擴展fastjson的SimplePropertyPreFilter，以過濾不需要序列化的屬性

版權聲明：本文爲博主原創文章，但是你也可以隨意轉載。 https://blog.csdn.net/smartcore/article/details/80106538

java應用在進行系統間通信時，經常會使用json格式進行數據傳輸交換。利用alibaba fastjson（本文使用的是1.2.46），對象與json字符串的相互轉換非常的便利。

但是，在對對象進行json序列化時，經常會出現以下的場景：對象的類是一個與數據庫表相關的業務實體類，如以下實體類：

public class DiagramEntity {
    private String name;
    private String code;
    private int beginDate;
    private int endDate;
    private int flag;
    private String createId;
    private int createDate;

    // 訪問器定義
}

其對應的數據庫表字段如下：

字段名	類型
name	varchar(36)
code	varchar(36)
beginDate	Integer
endDate	Integer
flag	Integer
createId	varchar(36)
createDate	Integer

然而，在向客戶端或者對手系統傳輸數據時，我們可能會在運行時選擇性的進行某些屬性的傳輸，比如對以上的類，僅需要傳輸name、code、beginDate、endDate，其餘的屬性不需要傳輸。遇到此種情況我們可以使用fastjson提供的com.alibaba.fastjson.serializer.SimplePropertyPreFilter類，創建一個此類的對象，然後利用其getExcludes()方法，添加不需要進行序列化的屬性。

爲了更加的方便使用過濾屬性，本文對SimplePropertyPreFilter類進行了微小擴展，實現了SimplePropertyPreFilterEx類，在後者中增加了一個帶三個參數的構造函數：

public SimplePropertyPreFilterEx(Class<?> clazz, String[] includeProperties, String[] excludeProperties);

以更方便的設置序列化時包含或者排除的屬性。如以下使用：

@Test
public void testJsonExcludes() {
    SimplePropertyPreFilterEx objFilter = new SimplePropertyPreFilterEx(null, null,
            new String[] {"flag", "createId", "createDate"});

    DiagramEntity objMessage = new DiagramEntity();
    objMessage.setName("張三三");
    objMessage.setCode("X001");

    String strRet = JSON.toJSONString(objMessage, objFilter);
    System.out.println(strRet);
}

輸出結果：

{"beginDate":0,"code":"X001","endDate":0,"name":"張三三"}

附：SimplePropertyPreFilterEx類定義示例：

package com.bn.zbase.message.util;

/**
 * Copyright 1999-2017 Alibaba Group.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import com.alibaba.fastjson.serializer.SimplePropertyPreFilter;
import java.util.Collections;

public class SimplePropertyPreFilterEx extends SimplePropertyPreFilter {
    public SimplePropertyPreFilterEx(String... includeProperties){
        super(null, includeProperties);
    }

    public SimplePropertyPreFilterEx(Class<?> clazz, String... includeProperties){
        super(clazz, includeProperties);
    }

    public SimplePropertyPreFilterEx(Class<?> clazz, String[] includeProperties, String[] excludeProperties) {
        super(clazz, includeProperties == null ? new String[0] : includeProperties);
        if (excludeProperties != null && excludeProperties.length > 0) {
            Collections.addAll(getExcludes(), excludeProperties);
        }
    }
}