一次在做一個專案的過程中，發現mybatis載入xml檔案錯誤，導致了後面所有的sql都報了這個sql語句的錯誤，一時沒有摸到頭腦，在此分析下。

在mybatis載入xml檔案的時候，會解析所有的檔案，同時把statement錯誤的檔案放到一個集合中去，程式碼如下：

  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);
 

      }
    }
  }

  public void addIncompleteStatement(XMLStatementBuilder incompleteStatement) {
    incompleteStatements.add(incompleteStatement);
  }

incompleteStatements是載入錯誤的Statements集合。而當每次執行任何sql語句的時候，都會檢查incompleteStatements是否為空，如果為空的話，就一直報那個載入錯誤的xml檔案。程式碼如下：

我們從MapperProxy類的invoke方法一直往下走：

  public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
    if (method.getDeclaringClass() == Object.class) {
      return method.invoke(this, args);
    }
    final Class<?> declaringInterface = findDeclaringInterface(proxy, method);
    final MapperMethod mapperMethod = new MapperMethod(declaringInterface, method, sqlSession);
 

    final Object result = mapperMethod.execute(args);
    if (result == null && method.getReturnType().isPrimitive() && !method.getReturnType().equals(Void.TYPE)) {
      throw new BindingException("Mapper method '" + method.getName() + "' (" + method.getDeclaringClass() + ") attempted to return null from a method with a primitive return type (" + method.getReturnType() + ").");
    }
    return result;
  }

  public MapperMethod(Class<?> declaringInterface, Method method, SqlSession sqlSession) {
    paramNames = new ArrayList<String>();
    paramPositions = new ArrayList<Integer>();
    this.sqlSession = sqlSession;
    this.method = method;
    this.config = sqlSession.getConfiguration();
    this.hasNamedParameters = false;
    this.declaringInterface = declaringInterface;
    this.objectFactory = config.getObjectFactory();
    setupFields();//設定欄位
    setupMethodSignature();//設定方法驗證
    setupCommandType();//命令型別：select，update，delete，insert
    validateStatement();//驗證statement
  }

  private void setupCommandType() {
    MappedStatement ms = config.getMappedStatement(commandName);
    type = ms.getSqlCommandType();
    if (type == SqlCommandType.UNKNOWN) {
      throw new BindingException("Unknown execution method for: " + commandName);
    }
  }

  public MappedStatement getMappedStatement(String id, boolean validateIncompleteStatements) {
    if (validateIncompleteStatements) {
      buildAllStatements();
    }
    return mappedStatements.get(id);
  }

  protected void buildAllStatements() {
    if (!incompleteResultMaps.isEmpty()) {
      synchronized (incompleteResultMaps) {
        // This always throws a BuilderException.
        incompleteResultMaps.iterator().next().resolve();
      }
    }
    if (!incompleteCacheRefs.isEmpty()) {
      synchronized (incompleteCacheRefs) {
        // This always throws a BuilderException.
        incompleteCacheRefs.iterator().next().resolveCacheRef();
      }
    }
    if (!incompleteStatements.isEmpty()) {
      synchronized (incompleteStatements) {
        // This always throws a BuilderException.
        incompleteStatements.iterator().next().parseStatementNode();
      }
    }
  }