mybatis接口式编程 调用接口得到数据

首先需要知道代理设计模式。
mapper只是个接口，并没有能力实现方法。
当调用mapper接口，最终的调用的方法是由MapperProxy代理实现类中invoke方法实现的。

public class MapperProxy<T> implements InvocationHandler, Serializable { private static final long serialVersionUID = -6424540398559729838L; private final SqlSession sqlSession; private final Class<T> mapperInterface; private final Map<Method, MapperMethod> methodCache; public MapperProxy(SqlSession sqlSession, Class<T> mapperInterface, Map<Method, MapperMethod> methodCache) { this.sqlSession = sqlSession; this.mapperInterface = mapperInterface; this.methodCache = methodCache; } @Override public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { //如果调用的方法的所在类是Object if (Object.class.equals(method.getDeclaringClass())) { try { return method.invoke(this, args); } catch (Throwable t) { throw ExceptionUtil.unwrapThrowable(t); } } //相当于一个map，key：拦截方法对应对的sql，value：相当于组装的一段jdbc的代码 final MapperMethod mapperMethod = cachedMapperMethod(method); // return mapperMethod.execute(sqlSession, args); } private MapperMethod cachedMapperMethod(Method method) { //先从缓存map中取 MapperMethod mapperMethod = methodCache.get(method); if (mapperMethod == null) { //SqlCommand command; //MethodSignature method; mapperMethod = new MapperMethod(mapperInterface, method, sqlSession.getConfiguration()); methodCache.put(method, mapperMethod); } return mapperMethod; } } 

其中很明显的可以看到需要先生成MapperMethod，MapperMethod有两个字段分别是SqlCommand command; final MethodSignature method

• SqlCommand command
  其中又有两个字段String name（mapper中namespace+Sql的id）; SqlCommandType type（Sql语句的类型，UNKNOWN, INSERT, UPDATE, DELETE, SELECT, FLUSH;）
• MethodSignature method
  存放于这条sql语句组装的所对应的jdbc代码。
  接下来看看execute方法。先判断是什么类型的sql语句

public Object execute(SqlSession sqlSession, Object[] args) { Object result; switch (command.getType()) { case INSERT: { 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: //返回的是否是void，方法中是否含有结果映射 if (method.returnsVoid() && method.hasResultHandler()) { executeWithResultHandler(sqlSession, args); result = null; //是否返回多个值 } 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 { //返回简单数据 //做一个转换，将Java中的参数转换成符合sql的参数类型 Object param = method.convertArgsToSqlCommandParam(args); //调用sqlsession执行。其他的几个也是通过一些设置，最终还是通过调用sqlSession中的方法来执行 result = sqlSession.selectOne(command.getName(), param); } break; case FLUSH: result = sqlSession.flushStatements(); break; default: 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; } 

@Override public <T> T selectOne(String statement, Object parameter) { // Popular vote was to return null on 0 results and throw exception on too many. List<T> list = this.<T>selectList(statement, parameter); if (list.size() == 1) { return list.get(0); } else if (list.size() > 1) { throw new TooManyResultsException("Expected one result (or null) to be returned by selectOne(), but found: " + list.size()); } else { return null; } } 

selectOne方法其实是通过selectList查询最终取得第一条数据。

@Override public <E> List<E> selectList(String statement, Object parameter, RowBounds rowBounds) { try { //statement就是command.getName()，mapper.xml中namespace+Sql的id获取MappedStatement  //MappedStatement是与之对应的JDBC的代码组成，属性成员比较多 MappedStatement ms = configuration.getMappedStatement(statement); //最终调用四大神器的执行器 执行代码 return executor.query(ms, wrapCollection(parameter), rowBounds, Executor.NO_RESULT_HANDLER); } catch (Exception e) { throw ExceptionFactory.wrapException("Error querying database.  Cause: " + e, e); } finally { ErrorContext.instance().reset(); } } 

最后代码运行到执行器，开始到Jdbc的调用流程。接下来看看执行器的相关流程
执行器

本文地址：https://blog.csdn.net/wsdfym/article/details/107895864