使用 Jackson 递归地构建一个 JSON 字符串到 jsTree

Question

我一直在尝试使用 Jackson 库（v.1.7.4，这是我唯一可以用于此项目的库）在 Java 中构建一个 JSON 字符串，以jsTree 接受的格式 (https://www.jstree.com/docs/json/)。我只关心 "text" 和 "children" 属性。问题是，我没有得到一个可行的递归方法来这样做。

如果我有一棵像这样的简单树：

    Tree<String> tree = new Tree<String>();
    Node<String> rootNode = new Node<String>("root");
    Node<String> nodeA = new Node<String>("A");
    Node<String> nodeB = new Node<String>("B");
    Node<String> nodeC = new Node<String>("C");
    Node<String> nodeD = new Node<String>("D");
    Node<String> nodeE = new Node<String>("E");

    rootNode.addChild(nodeA);
    rootNode.addChild(nodeB);
    nodeA.addChild(nodeC);
    nodeB.addChild(nodeD);
    nodeB.addChild(nodeE);

    tree.setRootElement(rootNode);

我希望我的字符串是：

 {text: "root", children: [{text:"A", children:[{text:"C", children: []}]}, {text:"B", children: [{text: "D", children: []}, {text:"E", children:[]}]}] }

我正在尝试使用 Jackson 的树模型构建 JSON 字符串。到目前为止，我的代码看起来像这样：

 public String generateJSONfromTree(Tree<String> tree) throws IOException{
    String json = "";

    ObjectMapper mapper = new ObjectMapper();
    JsonFactory factory = new JsonFactory();
    ByteArrayOutputStream out = new ByteArrayOutputStream(); // buffer to write to string later
    JsonGenerator generator = factory.createJsonGenerator(out, JsonEncoding.UTF8);

    JsonNode rootNode = mapper.createObjectNode();
    JsonNode coreNode = mapper.createObjectNode();          

    JsonNode dataNode = (ArrayNode)generateJSON(tree.getRootElement()); // the tree nodes

    // assembly arrays and objects
    ((ObjectNode)coreNode).put("data", dataNode);
    ((ObjectNode)rootNode).put("core", coreNode);       
    mapper.writeTree(generator, rootNode);

    json  = out.toString();
    return json;
}

 public ArrayNode generateJSON(Node<String> node, ObjectNode obN, ArrayNode arrN){
    // stop condition ?
    if(node.getChildren().isEmpty()){
        arrN.add(obN);
        return arrN;
    }

    obN.put("text", node.getData());
    for (Node<String> child : node.getChildren()){

        // recursively call on child nodes passing the current object node
        obN.put("children", generateJSON(child, obN, arrN));
    }

}

我尝试了一些变体，但到目前为止没有成功。我知道答案可能比我尝试的要简单，但我卡住了。也许停止条件不合适或逻辑本身（我的想法是尝试在下一次调用时重用 ObjectNode 和 ArrayNode 对象，"insert" "children" 元素（来自 json ) 在树的下一个子节点上，所以它会向后构建，但最后我得到空变量 )。

我的树和节点类基于以下内容：http://sujitpal.blogspot.com.br/2006/05/java-data-structure-generic-tree.html

Answer 1

不是最好的方法，但它完成了工作：

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.util.Iterator;

import com.fasterxml.jackson.core.JsonEncoding;
import com.fasterxml.jackson.core.JsonFactory;
import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.node.ArrayNode;
import com.fasterxml.jackson.databind.node.ObjectNode;

public class TreeApp {

    public String generateJSONfromTree(Tree<String> tree) throws IOException {
        ObjectMapper mapper = new ObjectMapper();
        JsonFactory factory = new JsonFactory();
        ByteArrayOutputStream out = new ByteArrayOutputStream(); // buffer to write to string later
        JsonGenerator generator = factory.createJsonGenerator(out, JsonEncoding.UTF8);

        ObjectNode rootNode = generateJSON(tree.getRootElement(), mapper.createObjectNode());
        mapper.writeTree(generator, rootNode);

        return out.toString();
    }

    public ObjectNode generateJSON(Node<String> node, ObjectNode obN) {
        if (node == null) {
            return obN;
        }

        obN.put("text", node.getData());

        ArrayNode childN = obN.arrayNode();
        obN.set("children", childN);        
        if (node.getChildren() == null || node.getChildren().isEmpty()) {
            return obN;
        }

        Iterator<Node<String>> it = node.getChildren().iterator();
        while (it.hasNext()) {  
            childN.add(generateJSON(it.next(), new ObjectMapper().createObjectNode()));
        }
        return obN;
    }

    public static void main(String[] args) throws IOException {
        Tree<String> tree = new Tree<String>();
        Node<String> rootNode = new Node<String>("root");
        Node<String> nodeA = new Node<String>("A");
        Node<String> nodeB = new Node<String>("B");
        Node<String> nodeC = new Node<String>("C");
        Node<String> nodeD = new Node<String>("D");
        Node<String> nodeE = new Node<String>("E");

        rootNode.addChild(nodeA);
        rootNode.addChild(nodeB);
        nodeA.addChild(nodeC);
        nodeB.addChild(nodeD);
        nodeB.addChild(nodeE);

        tree.setRootElement(rootNode);

        System.out.println(new TreeApp().generateJSONfromTree(tree));
    }
}

使用 Jackson 递归地构建一个 JSON 字符串到 jsTree

Recursively building a JSON string to jsTree with Jackson

java

json

recursion

jackson

jstree