XML and JSON processing in Java

With the continuous development of network technology, XML and JSON have become the two most common data transmission formats. As a mainstream programming language, Java also provides a wealth of XML and JSON processing tools to facilitate developers to parse and generate data. This article will introduce how to use XML and JSON for data processing in Java.

1. XML processing

XML (eXtensible Markup Language) is a markup language used to describe and transmit data. In Java, we can use the following methods to process XML:

1. Java DOM (Document Object Model)

Java DOM is a tree-based structure API (Application Programming Interface) can parse XML documents into a tree structure to facilitate developers to traverse it. The following is a simple Java DOM example:

// 指定XML文件路径
File xmlFile = new File("example.xml");

// 获取DocumentBuilderFactory实例
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();

// 获取DocumentBuilder实例
DocumentBuilder builder = factory.newDocumentBuilder();

// 解析XML文件，生成Document对象
Document document = builder.parse(xmlFile);

// 获取根节点
Element root = document.getDocumentElement();

// 遍历子节点
NodeList nodeList = root.getElementsByTagName("book");
for (int i = 0; i < nodeList.getLength(); i++) {
    Element book = (Element) nodeList.item(i);
    String title = book.getElementsByTagName("title").item(0).getTextContent();
    String author = book.getElementsByTagName("author").item(0).getTextContent();
    String price = book.getElementsByTagName("price").item(0).getTextContent();
    System.out.println("title:" + title + ",author:" + author + ",price:" + price);
}

2. Java SAX (Simple API for XML)

Java SAX is an event-driven API that uses event callbacks way to parse XML files. Compared with Java DOM, Java SAX is more efficient and suitable for processing large XML files. The following is a simple Java SAX example:

// 指定XML文件路径
File xmlFile = new File("example.xml");

// 实例化SAXParserFactory对象
SAXParserFactory factory = SAXParserFactory.newInstance();

// 实例化SAXParser对象
SAXParser parser = factory.newSAXParser();

// 读入XML文件，并处理事件
DefaultHandler handler = new DefaultHandler() {
    boolean title = false;
    boolean author = false;
    boolean price = false;

    public void startElement(String uri, String localName, String qName, Attributes attributes) {
        if (qName.equals("title")) {
            title = true;
        } else if (qName.equals("author")) {
            author = true;
        } else if (qName.equals("price")) {
            price = true;
        }
    }

    public void characters(char[] ch, int start, int length) {
        if (title) {
            System.out.println("title:" + new String(ch, start, length));
            title = false;
        } else if (author) {
            System.out.println("author:" + new String(ch, start, length));
            author = false;
        } else if (price) {
            System.out.println("price:" + new String(ch, start, length));
            price = false;
        }
    }
};

parser.parse(xmlFile, handler);

2. JSON processing

JSON (JavaScript Object Notation) is a lightweight data exchange format that is easy for humans to read and write. It is also easy to parse and generate by machines. In Java, we can use the following methods to process JSON:

1. Java JSONObject

Java JSONObject is a JSON parsing class provided in Java SE 6. Strings or input streams can be parsed to generate JSON objects. Here is a simple Java JSONObject example:

// 定义JSON字符串
String jsonString = "{"name":"Lucy","age":20,"hobby":["reading","music"]}";

// 解析JSON字符串
JSONObject json = new JSONObject(jsonString);

// 获取对象属性
String name = json.getString("name");
int age = json.getInt("age");
JSONArray hobby = json.getJSONArray("hobby");

// 遍历数组
for (int i = 0; i < hobby.length(); i++) {
    System.out.println(hobby.get(i));
}

2. Java GSON

GSON is a Java library provided by Google that can convert JSON strings into Java objects, or Convert Java object to JSON string. The following is a simple Java GSON example:

// 定义JSON字符串
String jsonString = "{"name":"Lucy","age":20,"hobby":["reading","music"]}";

// 解析JSON字符串
Gson gson = new Gson();
User user = gson.fromJson(jsonString, User.class);

// 获取对象属性
String name = user.getName();
int age = user.getAge();
List<String> hobby = user.getHobby();

// 遍历列表
for (String item : hobby) {
    System.out.println(item);
}

Note that the User class here needs to correspond to the format of the JSON string and contain the same attributes and attribute types.

3. Conclusion

Using XML and JSON for data processing in Java allows developers to complete data transmission and analysis more efficiently. Depending on the specific conditions of the data, you can choose Java DOM, Java SAX, Java JSONObject, Java GSON and other related tools for development.

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