mybatis的statement的解析与加载

问题

mybatis的xml中的sql语句是启动时生成JDK代理类的时候就生成一次么

调用顺序链

• 解析xml配置

  Reader reader = Resources.getResourceAsReader("mybatis-config.xml");        sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);

• 调用SqlSessionFactoryBuilder的方法

  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.      }    }  }

• 调用XMLConfigBuilder.parser

  public Configuration parse() {    if (parsed) {      throw new BuilderException("Each XMLConfigBuilder can only be used once.");    }    parsed = true;    parseConfiguration(parser.evalNode("/configuration"));    return configuration;  }

• sqlSessionFactory.getConfiguration().addMapper(BookMapper.class);触发MapperRegistry.addMapper

  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<T>(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);        }      }    }  }

• 触发MapperAnnotationBuilder.parse方法

  public void parse() {    String resource = type.toString();    if (!configuration.isResourceLoaded(resource)) {      loadXmlResource();      configuration.addLoadedResource(resource);      assistant.setCurrentNamespace(type.getName());      parseCache();      parseCacheRef();      Method[] methods = type.getMethods();      for (Method method : methods) {        try {          // issue #237          if (!method.isBridge()) {            parseStatement(method);          }        } catch (IncompleteElementException e) {          configuration.addIncompleteMethod(new MethodResolver(this, method));        }      }    }    parsePendingMethods();  }

• 触发触发MapperAnnotationBuilder.loadXmlResource

  private void loadXmlResource() {    // Spring may not know the real resource name so we check a flag    // to prevent loading again a resource twice    // this flag is set at XMLMapperBuilder#bindMapperForNamespace    if (!configuration.isResourceLoaded("namespace:" + type.getName())) {      String xmlResource = type.getName().replace('.', '/') + ".xml";      InputStream inputStream = null;      try {        inputStream = Resources.getResourceAsStream(type.getClassLoader(), xmlResource);      } catch (IOException e) {        // ignore, resource is not required      }      if (inputStream != null) {        XMLMapperBuilder xmlParser = new XMLMapperBuilder(inputStream, assistant.getConfiguration(), xmlResource, configuration.getSqlFragments(), type.getName());        xmlParser.parse();      }    }  }

  • 触发XMLMapperBuilder.parse

      public void parse() {    if (!configuration.isResourceLoaded(resource)) {      configurationElement(parser.evalNode("/mapper"));      configuration.addLoadedResource(resource);      bindMapperForNamespace();    }    parsePendingResultMaps();    parsePendingChacheRefs();    parsePendingStatements();  }

• 触发XMLMapperBuilder.configurationElement

  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);      cacheRefElement(context.evalNode("cache-ref"));      cacheElement(context.evalNode("cache"));      parameterMapElement(context.evalNodes("/mapper/parameterMap"));      resultMapElements(context.evalNodes("/mapper/resultMap"));      sqlElement(context.evalNodes("/mapper/sql"));      buildStatementFromContext(context.evalNodes("select|insert|update|delete"));    } catch (Exception e) {      throw new BuilderException("Error parsing Mapper XML. Cause: " + e, e);    }  }

• 触发XMLMapperBuilder.buildStatementFromContext

  private void buildStatementFromContext(List<XNode> list, String requiredDatabaseId) {    for (XNode context : list) {      final XMLStatementBuilder statementParser = new XMLStatementBuilder(configuration, builderAssistant, context, requiredDatabaseId);      try {        statementParser.parseStatementNode();      } catch (IncompleteElementException e) {        configuration.addIncompleteStatement(statementParser);      }    }  }

• 触发XMLStatementBuilder.parseStatementNode

  public void parseStatementNode() {    String id = context.getStringAttribute("id");    String databaseId = context.getStringAttribute("databaseId");    if (!databaseIdMatchesCurrent(id, databaseId, this.requiredDatabaseId)) {      return;    }    Integer fetchSize = context.getIntAttribute("fetchSize");    Integer timeout = context.getIntAttribute("timeout");    String parameterMap = context.getStringAttribute("parameterMap");    String parameterType = context.getStringAttribute("parameterType");    Class<?> parameterTypeClass = resolveClass(parameterType);    String resultMap = context.getStringAttribute("resultMap");    String resultType = context.getStringAttribute("resultType");    String lang = context.getStringAttribute("lang");    LanguageDriver langDriver = getLanguageDriver(lang);    Class<?> resultTypeClass = resolveClass(resultType);    String resultSetType = context.getStringAttribute("resultSetType");    StatementType statementType = StatementType.valueOf(context.getStringAttribute("statementType", StatementType.PREPARED.toString()));    ResultSetType resultSetTypeEnum = resolveResultSetType(resultSetType);    String nodeName = context.getNode().getNodeName();    SqlCommandType sqlCommandType = SqlCommandType.valueOf(nodeName.toUpperCase(Locale.ENGLISH));    boolean isSelect = sqlCommandType == SqlCommandType.SELECT;    boolean flushCache = context.getBooleanAttribute("flushCache", !isSelect);    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());    // Parse selectKey after includes and remove them.    processSelectKeyNodes(id, parameterTypeClass, langDriver);    // Parse the SQL (pre: <selectKey> and <include> were parsed and removed)    SqlSource sqlSource = langDriver.createSqlSource(configuration, context, parameterTypeClass);    String resultSets = context.getStringAttribute("resultSets");    String keyProperty = context.getStringAttribute("keyProperty");    String keyColumn = context.getStringAttribute("keyColumn");    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))          ? new Jdbc3KeyGenerator() : new NoKeyGenerator();    }    builderAssistant.addMappedStatement(id, sqlSource, statementType, sqlCommandType,        fetchSize, timeout, parameterMap, parameterTypeClass, resultMap, resultTypeClass,        resultSetTypeEnum, flushCache, useCache, resultOrdered,         keyGenerator, keyProperty, keyColumn, databaseId, langDriver, resultSets);  }

• 触发MapperBuilderAssistant.addMappedStatement将解析好的statement放到configuration的map中

  public void addMappedStatement(MappedStatement ms) {    mappedStatements.put(ms.getId(), ms);  }

sql的组装

• MappedStatement.getBoundSql

  public BoundSql getBoundSql(Object parameterObject) {    BoundSql boundSql = sqlSource.getBoundSql(parameterObject);    List<ParameterMapping> parameterMappings = boundSql.getParameterMappings();    if (parameterMappings == null || parameterMappings.isEmpty()) {      boundSql = new BoundSql(configuration, boundSql.getSql(), parameterMap.getParameterMappings(), parameterObject);    }    // check for nested result maps in parameter mappings (issue #30)    for (ParameterMapping pm : boundSql.getParameterMappings()) {      String rmId = pm.getResultMapId();      if (rmId != null) {        ResultMap rm = configuration.getResultMap(rmId);        if (rm != null) {          hasNestedResultMaps |= rm.hasNestedResultMaps();        }      }    }    return boundSql;  }

  里头主要是把sql语句和参数组成BoundSql对象

• 调用BaseExecutor的query方法

  @Override  public <E> List<E> query(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler) throws SQLException {    BoundSql boundSql = ms.getBoundSql(parameter);    CacheKey key = createCacheKey(ms, parameter, rowBounds, boundSql);    return query(ms, parameter, rowBounds, resultHandler, key, boundSql); }

• getBoundSql调用RawSqlSource调用StaticSqlSource的getBoundSql

  public BoundSql getBoundSql(Object parameterObject) {    return new BoundSql(configuration, sql, parameterMappings, parameterObject);  }

  这里的sql就是mapper里头写得select * from book where id = ? limit 1

• BaseExecutor.queryFromDatabase

  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 {      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;  }

• 调用SimpleExecutor.doQuery生成JDBC的statement

  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.<E>query(stmt, resultHandler);    } finally {      closeStatement(stmt);    }  }

• 调用StatementHandler来具体处理,这里是RoutingStatementHandler委托PreparedStatementHandler来处理sql的生成

  public Statement prepare(Connection connection) throws SQLException {    return delegate.prepare(connection);  }

• 回调BaseStatementHandler的prepare方法

  public Statement prepare(Connection connection) throws SQLException {    ErrorContext.instance().sql(boundSql.getSql());    Statement statement = null;    try {      statement = instantiateStatement(connection);      setStatementTimeout(statement);      setFetchSize(statement);      return statement;    } catch (SQLException e) {      closeStatement(statement);      throw e;    } catch (Exception e) {      closeStatement(statement);      throw new ExecutorException("Error preparing statement.  Cause: " + e, e);    }  }

• 在调用PreparedStatementHandler的instantiateStatement

  protected Statement instantiateStatement(Connection connection) throws SQLException {    String sql = boundSql.getSql();    if (mappedStatement.getKeyGenerator() instanceof Jdbc3KeyGenerator) {      String[] keyColumnNames = mappedStatement.getKeyColumns();      if (keyColumnNames == null) {        return connection.prepareStatement(sql, PreparedStatement.RETURN_GENERATED_KEYS);      } else {        return connection.prepareStatement(sql, keyColumnNames);      }    } else if (mappedStatement.getResultSetType() != null) {      return connection.prepareStatement(sql, mappedStatement.getResultSetType().getValue(), ResultSet.CONCUR_READ_ONLY);    } else {      return connection.prepareStatement(sql);    }  }

• 组装statement之后，填充参数

  public void parameterize(Statement statement) throws SQLException {    parameterHandler.setParameters((PreparedStatement) statement);  }

• 调用DefaultParameterHandler.setParameters方法，自此完成sql的拼装

  public void setParameters(PreparedStatement ps) {    ErrorContext.instance().activity("setting parameters").object(mappedStatement.getParameterMap().getId());    List<ParameterMapping> parameterMappings = boundSql.getParameterMappings();    if (parameterMappings != null) {      for (int i = 0; i < parameterMappings.size(); i++) {        ParameterMapping parameterMapping = parameterMappings.get(i);        if (parameterMapping.getMode() != ParameterMode.OUT) {          Object value;          String propertyName = parameterMapping.getProperty();          if (boundSql.hasAdditionalParameter(propertyName)) { // issue #448 ask first for additional params            value = boundSql.getAdditionalParameter(propertyName);          } else if (parameterObject == null) {            value = null;          } else if (typeHandlerRegistry.hasTypeHandler(parameterObject.getClass())) {            value = parameterObject;          } else {            MetaObject metaObject = configuration.newMetaObject(parameterObject);            value = metaObject.getValue(propertyName);          }          TypeHandler typeHandler = parameterMapping.getTypeHandler();          JdbcType jdbcType = parameterMapping.getJdbcType();          if (value == null && jdbcType == null) {            jdbcType = configuration.getJdbcTypeForNull();          }          try {            typeHandler.setParameter(ps, i + 1, value, jdbcType);          } catch (TypeException e) {            throw new TypeException("Could not set parameters for mapping: " + parameterMapping + ". Cause: " + e, e);          } catch (SQLException e) {            throw new TypeException("Could not set parameters for mapping: " + parameterMapping + ". Cause: " + e, e);          }        }      }    }  }