Mybatis执行SQL命令的流程分析

目录

• MapperProxy的功能：
• MapperMethod的功能：

MyBATis中的Sql命令，在枚举类SqlCommandType中定义的。

public enum SqlCommandType {  
    UNKNOWN, INSERT, UPDATE, DELETE, SELECT, FLUSH;
}

下面，我们以Mapper接口中的一个方法作为例子，看看Sql命令的执行完整流程。

public interface StudentMapper {
  List<Student> findAllStudents(Map<String, Object> map, RowBounds rowBounds, ResultSetHandler rh);  
}

参数RowBounds和ResultSetHandler是可选参数，表示分页对象和自定义结果集处理器，一般不需要。

一个完整的Sql命令，其执行的完整流程图如下：

对于上面的流程图，如果看过前面的文章的话，大部分对象我们都比较熟悉了。一个图，就完整展示了其执行流程。

MapperProxy的功能：

1. 因为Mapper接口不能直接实例化，MapperProxy的作用，就是使用JDK动态代理功能，间接实例化Mapper的proxy对象。可参看系列的第二篇。

2. 缓存MapperMethod对象。

private final Map<Method, MapperMethod> methodCache;
@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);
    }
  }
  // 投鞭断流
  final MapperMethod mapperMethod = cachedMapperMethod(method);
  return mapperMethod.execute(sqlSession, args);
}
 
// 缓存MapperMethod
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;
}

MapperMethod的功能：

1. 解析Mapper接口的方法，并封装成MapperMethod对象。

2. 将Sql命令，正确路由到恰当的SqlSession的方法上。

public class MapperMethod {
 
    // 保存了Sql命令的类型和键id
    private final SqlCommand command;
    // 保存了Mapper接口方法的解析信息
    private final MethodSignature method;
  
    public MapperMethod(Class<?> mapperInterface, Method method, Configuration config) {
      this.command = new SqlCommand(config, mapperInterface, method);
      this.method = new MethodSignature(config, method);
    }
  
    // 根据解析结果，路由到恰当的SqlSession方法上
    public Object execute(SqlSession sqlSession, Object[] args) {
      Object result;
      if (SqlCommandType.INSERT == command.getType()) {
        Object param = method.convertArgsToSqlCommandParam(args);
        result = rowCountResult(sqlSession.insert(command.getName(), param));
      } else if (SqlCommandType.UPDATE == command.getType()) {
        Object param = method.convertArgsToSqlCommandParam(args);
        result = rowCountResult(sqlSession.update(command.getName(), param));
      } else if (SqlCommandType.DELETE == command.getType()) {
        Object param = method.convertArgsToSqlCommandParam(args);
        result = rowCountResult(sqlSession.delete(command.getName(), param));
      } else if (SqlCommandType.SELECT == command.getType()) {
        if (method.returnsVoid() && method.hasResultHandler()) {
          executeWithResultHandler(sqlSession, args);
          result = null;
        } else if (method.returnsMany()) {
          result = exe编程客栈cuteForMany(sqlSession, args);
        } else if (method.returnsMap()) {
          result = executeForMap(sqlSession, args);
        } else {
          Object param = method.convertArgsToSqlCommandParam(args);
          result = sqlSession.selectOne(command.getName(), param);
        }
      } else if (SqlCommandType.FLUSH == command.getType()) {
          result = sqlSession.flushStatements();
      } else {
        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;
    }

org.apache.ibatis.binding.MapperMethod.SqlCommand。

public static class SqlCommand {
    // full id, 通过它可以找到MappedStatement
    private final String name;
    private final SqlCommandType type;

org.apache.ibatis.binding.MapperMethod.MethodSignature：

public static class MethodSignature {
    private f开发者_JAV培训inal boolean returnsMany;
    private final boolean returnsMap;
    private final boolean returnsVoid;
    private final Class<?> returnType;
    private final String mapKey;
    private final Integer resultHandlerIndex;
    private final Integer rowBoundsIndex;
    private final SortedMap<Integer, String> params;
    private final boolean hasNamedParameters;
 
    public MENzurbBeethodSignature(Configuration configuration, Method method) {
      this.returnType = method.getReturnType();
      this.returnjssVoid = void.class.equals(this.returnType);
      this.returnsMany = (configuration.getObjectFactory().isCollection(this.returnType) || this.returnType.isArray());
      this.mapKey = getMapKey(method);
      this.returnsMap = (this.mapKey != null);
      thipythons.hasNamedParameters = hasNamedParams(method);
      // 分页参数
      this.rowBoundsIndex = getUniqueParamIndex(method, RowBounds.class);
      // 自定义ResultHandler
      this.resultHandlerIndex = getUniqueParamIndex(method, ResultHandler.class);
      this.params = Collections.unmodifiableSortedMap(getParams(method, this.hasNamedParameters));
    }

以上是对MapperMethod的补充说明。 

到此这篇关于Mybatis执行SQL命令的完整流程的文章就介绍到这了,更多相关Mybatis执行SQL命令内容请搜索我们以前的文章或继续浏览下面的相关文章希望大家以后多多支持我们！