Java是一種廣泛應(yīng)用于各個(gè)領(lǐng)域的編程語言，而List和Tree是Java中常用的數(shù)據(jù)結(jié)構(gòu)。在實(shí)際開發(fā)中，我們有時(shí)需要將List數(shù)據(jù)結(jié)構(gòu)轉(zhuǎn)為樹形結(jié)構(gòu)，并將其轉(zhuǎn)為JSON格式輸出。

下面我們來看一個(gè)示例：

public static ListmockDepartments() {
Listdepartments = new ArrayList<>();
Department dep1 = new Department(1, "總部", 0);
Department dep2 = new Department(2, "技術(shù)部", 1);
Department dep3 = new Department(3, "開發(fā)組", 2);
Department dep4 = new Department(4, "測(cè)試組", 2);
Department dep5 = new Department(5, "運(yùn)營部", 1);
Department dep6 = new Department(6, "市場(chǎng)部", 1);
Department dep7 = new Department(7, "銷售部", 6);
departments.add(dep1);
departments.add(dep2);
departments.add(dep3);
departments.add(dep4);
departments.add(dep5);
departments.add(dep6);
departments.add(dep7);
return departments;
}

這段代碼創(chuàng)建了一個(gè)Department對(duì)象的List。我們需要將List轉(zhuǎn)為樹形結(jié)構(gòu)，并將其轉(zhuǎn)為JSON格式輸出。

public static JsonNode listToTree(Listlist, int rootId) {
ObjectNode rootNode = JsonNodeFactory.instance.objectNode();
// 遞歸構(gòu)造樹
buildTree(rootNode, list, rootId);
return rootNode.get("children");
}
public static void buildTree(JsonNode parentNode, Listlist, int parentId) {
ArrayNode childrenNode = JsonNodeFactory.instance.arrayNode();
for (Department department : list) {
if (department.getParentId() == parentId) {
ObjectNode node = JsonNodeFactory.instance.objectNode();
node.put("id", department.getId());
node.put("name", department.getName());
// 遞歸構(gòu)造子樹
buildTree(node, list, department.getId());
childrenNode.add(node);
}
}
// 將子節(jié)點(diǎn)添加到父節(jié)點(diǎn)
if (childrenNode.size() >0) {
((ObjectNode) parentNode).put("children", childrenNode);
}
}

該示例使用了Jackson庫構(gòu)造JSON。代碼首先創(chuàng)建了一個(gè)ObjectNode作為根節(jié)點(diǎn)，然后調(diào)用buildTree()方法遞歸構(gòu)造整棵樹。在buildTree()方法中，首先創(chuàng)建一個(gè)ArrayNode作為子節(jié)點(diǎn)容器，然后遍歷List，找到該節(jié)點(diǎn)的所有子節(jié)點(diǎn)并添加到子節(jié)點(diǎn)容器中。遞歸構(gòu)造子樹后，將子節(jié)點(diǎn)容器添加到父節(jié)點(diǎn)中，并返回子節(jié)點(diǎn)容器。

最后我們將listToTree()方法返回的JsonNode對(duì)象的children字段讀取出來，即可得到完整的樹形JSON。