【Java123】XML与JSON互相转化

 http://www.bejson.com/json2javapojo/new/

https://www.cnblogs.com/111testing/p/9162229.html

https://wenku.baidu.com/view/8364d04b86c24028915f804d2b160b4e777f8102.html

https://www.jianshu.com/p/8dadd9a232b1

使用org.json的Demo：

import org.apache.commons.io.IOUtils;
import org.json.JSONException;
import org.json.JSONObject;
import org.json.XML;

import java.io.IOException;
import java.io.InputStream;

public class XML2JSON {

    public XML2JSON(){}

    public static String xml2jsonString(String  filepath) throws IOException, JSONException {

        InputStream in = XML2JSON.class.getResourceAsStream(filepath);
        String xml = IOUtils.toString(in);
        System.out.print(xml);
        System.out.println();

        JSONObject xmlJSONObj = XML.toJSONObject(xml);
        String jsonStr = xmlJSONObj.toString();
        System.out.print(jsonStr);

        return xmlJSONObj.toString();

    }


    public static void main(String[] args) throws JSONException, IOException {

        String string = xml2jsonString("simple.xml");
        System.out.println(string);

    }

}

测试1：

<?xml version="1.0" encoding="ISO-8859-1"?>

<current_observation>

 <book id="bk101">
  <author>Gambardella, Matthew</author>
  <title>XML Developer's Guide</title>
  <genre>Computer</genre>
  <price>44.95</price>
  <publish_date>2000-10-01</publish_date>
  <description>An in-depth look at creating applications
   with XML.</description>
 </book>

 <book id="bk102">
 <author>Ralls, Kim</author>
 <title>Midnight Rain</title>
 <credit>NOAA's National Weather Service</credit>
 <credit_URL>http://weather.gov/</credit_URL>
 </book>

 <image>
  <url>http://weather.gov/images/xml_logo.gif</url>
  <title>NOAA's National Weather Service</title>
  <link>http://weather.gov</link>
 </image>

 <location>New York/John F. Kennedy Intl Airport, NY</location>
 <station_id>KJFK</station_id>
 <latitude>40.66</latitude>
 <longitude>-73.78</longitude>
 <observation_time_rfc822>
  Mon, 11 Feb 2008 06:51:00 -0500 EST
 </observation_time_rfc822>

 <weather>A Few Clouds</weather>
 <temp_f>11</temp_f>
 <temp_c>-12</temp_c>
 <relative_humidity>36</relative_humidity>
 <wind_dir>West</wind_dir>
 <wind_degrees>280</wind_degrees>
 <wind_mph>18.4</wind_mph>
 <wind_gust_mph>29</wind_gust_mph>
 <pressure_mb>1023.6</pressure_mb>
 <pressure_in>30.23</pressure_in>
 <dewpoint_f>-11</dewpoint_f>
 <dewpoint_c>-24</dewpoint_c>
 <windchill_f>-7</windchill_f>
 <windchill_c>-22</windchill_c>
 <visibility_mi>10.00</visibility_mi>

 <icon_url_base>
  http://weather.gov/weather/images/fcicons/
 </icon_url_base>
 <icon_url_name>nfew.jpg</icon_url_name>
 <two_day_history_url>
  http://www.weather.gov/data/obhistory/KJFK.html
 </two_day_history_url>
 <disclaimer_url>
  http://weather.gov/disclaimer.html
 </disclaimer_url>
 <copyright_url>
  http://weather.gov/disclaimer.html
 </copyright_url>

</current_observation>

 

{"current_observation":{"copyright_url":"http://weather.gov/disclaimer.html","windchill_f":-7,"windchill_c":-22,"book":[{"author":"Gambardella, Matthew","price":44.95,"genre":"Computer","description":"An in-depth look at creating applications with XML.","id":"bk101","title":"XML Developer's Guide","publish_date":"2000-10-01"},{"author":"Ralls, Kim","credit_URL":"http://weather.gov/","id":"bk102","title":"Midnight Rain","credit":"NOAA's National Weather Service"}],"latitude":40.66,"two_day_history_url":"http://www.weather.gov/data/obhistory/KJFK.html","temp_c":-12,"temp_f":11,"wind_mph":18.4,"wind_degrees":280,"icon_url_base":"http://weather.gov/weather/images/fcicons/","icon_url_name":"nfew.jpg","weather":"A Few Clouds","dewpoint_f":-11,"longitude":-73.78,"image":{"link":"http://weather.gov","title":"NOAA's National Weather Service","url":"http://weather.gov/images/xml_logo.gif"},"dewpoint_c":-24,"station_id":"KJFK","wind_dir":"West","pressure_in":30.23,"wind_gust_mph":29,"disclaimer_url":"http://weather.gov/disclaimer.html","location":"New York/John F. Kennedy Intl Airport, NY","relative_humidity":36,"pressure_mb":1023.6,"visibility_mi":10,"observation_time_rfc822":"Mon, 11 Feb 2008 06:51:00 -0500 EST"}}

测试2：

<?xml version="1.0" encoding="ISO-8859-1"?>
<!-- Edited with XML Spy v2007 (http://www.altova.com) -->
<current_observation>

 <book/>

 <book></book>

 <book id="bk98"/>

 <book id="bk99">Hello World!</book>

 <book id="bk100">
  <author>Helen</author>
  <author>Jason</author>
 </book>

 <book id="bk101">
  <author>Gambardella, Matthew</author>
  <title>XML Developer's Guide</title>
  <genre>Computer</genre>
  <price>44.95</price>
  <publish_date>2000-10-01</publish_date>
  <description>An in-depth look at creating applications
   with XML.</description>
 </book>

 <book id="bk102">
 <author>Ralls, Kim</author>
 <title>Midnight Rain</title>
 <credit>NOAA's National Weather Service</credit>
 <credit_URL>http://weather.gov/</credit_URL>
 </book>

</current_observation>

{"current_observation":{"book":["","",{"id":"bk98"},{"id":"bk99","content":"Hello World!"},{"author":["Helen","Jason"],"id":"bk100"},{"author":"Gambardella, Matthew","price":44.95,"genre":"Computer","description":"An in-depth look at creating applications with XML.","id":"bk101","title":"XML Developer's Guide","publish_date":"2000-10-01"},{"author":"Ralls, Kim","credit_URL":"http://weather.gov/","id":"bk102","title":"Midnight Rain","credit":"NOAA's National Weather Service"}]}}

对比在线转换

http://www.bejson.com/xml2json/

JSON转换结果对比上边有几点不同：

1. 忽略无意义的book数据

 <book/>

 <book></book>

2. 缺省key值为#text

{
  "current_observation": {
    "book": [
      { "-id": "bk98" },
      {
        "-id": "bk99",
        "#text": "Hello World!"
      },
      {
        "-id": "bk100",
        "author": [
          "Helen",
          "Jason"
        ]
      },
      {
        "-id": "bk101",
        "author": "Gambardella, Matthew",
        "title": "XML Developer's Guide",
        "genre": "Computer",
        "price": "44.95",
        "publish_date": "2000-10-01",
        "description": "An in-depth look at creating applications
   with XML."
      },
      {
        "-id": "bk102",
        "author": "Ralls, Kim",
        "title": "Midnight Rain",
        "credit": "NOAA's National Weather Service",
        "credit_URL": "http://weather.gov/"
      }
    ]
  }
}

各路方法，有使用第三方API，或者自写遍历迭代方法。

在针对上述Demo的测试结果做分析，还需要进一步考虑以下几点：

1. 源XML文件自身特殊及复杂情况的转换定义。比如，字段含特殊字符，一个标签含多个属性，多个标签同名，invalid file等。

2. 目标JSON文件的转换定义。比如，各元素是否保持原有顺序，多个同名标签作为数组还是同级对象，等。

3. 转换过程中的异常处理。比如，转换中遇到无法解析而跳出导致该目标文件无效，异常捕获记录，等。

https://blog.csdn.net/bestxiaok/article/details/80443640

还有一个如何测试转换生成的JSON文件是否“正确”?

1. 是否是一个合格的JSON文件？

Why Validate Data as a Separate Step?

• to fail fast
• to avoid data corruption
• to simplify processing code
• to use validation code in tests

比较完备但复杂的做法：使用预定义的JSON-Schema来校验文件

• https://github.com/java-json-tools/json-schema-validator

比较简单直接的做法：使用库加载JSON文件时抛出的异常来判断

2. 如何将测试预期结果JSON文件和待测JSON文件进行比对？（Github上只关注了Java）

• https://github.com/fslev/json-compare
• https://github.com/a2design-inc/json-compare

项目实践中，采用JAXB的Marshaller实现xml到java object的反序列化，再序列化为json时候默认空value=null, 空数组=[]，空对象为{}

测试时候，无法直接使用xml->json的处理，因为空属性的加入，无法无中生有，所以只好也走一套反序列化到序列化的流程。代价就是不得不使用项目的java object或者构建一套测试自己的Dao层.....如果时复杂java object的话，本身变动频繁，后期维护代价很大。另一套方案是测试比较结果的处理，无中生有的空字段比较设立ignore list，如有对象变动，仅需更新ignore list即可，但若实现caseBycase Ignore的处理，case处理情况爆炸，代价又太大。

真的是测试要考虑的比代码本身还复杂。。。若测试引入的代码过多，是否有悖初衷呢？

实际项目用三种途径实现XML到JSON的转换。

一、XML->JSON

        JSONObject xmlJSONObj = XML.toJSONObject(xml);
        String jsonStr = xmlJSONObj.toString();

二、XML->JavaBean

JAXB

Create - UserJavaBeanClass

    public static Object xmlToBean(String xmlPath,Class<?> load) throws JAXBException, IOException {

        LocalFileResourceParser fileLoader = new LocalFileResourceParser();
        InputStream in = fileLoader.parseFile(xmlPath);

        JAXBContext context = JAXBContext.newInstance(load);
        Unmarshaller unmarshaller = context.createUnmarshaller();
        Object object = unmarshaller.unmarshal(in);
        return object;
    }

三、JavaBean->JSON

(1) Gson

// https://mvnrepository.com/artifact/org.json/json
compile group: 'org.json', name: 'json', version: '20160810'

        Gson gson = new GsonBuilder().serializeNulls().create();
        String jsonStr = gson.toJson(metadata);

(2) fastjson

// https://mvnrepository.com/artifact/com.alibaba/fastjson
compile group: 'com.alibaba', name: 'fastjson', version: '1.2.54'

public class BeanToJson {

    private static final SerializerFeature[] features = {
                SerializerFeature.PrettyFormat, // JSON标准格式化输出
                SerializerFeature.NotWriteRootClassName, //
                SerializerFeature.WriteClassName, //
                SerializerFeature.SortField, //
                SerializerFeature.WriteMapNullValue, // 输出空置字段
                SerializerFeature.WriteNullListAsEmpty, // list字段如果为null，输出为[]，而不是null
                // SerializerFeature.WriteNullNumberAsZero, // 数值字段如果为null，输出为0，而不是null
                // SerializerFeature.WriteNullBooleanAsFalse, // Boolean字段如果为null，输出为false，而不是null
                // SerializerFeature.WriteNullStringAsEmpty, // 字符类型字段如果为null，输出为""，而不是null
                SerializerFeature.WriteDateUseDateFormat // 日期格式化yyyy-MM-dd HH:mm:ss
    };

    public static String toJsonString (Object object) throws JSONException {
        String jsonStr = JSON.toJSONString(object, true);
        return jsonStr;
    }

    public static String toJsonStringWithFeature (Object object) throws JSONException {
        String jsonStr = JSON.toJSONString(object, BeanToJson.features);
        return jsonStr;
    }

}

比较：

gson可以设置某些feature，若要实现更复杂的feature，需要自己实现。

fastjson可以设置更多的features，满足项目需要。