详述mybatis执行流程

系列

• MyBatis拦截器原理介绍
• Mybatis拦截器改写请求参数和结果
• Mybatis 插件兼容动态SQL
• mybatis 参数解析流程附相关案例
• 详述mybatis执行流程

开篇

• 写这篇文章纯粹是为了更好的理顺 mybatis 的执行流程。
• mybatis 的执行流程具体可参考下面的流程图，基于 mybatis 3.4.6版本进行的分析。

mybatis执行流程

• 核心流程一是指mapperMethod的执行流程，这个过程主要是指请求参数的解析。
• 核心流程二是指executor的执行流程，这个过程主要是指StatementHandler的创建，包含 BoundSql 的创建、parameterHandler和 ResultSetHandler 的创建。
• StatementHandler 执行流程，这部分主要执行 SQL 并对结果集进行处理。
• 核心点：参数的组装在 exector 之前前，同样在所有的拦截器执行前，BoundSql的时机在于 statementHandler 的创建，早于parameterHandler和 ResultSetHandler 的时机。

MapperMethod

MapperMethod对象创建

public class MapperProxy implements InvocationHandler, Serializable {

  @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 (isDefaultMethod(method)) {
        return invokeDefaultMethod(proxy, method, args);
      }
    } catch (Throwable t) {
      throw ExceptionUtil.unwrapThrowable(t);
    }
    final MapperMethod mapperMethod = cachedMapperMethod(method);

    // 执行MapperMethod的 execute 方法
    return mapperMethod.execute(sqlSession, args);
  }

  private MapperMethod cachedMapperMethod(Method method) {
    MapperMethod mapperMethod = methodCache.get(method);
    if (mapperMethod == null) {
      mapperMethod = new MapperMethod(mapperInterface, method, sqlSession.getConfiguration());
      methodCache.put(method, mapperMethod);
    }
    return mapperMethod;
  }
}

• MapperProxy的核心在于创建MapperMethod对象。
• MapperMethod的对象的创建过程中涉及mybatis内部请求参数的封装。
• 通过执行mapperMethod的execute方法继续执行。
  
  

public class MapperMethod {

  private final SqlCommand command;
  private final MethodSignature method;

  public MapperMethod(Class mapperInterface, Method method, Configuration config) {
    this.command = new SqlCommand(config, mapperInterface, method);
    // 创建MethodSignature对象
    this.method = new MethodSignature(config, mapperInterface, method);
  }


  public static class MethodSignature {

    private final boolean returnsMany;
    private final boolean returnsMap;
    private final boolean returnsVoid;
    private final boolean returnsCursor;
    private final Class returnType;
    private final String mapKey;
    private final Integer resultHandlerIndex;
    private final Integer rowBoundsIndex;
    private final ParamNameResolver paramNameResolver;

    public MethodSignature(Configuration configuration, Class mapperInterface, Method method) {
      Type resolvedReturnType = TypeParameterResolver.resolveReturnType(method, mapperInterface);
      if (resolvedReturnType instanceof Class) {
        this.returnType = (Class) resolvedReturnType;
      } else if (resolvedReturnType instanceof ParameterizedType) {
        this.returnType = (Class) ((ParameterizedType) resolvedReturnType).getRawType();
      } else {
        this.returnType = method.getReturnType();
      }
      this.returnsVoid = void.class.equals(this.returnType);
      this.returnsMany = configuration.getObjectFactory().isCollection(this.returnType) || this.returnType.isArray();
      this.returnsCursor = Cursor.class.equals(this.returnType);
      this.mapKey = getMapKey(method);
      this.returnsMap = this.mapKey != null;
      this.rowBoundsIndex = getUniqueParamIndex(method, RowBounds.class);
      this.resultHandlerIndex = getUniqueParamIndex(method, ResultHandler.class);
      // 创建ParamNameResolver参数解析对象
      this.paramNameResolver = new ParamNameResolver(configuration, method);
    }

    public Object convertArgsToSqlCommandParam(Object[] args) {
      return paramNameResolver.getNamedParams(args);
    }
}

• MapperMethod的创建核心在于构建方法签名参数MethodSignature。
• MethodSignature的convertArgsToSqlCommandParam完成mybatis请求参数的封装。
  
  

MapperMethod执行流程

public class MapperMethod {

  private final SqlCommand command;
  private final MethodSignature method;

  public MapperMethod(Class mapperInterface, Method method, Configuration config) {
    this.command = new SqlCommand(config, mapperInterface, method);
    this.method = new MethodSignature(config, mapperInterface, method);
  }

  public Object execute(SqlSession sqlSession, Object[] args) {
    Object result;
    switch (command.getType()) {
      case INSERT: {
        // 调用MethodSignature的convertArgsToSqlCommandParam参数转换方法
        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()) {
          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);
        }
        break;
      case FLUSH:
        result = sqlSession.flushStatements();
        break;
      default:
        throw new BindingException("Unknown execution method for: " + command.getName());
    }
    return result;
  }

    public Object convertArgsToSqlCommandParam(Object[] args) {
      return paramNameResolver.getNamedParams(args);
    }
}

• MapperMethod#execute通过MapperMethod#convertArgsToSqlCommandParam完成参数请求参数的解析。
• 执行DefaultSqlSession的update/insert/select/delete等操作。
• 参数的解析convertArgsToSqlCommandParam在真正执行 Executor 方法之前

public class ParamNameResolver {

  private static final String GENERIC_NAME_PREFIX = "param";
  private final SortedMap names;
  private boolean hasParamAnnotation;

  public Object getNamedParams(Object[] args) {
    final int paramCount = names.size();
    if (args == null || paramCount == 0) {
      return null;
    } else if (!hasParamAnnotation && paramCount == 1) {
      return args[names.firstKey()];
    } else {
      final Map param = new ParamMap