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+# MapperMethod
+- 源码地址: `org.apache.ibatis.binding.MapperMethod`,核心方法是`execute`
+
+```java
+    /**
+     * CRUD 不同的执行处理
+     *
+     * @param sqlSession
+     * @param args
+     * @return
+     */
+    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 = Optional.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;
+    }
+
+```
+
+```java
+    /**
+     * 根据 resultHandler 进行处理
+     *
+     * @param sqlSession
+     * @param args
+     */
+    private void executeWithResultHandler(SqlSession sqlSession, Object[] args) {
+        MappedStatement ms = sqlSession.getConfiguration().getMappedStatement(command.getName());
+        if (!StatementType.CALLABLE.equals(ms.getStatementType())
+                && void.class.equals(ms.getResultMaps().get(0).getType())) {
+            throw new BindingException("method " + command.getName()
+                    + " needs either a @ResultMap annotation, a @ResultType annotation,"
+                    + " or a resultType attribute in XML so a ResultHandler can be used as a parameter.");
+        }
+        Object param = method.convertArgsToSqlCommandParam(args);
+        // 判断是否有 RowBounds
+        if (method.hasRowBounds()) {
+            RowBounds rowBounds = method.extractRowBounds(args);
+            sqlSession.select(command.getName(), param, rowBounds, method.extractResultHandler(args));
+        } else {
+            sqlSession.select(command.getName(), param, method.extractResultHandler(args));
+        }
+    }
+
+```
+
+
+- 返回值为多个的情况
+```java
+    /**
+     * 针对多个查询结果进行 ,转换成不同的 list 或者数组
+     *
+     * @param sqlSession
+     * @param args
+     * @param <E>
+     * @return
+     */
+    private <E> Object executeForMany(SqlSession sqlSession, Object[] args) {
+        List<E> result;
+        Object param = method.convertArgsToSqlCommandParam(args);
+        if (method.hasRowBounds()) {
+            RowBounds rowBounds = method.extractRowBounds(args);
+            // 直接 list
+            result = sqlSession.selectList(command.getName(), param, rowBounds);
+        } else {
+            result = sqlSession.selectList(command.getName(), param);
+        }
+        // issue #510 Collections & arrays support
+        if (!method.getReturnType().isAssignableFrom(result.getClass())) {
+            if (method.getReturnType().isArray()) {
+                // 转换成 array
+                return convertToArray(result);
+            } else {
+                // 转换成 collection
+                return convertToDeclaredCollection(sqlSession.getConfiguration(), result);
+            }
+        }
+        return result;
+    }
+
+```
+
+### convertToArray
+```java
+    /**
+     * 转换为数组
+     *
+     * @param list 数据库查询结果
+     * @param <E>
+     * @return
+     */
+    @SuppressWarnings("unchecked")
+    private <E> Object convertToArray(List<E> list) {
+        // 获取返回类型
+        Class<?> arrayComponentType = method.getReturnType().getComponentType();
+        // new 一个 array
+        Object array = Array.newInstance(arrayComponentType, list.size());
+        if (arrayComponentType.isPrimitive()) {
+            for (int i = 0; i < list.size(); i++) {
+                Array.set(array, i, list.get(i));
+            }
+            return array;
+        } else {
+            // 通过  toArray方法转换
+            return list.toArray((E[]) array);
+        }
+    }
+
+```
+### convertToDeclaredCollection
+```java
+    /**
+     * 转换为不同的list对象
+     *
+     * @param config
+     * @param list 数据库查询结果
+     * @param <E>
+     * @return
+     */
+    private <E> Object convertToDeclaredCollection(Configuration config, List<E> list) {
+        //  mybatis ObjectFactory 创建mapper 的返回结果对象
+        Object collection = config.getObjectFactory().create(method.getReturnType());
+        MetaObject metaObject = config.newMetaObject(collection);
+        // metaObject.objectWrapper =>  CollectionWrapper
+        // MetaObject 对象的 objectWrapper 现在是 CollectionWrapper 它是 Collection 的包装
+        metaObject.addAll(list);
+        return collection;
+    }
+
+```
+
+
+- 上述两个为转换的过程,其实质还是在 `org.apache.ibatis.session.SqlSession` 中做执行操作
+
+
+
+## debug 
+- 修改mapper返回数组对`org.apache.ibatis.binding.MapperMethod#convertToArray`方法进行测试
+```java
+    HsSell[] list(@Param("ID") Integer id);
+```
+
+![image-20191219092442456](/images/mybatis/image-20191219092442456.png)
+
+- 修改mapper,对`org.apache.ibatis.binding.MapperMethod#convertToDeclaredCollection`进行测试
+
+  ```java
+      LinkedList<HsSell> list(@Param("ID") Integer id);
+  ```
+
+  
+
+![image-20191219093043035](/images/mybatis/image-20191219093043035.png)
+
+
+
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