将字符串解析为 JsonNode Jackson

17 Mar 2025 | 阅读 2 分钟

在本节中，我们将了解如何使用 Jackson 2.0 将 JSON 字符串转换为 JsonNode。JsonNode 是 Jackson 最常用的类之一。它是一个不可变的类；这意味着我们实际上无法构建 JsonNode 实例的对象图。相反，我们可以创建 JsonNode 的子类（即 ObjectNode）的对象图。

将 JsonString 解析为 JsonNode 的过程非常简单。我们只需创建一个 ObjectMapper 类的实例，并以如下方式使用其 readTree() 方法

String str = "{\"proId\":\"001\",\"proName\":\"MX Pro 20\",\"price\":\"25k\"}";
ObjectMapper map = new ObjectMapper();
JsonNode node = map.readTree(str);

让我们举个例子来理解如何使用 readTree() 方法进行解析。

StringToJsonNodeExample.java

//import required classes and package if any
import java.io.IOException;
import java.text.ParseException;
import com.fasterxml.jackson.core.JsonParseException;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;
//create class StringToJsonNodeExample to understand how to parse string to JsonNode
public class StringToJsonNodeExample {
	//main method start 
	public static void main(String args[]) throws ParseException {
		// create instance of the ObjectSerialization class
		ObjectMapper obj = new ObjectMapper();
		try {
			String jsonString = "{\"proId\":\"001\",\"proName\":\"MX Pro 20\",\"price\":\"25k\"}"; 
			System.out.println(jsonString);
			System.out.println();
			JsonNode node = obj.readTree(jsonString);
			System.out.println("After parsing String to JsonNode: "+node);
			System.out.println();
			JsonNode node1 = node.get("proId");
			System.out.println("Product Id = "+node1.textValue());
			JsonNode node2 = node.get("proName");
			System.out.println("Product Name = "+node2.textValue());
			JsonNode node3 = node.get("price");
			System.out.println("Product Price = "+node3.textValue());
		} catch (JsonParseException e) {
			e.printStackTrace();
		} catch (JsonMappingException e) {
			e.printStackTrace();
		} catch (IOException e) {
			e.printStackTrace();
		} 
	}
}

输出

很多时候，我们需要深入到更底层才能从 JsonString 访问数据。为此，我们使用 JsonFactory、JsonParser、JsonNode 和 getFactory()、createParser() 和 readTree() 方法，如下所示

String str = "{\"proId\":\"001\",\"proName\":\"MX Pro 20\",\"price\":\"25k\"}";
ObjectMapper mapper = new ObjectMapper();
JsonFactory factory = mapper.getFactory();
JsonParser parser = factory.createParser(str);
 JsonNode node = mapper.readTree(parser);

让我们举个例子来理解这三个类及其方法是如何用于解析的。

LowLevelParsingExample.java

//import required classes and package if any
import java.io.IOException;
import java.text.ParseException;
import com.fasterxml.jackson.core.JsonFactory;
import com.fasterxml.jackson.core.JsonParseException;
import com.fasterxml.jackson.core.JsonParser;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;
//create class LowLevelParsingExample to understand how to perform low level parsing
public class LowLevelParsingExample {
	//main method start 
	public static void main(String args[]) throws ParseException {
		// create instance of the ObjectSerialization class
		ObjectMapper obj = new ObjectMapper();
		try {
			String jsonString = "{\"proId\":\"001\",\"proName\":\"MX Pro 20\",\"price\":\"25k\"}"; 
			System.out.println(jsonString);
			System.out.println();
			// create instance of getFactory() method
			JsonFactory factory = obj.getFactory();
			// create parser by using the createParser() method
			JsonParser parser = factory.createParser(jsonString);
			// create JsonNode from parser
			JsonNode node = obj.readTree(parser);
			System.out.println("After parsing String to JsonNode: "+node);
			System.out.println();
			JsonNode node1 = node.get("proId");
			System.out.println("Product Id = "+node1.textValue());
			JsonNode node2 = node.get("proName");
			System.out.println("Product Name = "+node2.textValue());
			JsonNode node3 = node.get("price");
			System.out.println("Product Price = "+node3.textValue());
		} catch (JsonParseException e) {
			e.printStackTrace();
		} catch (JsonMappingException e) {
			e.printStackTrace();
		} catch (IOException e) {
			e.printStackTrace();
		} 
	}
}

输出