Jackson高级操作————节点树

引言

继《Jackson快速入门》基础篇之后的树模型相关操作。

节点树模型

ObjectMapper构建JsonNode节点树，类似于DOM解析器的XML。

    @Testpublic void testJsonTree() throws JsonProcessingException, IOException {String jsonString = "{\"name\":\"Tom\", \"age\":25,\"isTeacher\":false,\"marks\": [100,90,85],\"father\" : {\"name\" : \"Jack\", \"age\" : 45}}";JsonNode jsonNode = mapper.readTree(jsonString);System.out.println("----" + jsonNode);/* 遍历节点名称*/Iterator<String> fieldNames = jsonNode.fieldNames();while (fieldNames.hasNext()) {System.out.println(fieldNames.next());}System.out.println("----------------");/* 遍历节点属性值*/Iterator<JsonNode> elements = jsonNode.elements();while (elements.hasNext()) {System.out.println(elements.next());}System.out.println("----------------");/* 获取指定节点属性值*//* get(int index)for accessing value of the specified element of an array node. * For other nodes, null is always returned.*/JsonNode path = jsonNode.get("marks").get(0);System.out.println(path);}

输出结果：

树到Json转换

    @Testpublic void testTree2Json() throws JsonGenerationException, JsonMappingException, IOException {ArrayNode marksNode = mapper.createArrayNode();marksNode.add(100);marksNode.add(90);marksNode.add(50);ObjectNode rootNode = mapper.createObjectNode();rootNode.put("name", "Tom");rootNode.put("age", 21);rootNode.set("verified", marksNode);// 序列化到Tom.json文件中mapper.writeValue(new File("Tom.json"), rootNode);// 从文件中再读取回来JsonNode treeNode = mapper.readTree(new File("Tom.json"));// 遍历Iterator<JsonNode> elements = treeNode.elements();while (elements.hasNext()) {System.out.println(elements.next());}}

输出结果：

树到Java对象转换

通过mapper.treeToValue + Class对象，转换成指定POJO。

    @Testpublic void testTree2JavaObj() throws JsonGenerationException, JsonMappingException, IOException {ObjectNode rootNode = mapper.createObjectNode();ArrayNode marksNode = mapper.createArrayNode();marksNode.add(100);marksNode.add(95);marksNode.add(85);rootNode.put("name", "Tom");rootNode.put("age", 21);rootNode.put("verified", false);rootNode.set("marks", marksNode);mapper.writeValue(new File("Tom.json"), rootNode);JsonNode treeNode = mapper.readTree(new File("Tom.json"));Student stuTom = mapper.treeToValue(treeNode, Student.class);System.out.println(stuTom);}/*** 学生类* <br>类名：Student<br>*/static class Student {String name;int age;boolean verified;int[] marks;// getter-setter@Overridepublic String toString() {return "Student [name=" + name + ", age=" + age + ", verified=" + verified + ", marks="+ Arrays.toString(marks) + "]";}}

输出结果：