mybatis paramNameResolver source code

docs/Mybatis/Mybatis-ParamNameResolver.md

@@ -0,0 +1,204 @@
+#  ParamNameResolver 源码解析
+- `org.apache.ibatis.reflection.ParamNameResolver`
+```java
+/**
+ * {@link Param} 注解的扫描工具和处理工具
+ */
+public class ParamNameResolver {
+
+    public static final String GENERIC_NAME_PREFIX = "param";
+
+    /**
+     * <p>
+     * The key is the index and the value is the name of the parameter.<br />
+     * The name is obtained from {@link Param} if specified. When {@link Param} is not specified,
+     * the parameter index is used. Note that this index could be different from the actual index
+     * when the method has special parameters (i.e. {@link RowBounds} or {@link ResultHandler}).
+     * </p>
+     * <ul>
+     * <li>aMethod(@Param("M") int a, @Param("N") int b) -&gt; {{0, "M"}, {1, "N"}}</li>
+     * <li>aMethod(int a, int b) -&gt; {{0, "0"}, {1, "1"}}</li>
+     * <li>aMethod(int a, RowBounds rb, int b) -&gt; {{0, "0"}, {2, "1"}}</li>
+     * </ul>
+     *
+     * {@link ParamNameResolver#ParamNameResolver(org.apache.ibatis.session.Configuration, java.lang.reflect.Method)} 中的map 变量值转换而得
+     * {参数索引: 参数名称(arg0,Param注解的value)}
+     *
+     */
+    private final SortedMap<Integer, String> names;
+
+    private boolean hasParamAnnotation;
+
+    public ParamNameResolver(Configuration config, Method method) {
+        // 方法参数类型
+        final Class<?>[] paramTypes = method.getParameterTypes();
+        // 参数上的注解
+        final Annotation[][] paramAnnotations = method.getParameterAnnotations();
+        //  参数索引和参数名称
+        // {参数索引:参数名称}
+        final SortedMap<Integer, String> map = new TreeMap<>();
+        int paramCount = paramAnnotations.length;
+        // get names from @Param annotations
+        for (int paramIndex = 0; paramIndex < paramCount; paramIndex++) {
+            if (isSpecialParameter(paramTypes[paramIndex])) {
+                // skip special parameters
+                // 如果是特殊类型跳过
+                continue;
+            }
+            String name = null;
+
+            // 注解扫描@Param
+            for (Annotation annotation : paramAnnotations[paramIndex]) {
+                // 是否为 Param 注解的下级
+                if (annotation instanceof Param) {
+                    hasParamAnnotation = true;
+                    // 获取 value 属性值
+                    name = ((Param) annotation).value();
+                    break;
+                }
+            }
+            if (name == null) {
+                // 如果没有写 @param 处理方式如下
+                // @Param was not specified.
+                if (config.isUseActualParamName()) {
+                    name = getActualParamName(method, paramIndex);
+                }
+                if (name == null) {
+                    // use the parameter index as the name ("0", "1", ...)
+                    // gcode issue #71
+                    name = String.valueOf(map.size());
+                }
+            }
+            // 循环参数列表 放入map 对象
+            map.put(paramIndex, name);
+        }
+        names = Collections.unmodifiableSortedMap(map);
+    }
+
+
+    /**
+     * 是否为特殊参数 , 依据 是否是 {@link RowBounds} 或者 {@link  ResultHandler}
+     * @param clazz
+     * @return
+     */
+    private static boolean isSpecialParameter(Class<?> clazz) {
+        return RowBounds.class.isAssignableFrom(clazz) || ResultHandler.class.isAssignableFrom(clazz);
+    }
+
+    /**
+     * 返回方法名  参数索引
+     * @param method
+     * @param paramIndex
+     * @return
+     */
+    private String getActualParamName(Method method, int paramIndex) {
+        return ParamNameUtil.getParamNames(method).get(paramIndex);
+    }
+
+    /**
+     * Returns parameter names referenced by SQL providers.
+     */
+    public String[] getNames() {
+        return names.values().toArray(new String[0]);
+    }
+
+    /**
+     * <p>
+     * A single non-special parameter is returned without a name.
+     * Multiple parameters are named using the naming rule.
+     * In addition to the default names, this method also adds the generic names (param1, param2,
+     * ...).
+     * </p>
+     * <p>
+     * 通常参数异常在这个地方抛出 param ... 异常
+     * 获取参数名称,和参数传递的真实数据
+     */
+    public Object getNamedParams(Object[] args) {
+        final int paramCount = names.size();
+        if (args == null || paramCount == 0) {
+            // 是否有参数
+            return null;
+        } else if (!hasParamAnnotation && paramCount == 1) {
+            // 没有使用 @param 注解 参数只有一个
+            return args[names.firstKey()];
+        } else {
+            // 根据索引创建
+            final Map<String, Object> param = new ParamMap<>();
+            int i = 0;
+            for (Map.Entry<Integer, String> entry : names.entrySet()) {
+                param.put(entry.getValue(), args[entry.getKey()]);
+                // add generic param names (param1, param2, ...)
+                // param + 当前索引位置
+                final String genericParamName = GENERIC_NAME_PREFIX + (i + 1);
+                // ensure not to overwrite parameter named with @Param
+                if (!names.containsValue(genericParamName)) {
+                    param.put(genericParamName, args[entry.getKey()]);
+                }
+                i++;
+            }
+            return param;
+        }
+    }
+}
+
+```
+## debug 阶段
+- 测试用例为同一个 ， 每次修改mapper方法参数来进行debug
+```java
+@Test
+    void testXmlConfigurationLoad() throws IOException {
+        Reader reader = Resources.getResourceAsReader("mybatis-config-demo.xml");
+        SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(reader);
+        Configuration configuration = factory.getConfiguration();
+        SqlSession sqlSession = factory.openSession();
+        HsSellMapper mapper = sqlSession.getMapper(HsSellMapper.class);
+        List<HsSell> list = mapper.list(2);
+        List<Object> objects = sqlSession.selectList("com.huifer.mybatis.mapper.HsSellMapper.list");
+        assertEquals(list.size(), objects.size());
+
+
+    }
+```
+
+
+
+
+```java
+    List<HsSell> list( Integer id);
+
+```
+如果不写`@Param`称则返回
+![image-20191219083223084](assets/image-20191219083223084.png)
+
+```java
+    List<HsSell> list(@Param("ID") Integer id);
+```
+
+- 写`@Param`返回
+
+![image-20191219083344439](/images/mybatis/image-20191219083344439.png)
+
+![image-20191219083354873](/images/mybatis/image-20191219083354873.png)
+
+
+
+- `org.apache.ibatis.reflection.ParamNameResolver#getNamedParams`
+
+  ```java
+      List<HsSell> list( Integer id);
+  ```
+
+![image-20191219084455292](/images/mybatis/image-20191219084455292.png)
+
+  
+
+
+```java
+    List<HsSell> list(@Param("ID") Integer id);
+```
+
+​	写上`@Param`
+
+![image-20191219084943102](/images/mybatis/image-20191219084943102.png)
+
+![image-20191219085131167](/images/mybatis/image-20191219085131167.png)