如何在Java中将Json节点插入到另一个节点中？

<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-databind</artifactId>
    <version>2.12.4</version>
</dependency>

ObjectMapper objectMapper = new ObjectMapper();
ObjectNode newNode = objectMapper.createObjectNode();
newNode.put("key", "value");

String jsonStr = "{\"name\":\"John\",\"age\":30}";
JsonNode rootNode = objectMapper.readTree(jsonStr);

ObjectNode targetNode = (ObjectNode) rootNode;
targetNode.set("newNode", newNode);

String modifiedJsonStr = objectMapper.writeValueAsString(rootNode);
System.out.println(modifiedJsonStr);