Fastjson - 自定义过滤器（PropertyPreFilter）

SerializeFilter是通过编程扩展的方式定制序列化。Fastjson 支持6种 SerializeFilter，用于不同场景的定制序列化。

• PropertyPreFilter：根据 PropertyName 判断是否序列化

• PropertyFilter：根据 PropertyName 和 PropertyValue 来判断是否序列化

• NameFilter：修改 Key，如果需要修改 Key，process 返回值则可

• ValueFilter：修改 Value

• BeforeFilter：序列化时在最前添加内容

• AfterFilter：序列化时在最后添加内容

1. 需求

JSON 数据格式如下，需要过滤掉其中 "book" 的 "price" 属性。

JSON数据格式：

{
  "store": {
    "book": [
      {
        "category": "reference","author": "Nigel Rees","title": "Sayings of the Century","price": 8.95
      },{
        "category": "fiction","author": "Evelyn Waugh","title": "Sword of Honour","price": 12.99
      }
    ],"bicycle": {
      "color": "red","price": 19.95
    }
  },"expensive": 10
}

2. SimplePropertyPreFilter 过滤器

该过滤器由Fastjson 提供，代码实现：

String json = "{"store":{"book":[{"category":"reference","author":"Nigel Rees","title":"Sayings of the Century","price":8.95},{"category":"fiction","author":"Evelyn Waugh","title":"Sword of Honour","price":12.99}],"bicycle":{"color":"red","price":19.95}},"expensive":10}";
SimplePropertyPreFilter filter = new SimplePropertyPreFilter();
filter.getExcludes().add("price");
JSONObject jsonObject = JSON.parSEObject(json);
String str = JSON.toJSONString(jsonObject,filter);
System.out.println(str);

运行结果：

{
  "store": {
    "bicycle": {
      "color": "red"
    },"book": [
      {
        "author": "Nigel Rees","category": "reference","title": "Sayings of the Century"
      },{
        "author": "Evelyn Waugh","category": "fiction","title": "Sword of Honour"
      }
    ]
  },"expensive": 10
}

查看 JSON 数据的过滤结果，发现 "bicycle" 中的 "price" 属性也被过滤掉了，不符合需求。

3. LevelPropertyPreFilter 过滤器

该自定义过滤器实现 PropertyPreFilter 接口，实现根据层级过滤 JSON 数据中的属性。
扩展类：

/**
 * 层级属性删除
 * 
 * @author yinjianwei
 * @date 2017年8月24日 下午3:55:19
 *
 */
public class LevelPropertyPreFilter implements PropertyPreFilter {

    private final Class<?> clazz;
    private final Set<String> includes = new HashSet<String>();
    private final Set<String> excludes = new HashSet<String>();
    private int maxLevel = 0;

    public LevelPropertyPreFilter(String... properties) {
        this(null,properties);
    }

    public LevelPropertyPreFilter(Class<?> clazz,String... properties) {
        super();
        this.clazz = clazz;
        for (String item : properties) {
            if (item != null) {
                this.includes.add(item);
            }
        }
    }

    public LevelPropertyPreFilter addExcludes(String... filters) {
        for (int i = 0; i < filters.length; i++) {
            this.getExcludes().add(filters[i]);
        }
        return this;
    }

    public LevelPropertyPreFilter addIncludes(String... filters) {
        for (int i = 0; i < filters.length; i++) {
            this.getIncludes().add(filters[i]);
        }
        return this;
    }

    public boolean apply(JSONSerializer serializer,Object source,String name) {
        if (source == null) {
            return true;
        }

        if (clazz != null && !clazz.isInstance(source)) {
            return true;
        }

        // 过滤带层级属性（store.book.price）
        SerialContext serialContext = serializer.getContext();
        String levelName = serialContext.toString();
        levelName = levelName + "." + name;
        levelName = levelName.replace("$.","");
        levelName = levelName.replaceAll("[d+]","");
        if (this.excludes.contains(levelName)) {
            return false;
        }

        if (maxLevel > 0) {
            int level = 0;
            SerialContext context = serializer.getContext();
            while (context != null) {
                level++;
                if (level > maxLevel) {
                    return false;
                }
                context = context.parent;
            }
        }

        if (includes.size() == 0 || includes.contains(name)) {
            return true;
        }

        return false;
    }

    public int getMaxLevel() {
        return maxLevel;
    }

    public void setMaxLevel(int maxLevel) {
        this.maxLevel = maxLevel;
    }

    public Class<?> getClazz() {
        return clazz;
    }

    public Set<String> getIncludes() {
        return includes;
    }

    public Set<String> getExcludes() {
        return excludes;
    }
}

代码实现：

public static void main(String[] args) {
    String json = "{"store":{"book":[{"category":"reference","expensive":10}";
    JSONObject jsonObj = JSON.parSEObject(json);
    LevelPropertyPreFilter propertyPreFilter = new LevelPropertyPreFilter();
    propertyPreFilter.addExcludes("store.book.price");
    String json2 = JSON.toJSONString(jsonObj,propertyPreFilter);
    System.out.println(json2);
}

运行结果：

{
  "store": {
    "bicycle": {
      "color": "red","price": 19.95
    },"expensive": 10
}

查看 JSON 数据的过滤结果，实现了上面的需求。

参考：http://www.cnblogs.com/dirgo/...

（编辑：李大同）

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