java-Mybatis源碼進階（二）(未完待續)

本文調試AutoContructorTest： fullyPopulatedSubject來閱讀mybatis源碼
第一篇博文已經獲取到Session連接了，這是第二篇博文獲取mapper

  @Test
  public void fullyPopulatedSubject() {
  //獲取session連接
    final SqlSession sqlSession = sqlSessionFactory.openSession();
    try {
    //下面重點解析getMapper(***)
      final AutoConstructorMapper mapper = sqlSession.getMapper(AutoConstructorMapper.class);
      final Object subject = mapper.getSubject(1);
      Assert.assertNotNull(subject);
    } finally {
      sqlSession.close();
    }
  }

1 sqlSession.getMapper(AutoConstructorMapper.class);
DefaultSqlSession.getMapper:

 @Override
  public <T> T getMapper(Class<T> type) {
    return configuration.<T>getMapper(type, this);
  }

mapperProxyFactory.newInstance:

public T newInstance(SqlSession sqlSession) {
    final MapperProxy<T> mapperProxy = new MapperProxy<T>(sqlSession, mapperInterface, methodCache);
    return newInstance(mapperProxy);
  }

然後，創建代理實例：
newInstance(mapperProxy)

 @SuppressWarnings("unchecked")
  protected T newInstance(MapperProxy<T> mapperProxy) {
    return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(), new Class[] { mapperInterface }, mapperProxy);
  }

1.2 final Object subject = mapper.getSubject(1);

2 AutoConstructMapper.java

package org.apache.ibatis.autoconstructor;

import org.apache.ibatis.annotations.Select;

import java.util.List;

public interface AutoConstructorMapper {
  @Select("SELECT * FROM subject WHERE id = #{id}")
  PrimitiveSubject getSubject(final int id);

  @Select("SELECT * FROM subject")
  List<PrimitiveSubject> getSubjects();

  @Select("SELECT * FROM subject")
  List<WrapperSubject> getWrapperSubjects();

  @Select("SELECT * FROM subject")
  List<AnnotatedSubject> getAnnotatedSubjects();

  @Select("SELECT * FROM subject")
  List<BadSubject> getBadSubjects();
}

2.1 介紹下mapper代理類MapperProxy.java：

package org.apache.ibatis.binding;

import java.io.Serializable;
import java.lang.invoke.MethodHandles;
import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.util.Map;

import org.apache.ibatis.lang.UsesJava7;
import org.apache.ibatis.reflection.ExceptionUtil;
import org.apache.ibatis.session.SqlSession;

/**
 * @author Clinton Begin
 * @author Eduardo Macarron
 */
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 {
      ////如果是Object中定義的方法，直接執行。如toString(),hashCode()等
      if (Object.class.equals(method.getDeclaringClass())) {
        return method.invoke(this, args);
      } else if (isDefaultMethod(method)) {
        //如果是默認的method則調用默認的method
        return invokeDefaultMethod(proxy, method, args);
      }
    } catch (Throwable t) {
      throw ExceptionUtil.unwrapThrowable(t);
    }

    final MapperMethod mapperMethod = cachedMapperMethod(method);
    //其他Mapper接口定義的方法交由mapperMethod來執行
    return mapperMethod.execute(sqlSession, args);
  }

  private MapperMethod cachedMapperMethod(Method method) {
    // private final Map<Method, MapperMethod> methodCache;
    //Mapper接口中的每個方法都會生成一個MapperMethod對象, methodCache維護着他們的對應關係
    // 獲取方法對象來獲取接口方法mapperMethod
    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();
  }
}

2.2 配置MapperMethod.command =new sqlCommand(…)
以及配置MapperMethod.method=new MethodSignature(…)

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

SqlCommand:

public SqlCommand(Configuration configuration, Class<?> mapperInterface, Method method) {
      final String methodName = method.getName();
      final Class<?> declaringClass = method.getDeclaringClass();
      MappedStatement ms = resolveMappedStatement(mapperInterface, methodName, declaringClass,
          configuration);
      if (ms == null) {
        if(method.getAnnotation(Flush.class) != null){
          name = null;
          type = SqlCommandType.FLUSH;
        } else {
          throw new BindingException("Invalid bound statement (not found): "
              + mapperInterface.getName() + "." + methodName);
        }
      } else {
        name = ms.getId();
        type = ms.getSqlCommandType();
        if (type == SqlCommandType.UNKNOWN) {
          throw new BindingException("Unknown execution method for: " + name);
        }
      }
    }

MethodSignature:

    public MethodSignature(Configuration configuration, Class<?> mapperInterface, Method method) {
      //解析具體某個接口的某個方法返回類型映射
      Type resolvedReturnType = TypeParameterResolver.resolveReturnType(method, mapperInterface);
      if (resolvedReturnType instanceof Class<?>) {
        //返回的是一個類
        this.returnType = (Class<?>) resolvedReturnType;
      } else if (resolvedReturnType instanceof ParameterizedType) {
        //返回的是一個參數類型
        this.returnType = (Class<?>) ((ParameterizedType) resolvedReturnType).getRawType();
      } else {
        //都不是，獲取返回類型並設置
        this.returnType = method.getReturnType();
      }
      //是否返回空
      this.returnsVoid = void.class.equals(this.returnType);
      //是否返回數組或列表
      this.returnsMany = configuration.getObjectFactory().isCollection(this.returnType) || this.returnType.isArray();
      //
      this.returnsCursor = Cursor.class.equals(this.returnType);
      this.returnsOptional = Jdk.optionalExists && Optional.class.equals(this.returnType);
      //是否返回的是一個map
      this.mapKey = getMapKey(method);
      //設置resultMap
      this.returnsMap = this.mapKey != null;

      this.rowBoundsIndex = getUniqueParamIndex(method, RowBounds.class);
      this.resultHandlerIndex = getUniqueParamIndex(method, ResultHandler.class);
      this.paramNameResolver = new ParamNameResolver(configuration, method);
    }

2.3 解析mappedstatement對象：
MapperMethod.resolveMappedStatement

private MappedStatement resolveMappedStatement(Class<?> mapperInterface, String methodName,
        Class<?> declaringClass, Configuration configuration) {
      //sql statement=接口名.方法名
      String statementId = mapperInterface.getName() + "." + methodName;
      if (configuration.hasStatement(statementId)) {
        //當前聲明映射是否存在，存在則返回已存在的mappedstatement
        return configuration.getMappedStatement(statementId);
      } else if (mapperInterface.equals(declaringClass)) {
        //聲明映射不存在，返回空
        return null;
      }
      //遞歸解析父接口的mappedstatement
      for (Class<?> superInterface : mapperInterface.getInterfaces()) {
        if (declaringClass.isAssignableFrom(superInterface)) {
          MappedStatement ms = resolveMappedStatement(superInterface, methodName,
              declaringClass, configuration);
          if (ms != null) {
            return ms;
          }
        }
      }
      return null;
    }

2.3 重點解析mapperMethod.execute(sqlSession, args)

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:
        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);
          if (method.returnsOptional() &&
              (result == null || !method.getReturnType().equals(result.getClass()))) {
            result = OptionalUtil.ofNullable(result);
          }
        }
        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 <E> List<E> query(MappedStatement ms, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler) throws SQLException {
    BoundSql boundSql = ms.getBoundSql(parameterObject);
    CacheKey key = createCacheKey(ms, parameterObject, rowBounds, boundSql);
    return query(ms, parameterObject, rowBounds, resultHandler, key, boundSql);
  }