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docs/Mybatis/HuiFer-Mybatis-MethodSignature.md

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+# MethodSignature
+- `org.apache.ibatis.binding.MapperMethod.MethodSignature`
+```java
+    /**
+     * 方法签名
+     */
+    public static class MethodSignature {
+
+        /**
+         * 返回值是否多个
+         */
+        private final boolean returnsMany;
+        /**
+         * 返回值是不是map
+         */
+        private final boolean returnsMap;
+        /**
+         * 返回值是否 void
+         */
+        private final boolean returnsVoid;
+        /**
+         * 返回的是否是一个游标
+         */
+        private final boolean returnsCursor;
+        /**
+         * 返回值是否是 optional
+         */
+        private final boolean returnsOptional;
+        /**
+         * 返回类型
+         */
+        private final Class<?> returnType;
+        /**
+         * map key
+         */
+        private final String mapKey;
+        private final Integer resultHandlerIndex;
+        private final Integer rowBoundsIndex;
+        /**
+         * 参数解析
+         */
+        private final ParamNameResolver paramNameResolver;
+
+        public MethodSignature(Configuration configuration, Class<?> mapperInterface, Method method) {
+            Type resolvedReturnType = TypeParameterResolver.resolveReturnType(method, mapperInterface);
+            if (resolvedReturnType instanceof Class<?>) {
+                this.returnType = (Class<?>) resolvedReturnType;
+            } else if (resolvedReturnType instanceof ParameterizedType) {
+                this.returnType = (Class<?>) ((ParameterizedType) resolvedReturnType).getRawType();
+            } else {
+                this.returnType = method.getReturnType();
+            }
+            this.returnsVoid = void.class.equals(this.returnType);
+            this.returnsMany = configuration.getObjectFactory().isCollection(this.returnType) || this.returnType.isArray();
+            this.returnsCursor = Cursor.class.equals(this.returnType);
+            this.returnsOptional = Optional.class.equals(this.returnType);
+            this.mapKey = getMapKey(method);
+            this.returnsMap = this.mapKey != null;
+            this.rowBoundsIndex = getUniqueParamIndex(method, RowBounds.class);
+            this.resultHandlerIndex = getUniqueParamIndex(method, ResultHandler.class);
+            this.paramNameResolver = new ParamNameResolver(configuration, method);
+        }
+
+        /**
+         * 方法主要是把方法参数转换为SQL命令参数。
+         *
+         * @param args
+         * @return
+         */
+        public Object convertArgsToSqlCommandParam(Object[] args) {
+            return paramNameResolver.getNamedParams(args);
+        }
+
+        /**
+         * 是否有 {@link RowBounds}
+         *
+         * @return
+         */
+        public boolean hasRowBounds() {
+            return rowBoundsIndex != null;
+        }
+
+        public RowBounds extractRowBounds(Object[] args) {
+            return hasRowBounds() ? (RowBounds) args[rowBoundsIndex] : null;
+        }
+
+        /**
+         * 是否uresultHandler
+         *
+         * @return
+         */
+        public boolean hasResultHandler() {
+            return resultHandlerIndex != null;
+        }
+
+        public ResultHandler extractResultHandler(Object[] args) {
+            return hasResultHandler() ? (ResultHandler) args[resultHandlerIndex] : null;
+        }
+
+        public String getMapKey() {
+            return mapKey;
+        }
+
+        public Class<?> getReturnType() {
+            return returnType;
+        }
+
+        public boolean returnsMany() {
+            return returnsMany;
+        }
+
+        public boolean returnsMap() {
+            return returnsMap;
+        }
+
+        public boolean returnsVoid() {
+            return returnsVoid;
+        }
+
+        public boolean returnsCursor() {
+            return returnsCursor;
+        }
+
+        /**
+         * return whether return type is {@code java.util.Optional}.
+         *
+         * @return return {@code true}, if return type is {@code java.util.Optional}
+         * @since 3.5.0
+         */
+        public boolean returnsOptional() {
+            return returnsOptional;
+        }
+
+        /**
+         * 获取参数名
+         * {@link RowBounds}
+         *
+         * @param method    mapper 方法
+         * @param paramType
+         * @return
+         */
+        private Integer getUniqueParamIndex(Method method, Class<?> paramType) {
+            Integer index = null;
+            // 获取参数类型
+            final Class<?>[] argTypes = method.getParameterTypes();
+            for (int i = 0; i < argTypes.length; i++) {
+                if (paramType.isAssignableFrom(argTypes[i])) {
+                    if (index == null) {
+                        index = i;
+                    } else {
+                        throw new BindingException(method.getName() + " cannot have multiple " + paramType.getSimpleName() + " parameters");
+                    }
+                }
+            }
+            return index;
+        }
+
+        /**
+         * 获取 {@link MapKey} 注解数据
+         *
+         * @param method
+         * @return
+         */
+        private String getMapKey(Method method) {
+            String mapKey = null;
+            if (Map.class.isAssignableFrom(method.getReturnType())) {
+                final MapKey mapKeyAnnotation = method.getAnnotation(MapKey.class);
+                if (mapKeyAnnotation != null) {
+                    mapKey = mapKeyAnnotation.value();
+                }
+            }
+            return mapKey;
+        }
+    }
+
+```