聊聊多层嵌套的json的值如何解析/替换

前言

前阵子承接了2个需求，一个数据脱敏，一个是低代码国际化多语言需求，这两个需求有个共同特点，都是以json形式返回给前端，而且都存在多层嵌套，其中数据脱敏的数据格式是比较固定，而低代码json的格式存在结构固定和不固定 2种格式。最后不管是数据脱敏或者是多语言，业务抽象后，都存在需要做json值替换的需求。今天就来聊下多层嵌套json值如何解析或者替换

多层嵌套json解析

1、方法一：循环遍历+利用正则进行解析

这种做法相对常规，且解析比较繁琐。

2、方法二：利用OGNL表达式

1、何为OGNL

OGNL（Object-Graph Navigation Language）是一种表达式语言，用于在Java应用程序中对对象图进行导航和操作。OGNL本身并不提供直接的执行环境，它是作为一个库或框架的一部分来使用的。因此，OGNL的执行方式取决于使用它的上下文。

一般情况下，OGNL可以通过两种方式执行：解释执行和编译执行。

解释执行：在解释执行中，OGNL表达式在运行时逐条解释和执行。它会在每次表达式执行时动态计算表达式的结果，并根据对象图的实际状态进行导航和操作。这种方式的灵活性较高，可以根据需要对对象图进行动态操作，但相对而言执行效率较低。

编译执行：为了提高执行效率，有些框架会将OGNL表达式编译成可执行的字节码或类文件。在编译执行中，OGNL表达式在编译阶段被转换成可执行代码，然后在运行时直接执行这些生成的代码。这种方式可以在一定程度上提高执行速度，但牺牲了一些灵活性，因为编译后的代码在运行时不再动态计算。

我们经常使用ORM框架mybatis的动态sql解析，它的实现基石就是OGNL表达式。回到正题，我们如何利用OGNL来解析json

a、 在项目POM引入OGNL GAV

 <dependency>
            <groupId>ognl</groupId>
            <artifactId>ognl</artifactId>
            <version>${ognl.version}</version>
        </dependency>

b、 封装OGNL表达式工具类

public final class OgnlCache {

  private static final OgnlMemberAccess MEMBER_ACCESS = new OgnlMemberAccess();
  private static final OgnlClassResolver CLASS_RESOLVER = new OgnlClassResolver();
  private static final Map<String, Object> expressionCache = new ConcurrentHashMap<>();

  private OgnlCache() {
    // Prevent Instantiation of Static Class
  }

  public static Object getValue(String expression, Object root) {
    try {
      Map context = Ognl.createDefaultContext(root, MEMBER_ACCESS, CLASS_RESOLVER, null);
      return Ognl.getValue(parseExpression(expression), context, root);
    } catch (OgnlException e) {
      throw new RuntimeException("Error evaluating expression '" + expression + "'. Cause: " + e, e);
    }
  }

  private static Object parseExpression(String expression) throws OgnlException {
    Object node = expressionCache.get(expression);
    if (node == null) {
      node = Ognl.parseExpression(expression);
      expressionCache.put(expression, node);
    }
    return node;
  }

}

c、 封装json工具类

public final class JsonUtil {

    private JsonUtil(){}

    public static <T> T parse(String jsonStr, Class<T> clazz) throws Exception {
        return JSON.parseObject(jsonStr, clazz);
    }

    public static Object getValue(Map map, String path) throws Exception {
         return OgnlCache.getValue(path,map);
    }
}

d、 多层嵌套json解析例子

private void printMenuI18nCodeByOgnl() throws Exception {
        String menuJson = mockMenuService.getMenuJson();
        Map<String, Object> map = JsonUtil.parse(menuJson, Map.class);
        Object topMenu = JsonUtil.getValue( map,"i18NCode");
        Object userMenu = JsonUtil.getValue( map,"children[0].i18NCode");
        Object userMenuAdd = JsonUtil.getValue( map,"children[0].children[0].i18NCode");
        Object userMenuUpdate = JsonUtil.getValue( map,"children[0].children[1].i18NCode");
        Object deptMenu = JsonUtil.getValue( map,"children[1].i18NCode");
        Object deptMenuList = JsonUtil.getValue( map,"children[1].children[0].i18NCode");
        Object deptMenuDelete = JsonUtil.getValue( map,"children[1].children[1].i18NCode");
        System.out.println(">>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> Print MenuI18nCode By Ognl Start <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<,");
        System.out.println(topMenu);
        System.out.println(userMenu);
        System.out.println(userMenuAdd);
        System.out.println(userMenuUpdate);
        System.out.println(deptMenu);
        System.out.println(deptMenuList);
        System.out.println(deptMenuDelete);
        System.out.println(">>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> Print MenuI18nCode By Ognl End <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<,");
    }

注： 示例中的menuJson形如下

{"children":[{"children":[{"children":[],"component":"saas/index","i18NCode":"user.menu.add","id":8,"linkUrl":"/user/add","menuName":"用户新增","parentId":9,"sort":9999},{"children":[],"component":"saas/index","i18NCode":"user.menu.update","id":7,"linkUrl":"/user/update","menuName":"用户编辑","parentId":9,"sort":9999}],"component":"saas/index","i18NCode":"user.menu","id":9,"linkUrl":"/user","menuName":"用户菜单","parentId":1,"sort":9999},{"children":[{"children":[],"component":"saas/index","i18NCode":"dept.menu.list","id":11,"linkUrl":"/dept/list","menuName":"部门列表","parentId":10,"sort":9999},{"children":[],"component":"saas/index","i18NCode":"dept.menu.delete","id":12,"linkUrl":"/dept/delete","menuName":"部门删除","parentId":10,"sort":9999}],"component":"saas/index","i18NCode":"dept.menu","id":10,"linkUrl":"/dept","menuName":"部门菜单","parentId":1,"sort":9999}],"component":"saas/index","i18NCode":"top.menu","id":1,"linkUrl":"/topUrl","menuName":"顶级菜单","parentId":0,"sort":9999}

解析后控制台打印如下

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> Print MenuI18nCode By Ognl Start <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<,
top.menu
user.menu
user.menu.add
user.menu.update
dept.menu
dept.menu.list
dept.menu.delete
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> Print MenuI18nCode By Ognl End <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<,

3、方法三：留个悬念，待会讲

多层嵌套json替换

1、方法一：循环遍历+正则进行替换

这种做法相对常规，且替换比较繁琐。

2、方法二：利用json类库，进行替换

以fastJSON为例

a、 在项目pom引入fastJSON GAV

 <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>fastjson</artifactId>
            <version>${fastjson.version}</version>
        </dependency>

b、 多层嵌套json替换例子

以将菜单的i18nCode替换为具体语言的值为例

 public String reBuildMenuJson(){
        String orginalMenuJson = getMenuJson();
        JSONObject jsonObject = JSON.parseObject(orginalMenuJson);
        jsonObject.put(I18N_CODE_COLUMN,mockI18nCache.get(jsonObject.get(I18N_CODE_COLUMN)));
        reBuildChildJson(jsonObject);
        return JSON.toJSONString(jsonObject);

    }

    private void reBuildChildJson(JSONObject curentObject){
        JSONArray children = curentObject.getJSONArray(CHILDREN_COLUMN);
        for (int i = 0; i < children.size(); i++) {
            JSONObject child = children.getJSONObject(i);
            child.put(I18N_CODE_COLUMN,mockI18nCache.get(child.get(I18N_CODE_COLUMN)));
            reBuildChildJson(child);
        }

    }

注： 未替换前，menuJson形如下

{"children":[{"children":[{"children":[],"component":"saas/index","i18NCode":"user.menu.add","id":8,"linkUrl":"/user/add","menuName":"用户新增","parentId":9,"sort":9999},{"children":[],"component":"saas/index","i18NCode":"user.menu.update","id":7,"linkUrl":"/user/update","menuName":"用户编辑","parentId":9,"sort":9999}],"component":"saas/index","i18NCode":"user.menu","id":9,"linkUrl":"/user","menuName":"用户菜单","parentId":1,"sort":9999},{"children":[{"children":[],"component":"saas/index","i18NCode":"dept.menu.list","id":11,"linkUrl":"/dept/list","menuName":"部门列表","parentId":10,"sort":9999},{"children":[],"component":"saas/index","i18NCode":"dept.menu.delete","id":12,"linkUrl":"/dept/delete","menuName":"部门删除","parentId":10,"sort":9999}],"component":"saas/index","i18NCode":"dept.menu","id":10,"linkUrl":"/dept","menuName":"部门菜单","parentId":1,"sort":9999}],"component":"saas/index","i18NCode":"top.menu","id":1,"linkUrl":"/topUrl","menuName":"顶级菜单","parentId":0,"sort":9999}

替换后，menuJson形如下

{"component":"saas/index","children":[{"component":"saas/index","children":[{"component":"saas/index","children":[],"linkUrl":"/user/add","menuName":"用户新增","id":8,"sort":9999,"i18NCode":"userMenuAdd","parentId":9},{"component":"saas/index","children":[],"linkUrl":"/user/update","menuName":"用户编辑","id":7,"sort":9999,"i18NCode":"userUpdateAdd","parentId":9}],"linkUrl":"/user","menuName":"用户菜单","id":9,"sort":9999,"i18NCode":"userMenu","parentId":1},{"component":"saas/index","children":[{"component":"saas/index","children":[],"linkUrl":"/dept/list","menuName":"部门列表","id":11,"sort":9999,"i18NCode":"deptMenuList","parentId":10},{"component":"saas/index","children":[],"linkUrl":"/dept/delete","menuName":"部门删除","id":12,"sort":9999,"i18NCode":"deptMenuDelete","parentId":10}],"linkUrl":"/dept","menuName":"部门菜单","id":10,"sort":9999,"i18NCode":"deptMenu","parentId":1}],"linkUrl":"/topUrl","menuName":"顶级菜单","id":1,"sort":9999,"i18NCode":"topMenu","parentId":0}

3、方法三：利用json序列化注解

以菜单国际化为示例

1、自定义注解

@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
@JacksonAnnotationsInside
@JsonSerialize(using = I18nJsonSerializer.class)
public @interface I18nField {


}

2、自定义国际化翻译接口（该具体实现留给业务扩展）

public interface I18nService {

    String getTargetContent(String i18nCode);
}

题外话 ： 为啥不像spring的messageSource定义成

	String getMessage(String code, @Nullable Object[] args, @Nullable String defaultMessage, Locale locale);

因为很多参数信息可以直接通过上下文获取，比如Locale可以通过LocaleContextHolder.getLocale()

3、编写json序列化接口

public class I18nJsonSerializer extends JsonSerializer<String> implements ContextualSerializer {

    @Autowired
    private I18nService i18nService;
    @Override
    public void serialize(String s, JsonGenerator jsonGenerator, SerializerProvider serializerProvider) throws IOException {
        jsonGenerator.writeString(i18nService.getTargetContent(s));

    }

    @Override
    public JsonSerializer<?> createContextual(SerializerProvider serializerProvider, BeanProperty beanProperty) throws JsonMappingException {

        I18nField i18nField = beanProperty.getAnnotation(I18nField.class);

        if(!ObjectUtils.isEmpty(i18nField) && String.class.isAssignableFrom(beanProperty.getType().getRawClass())){
            return this;
        }
        return serializerProvider.findValueSerializer(beanProperty.getType(),beanProperty);
    }
}

4、定义和json字段能够匹配的对象

大白话，就是json和这个对象可以相互转换。以菜单为例

@Data
@EqualsAndHashCode(callSuper = true, of = {"id"})
public class MenuResourceDTO extends TreeDTO<MenuResourceDTO> implements Serializable {

    private static final long serialVersionUID = 1L;

 。。。。。省略其他属性
    /**
     * 单菜名称
     */
    private String menuName;

  
    private String permission;
    /**
     * 是否缓存
     */
    private Integer keepAlive;

    @I18nField
    private String i18NCode;


    public static String I18N_CODE_COLUMN = "i18NCode";
    public static String CHILDREN_COLUMN = "children";

5、在需要进行替换的字段上加上 @I18nField注解

   @I18nField
    private String i18NCode;

6、替换验证

编写一个测试controller，用来输出替换后的菜单信息

@RestController
@RequestMapping("menu")
@RequiredArgsConstructor
public class MockMenuController {

    private final MockMenuService mockMenuService;


    @GetMapping
    public MenuResourceDTO getMenu(){
        return mockMenuService.getMenuResourceDTO();
    }
}

通过POSTMAN访问，得到如下信息

{
    "id": 1,
    "parentId": 0,
    "sort": 9999,
    "children": [
        {
            "id": 9,
            "parentId": 1,
            "sort": 9999,
            "children": [
                {
                    。。。省略其他信息
                    "menuName": "用户新增",
                    "i18NCode": "userMenuAdd"
                },
                {
                    。。。省略其他信息
                    "menuName": "用户编辑",
                    "i18NCode": "userUpdateAdd"
                }
            ],
            。。。省略其他信息
            "menuName": "用户菜单",
            "i18NCode": "userMenu"
        },
    "menuName": "顶级菜单",
    "i18NCode": "topMenu"
}

回答上面多层json解析的方法三，那个悬念做法就是将json与对象映射起来，通过对象来取值

4、方法四：先自己发散下，然后看下总结

总结

本文的多层嵌套json的解析和替换都提供了几种方案，综合来讲是推荐将json先转对象，通过对象操作。对json替换，推荐使用自定义json序列化注解的方式。但这种方式比较适合json的结构以及字段是固定的方式。对于低代码，本身的json结构是多种多样的，如果要后端实现，一种做法，就是将这些json都映射成对象，但因为json结构多种多样，就会导致要映射的对象膨胀。另一种方式，是直接转JsonObject，通过JsonObject来操作替换

其次现在都是前后端分离，有些东西其实也可以放在前端实现，比如这种替换工作其实挺适合放在前端做的。以低代码为例，因为前端本来就需要解析json，后端可以维护一个映射表，前端实现一个组件函数，通过该函数优先从前端缓存取，取不到再从调用后端接口，这就是json替换的方法四，把替换工作留给前端做，哈哈。大家是一个团队，哪边好实现，就放哪边做

最后那个ognl的代码，我是直接把mybatis的源码搬过来，直接套用了。开源有的东西，就没必要自己再搞一遍了