public class UserDaoTest {

  private SqlSessionFactory sqlSessionFactory;

  @Before
  public void setUp() throws Exception{
    ClassPathResource resource = new ClassPathResource("mybatis-config.xml");
    InputStream inputStream = resource.getInputStream();
    sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
  }

  @Test
  public void selectUserTest(){
    String id = "{0003CCCA-AEA9-4A1E-A3CC-06D884BA3906}";
    SqlSession sqlSession = sqlSessionFactory.openSession();
    CbondissuerMapper cbondissuerMapper = sqlSession.getMapper(CbondissuerMapper.class);
    Cbondissuer cbondissuer = cbondissuerMapper.selectByPrimaryKey(id);
    System.out.println(cbondissuer);
    sqlSession.close();
  }

}

public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
  //mapperRegistry實(shí)質(zhì)上是一個(gè)Map，里面注冊(cè)了啟動(dòng)過程中解析的各種Mapper.xml
  //mapperRegistry的key是接口的全限定名，比如com.csx.demo.spring.boot.dao.SysUserMapper
  //mapperRegistry的Value是MapperProxyFactory,用于生成對(duì)應(yīng)的MapperProxy（動(dòng)態(tài)代理類）
  return mapperRegistry.getMapper(type, sqlSession);
}

public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
  final MapperProxyFactory<T> mapperProxyFactory = (MapperProxyFactory<T>) knownMappers.get(type);
  //如果配置文件中沒有配置相關(guān)Mapper,直接拋異常
  if (mapperProxyFactory == null) {
   throw new BindingException("Type " + type + " is not known to the MapperRegistry.");
  }
  try {
   //關(guān)鍵方法
   return mapperProxyFactory.newInstance(sqlSession);
  } catch (Exception e) {
   throw new BindingException("Error getting mapper instance. Cause: " + e, e);
  }
 }

public class MapperProxyFactory<T> {

 private final Class<T> mapperInterface;
 private final Map<Method, MapperMethod> methodCache = new ConcurrentHashMap<Method, MapperMethod>();

 public MapperProxyFactory(Class<T> mapperInterface) {
  this.mapperInterface = mapperInterface;
 }

 public Class<T> getMapperInterface() {
  return mapperInterface;
 }

 public Map<Method, MapperMethod> getMethodCache() {
  return methodCache;
 }

 //生成Mapper接口的動(dòng)態(tài)代理類MapperProxy
 @SuppressWarnings("unchecked")
 protected T newInstance(MapperProxy<T> mapperProxy) {
  return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(), new Class[] { mapperInterface }, mapperProxy);
 }
 
 public T newInstance(SqlSession sqlSession) {
  final MapperProxy<T> mapperProxy = new MapperProxy<T>(sqlSession, mapperInterface, methodCache);
  return newInstance(mapperProxy);
 }

}

//MapperProxy代理類
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 {
  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);
  }
  //獲取MapperMethod，并調(diào)用MapperMethod
  final MapperMethod mapperMethod = cachedMapperMethod(method);
  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;
 }

 @UsesJava7
 private Object invokeDefaultMethod(Object proxy, Method method, Object[] args)
   throws Throwable {
  final Constructor<MethodHandles.Lookup> constructor = MethodHandles.Lookup.class
    .getDeclaredConstructor(Class.class, int.class);
  if (!constructor.isAccessible()) {
   constructor.setAccessible(true);
  }
  final Class<?> declaringClass = method.getDeclaringClass();
  return constructor
    .newInstance(declaringClass,
      MethodHandles.Lookup.PRIVATE | MethodHandles.Lookup.PROTECTED
        | MethodHandles.Lookup.PACKAGE | MethodHandles.Lookup.PUBLIC)
    .unreflectSpecial(method, declaringClass).bindTo(proxy).invokeWithArguments(args);
 }

 /**
  * Backport of java.lang.reflect.Method#isDefault()
  */
 private boolean isDefaultMethod(Method method) {
  return ((method.getModifiers()
    & (Modifier.ABSTRACT | Modifier.PUBLIC | Modifier.STATIC)) == Modifier.PUBLIC)
    && method.getDeclaringClass().isInterface();
 }
}

public Object execute(SqlSession sqlSession, Object[] args) {
  Object result;
  //判斷是CRUD那種方法
  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:
    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());
  }
  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;
 }

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();
   //內(nèi)部封裝了ParameterHandler和ResultSetHandler
   StatementHandler handler = configuration.newStatementHandler(wrapper, ms, parameter, rowBounds, resultHandler, boundSql);
   stmt = prepareStatement(handler, ms.getStatementLog());
   //StatementHandler封裝了Statement, 讓 StatementHandler 去處理
   return handler.<E>query(stmt, resultHandler);
  } finally {
   closeStatement(stmt);
  }
 }

public <E> List<E> query(Statement statement, ResultHandler resultHandler) throws SQLException {
   //到此，原形畢露， PreparedStatement, 這個(gè)大家都已經(jīng)滾瓜爛熟了吧
  PreparedStatement ps = (PreparedStatement) statement;
  ps.execute();
  //結(jié)果交給了ResultSetHandler 去處理,處理完之后返回給客戶端
  return resultSetHandler.<E> handleResultSets(ps);
 }