementHandler(executor, mappedStatement, parameterObject, rowBounds, resultHandler, boundSql);
  statementHandler = (StatementHandler) interceptorChain.pluginAll(statementHandler);
  return statementHandler;
}
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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;
}
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@Override
public <E> List<E> query(Statement statement, ResultHandler resultHandler) throws SQLException {
  PreparedStatement ps = (PreparedStatement) statement;
  ps.execute();
 return resultSetHandler.<E> handleResultSets(ps);
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@Override
public List<Object> handleResultSets(Statement stmt) throws SQLException {
  ErrorContext.instance().activity("handling results").object(mappedStatement.getId());

  final List<Object> multipleResults = new ArrayList<Object>();

  int resultSetCount = 0;
  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++;
    }
  }

  return collapseSingleResultList(multipleResults);
}
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