从json字符串中获取指定值
目录
一、 FastJSON
1）解析 JSON 字符串为 Java 对象
2）处理嵌套的 JSON 结构（创建java对象）
3）处理嵌套的 JSON 结构（直接从 JSON 对象中获取值）
4）处理嵌套的 JSON 结构（使用路径表达式）
二、Jackson
1）创建java对象
2）直接从 JSON 对象中获取值
三、Gson
1）解析为 Java 对象
2）直接从 JSON 对象中获取值
四、org.json
1）解析为JSONObject对象
2）使用递归遍历 JSON 对象
一、 FastJSON
1）解析 JSON 字符串为 Java 对象
存在一个json字符串：{"name":"John","age":30,"isStudent":false}
//定义一个 Java 类来对应这个 JSON 结构
class Person {private String name;private int age;private boolean isStudent;// 生成相应的 getter 和 setter 方法
}直接从 JSON 对象中获取值
import com.alibaba.fastjson.JSONObject;public class Main {public static void main(String[] args) {String jsonStr = "{\"name\":\"John\",\"age\":30,\"isStudent\":false}";JSONObject jsonObject = JSON.parseObject(jsonStr);String name = jsonObject.getString("name");int age = jsonObject.getInteger("age");boolean isStudent = jsonObject.getBooleanValue("isStudent");System.out.println("Name: " + name);System.out.println("Age: " + age);System.out.println("Is Student: " + isStudent);}
}2）处理嵌套的 JSON 结构（创建java对象）
已知存在一个josn：{"person":{"name":"John","age":30},"address":{"city":"New York","country":"USA"}}
//定义对应的 Java 类
class Person {private String name;private int age;// getter 和 setter 方法
}class Address {private String city;private String country;// getter 和 setter 方法
}class RootObject {private Person person;private Address address;// getter 和 setter 方法
}解析：
import com.alibaba.fastjson.JSON;public class Main {public static void main(String[] args) {String jsonStr = "{\"person\":{\"name\":\"John\",\"age\":30},\"address\":{\"city\":\"New York\",\"country\":\"USA\"}}";RootObject rootObject = JSON.parseObject(jsonStr, RootObject.class);Person person = rootObject.getPerson();Address address = rootObject.getAddress();String name = person.getName();int age = person.getAge();String city = address.getCity();String country = address.getCountry();System.out.println("Name: " + name);System.out.println("Age: " + age);System.out.println("City: " + city);System.out.println("Country: " + country);}
}3）处理嵌套的 JSON 结构（直接从 JSON 对象中获取值）
存在json串：
{"user":{"name":"Alice","age":25,"address":{"city":"New York","country":"USA"}},"orders":[{"id":1,"product":"Book"},{"id":2,"product":"Pen"}]}
import com.alibaba.fastjson.JSONObject;public class Main {public static void main(String[] args) {String jsonStr = "{\"user\":{\"name\":\"Alice\",\"age\":25,\"address\":{\"city\":\"New York\",\"country\":\"USA\"}},\"orders\":[{\"id\":1,\"product\":\"Book\"},{\"id\":2,\"product\":\"Pen\"}]}";JSONObject jsonObject = JSON.parseObject(jsonStr);JSONObject userObject = jsonObject.getJSONObject("user");String userName = userObject.getString("name");int userAge = userObject.getInteger("age");JSONObject addressObject = userObject.getJSONObject("address");String city = addressObject.getString("city");String country = addressObject.getString("country");JSONArray ordersArray = jsonObject.getJSONArray("orders");for (int i = 0; i < ordersArray.size(); i++) {JSONObject orderObject = ordersArray.getJSONObject(i);int orderId = orderObject.getInteger("id");String product = orderObject.getString("product");System.out.println("Order ID: " + orderId + ", Product: " + product);}System.out.println("User Name: " + userName);System.out.println("User Age: " + userAge);System.out.println("City: " + city);System.out.println("Country: " + country);}
}4）处理嵌套的 JSON 结构（使用路径表达式）
存在json串：
{"user":{"name":"Alice","age":25,"address":{"city":"New York","country":"USA"}},"orders":[{"id":1,"product":"Book"},{"id":2,"product":"Pen"}]}
import com.alibaba.fastjson.JSONPath;public class Main {public static void main(String[] args) {String jsonStr = "{\"user\":{\"name\":\"Alice\",\"age\":25,\"address\":{\"city\":\"New York\",\"country\":\"USA\"}},\"orders\":[{\"id\":1,\"product\":\"Book\"},{\"id\":2,\"product\":\"Pen\"}]}";String userName = (String) JSONPath.read(jsonStr, "$.user.name");int userAge = (int) JSONPath.read(jsonStr, "$.user.age");String city = (String) JSONPath.read(jsonStr, "$.user.address.city");String country = (String) JSONPath.read(jsonStr, "$.user.address.country");Object[] orders = JSONPath.read(jsonStr, "$.orders");for (Object order : orders) {int orderId = (int) JSONPath.read(order, "$.id");String product = (String) JSONPath.read(order, "$.product");System.out.println("Order ID: " + orderId + ", Product: " + product);}System.out.println("User Name: " + userName);System.out.println("User Age: " + userAge);System.out.println("City: " + city);System.out.println("Country: " + country);}
}二、Jackson
1）创建java对象
已知存在json串：
{"person":{"name":"Alice","age":25,"address":{"city":"New York","country":"USA"}},"orders":[{"id":1,"product":"Book"},{"id":2,"product":"Pen"}]}
class Address {private String city;private String country;// Getters and setters
}class Order {private int id;private String product;// Getters and setters
}class Person {private String name;private int age;private Address address;// Getters and setters
}class RootObject {private Person person;private Order[] orders;// Getters and setters
}使用 Jackson 进行解析到对象中
import com.fasterxml.jackson.databind.ObjectMapper;public class Main {public static void main(String[] args) throws Exception {String jsonStr = "{\"person\":{\"name\":\"Alice\",\"age\":25,\"address\":{\"city\":\"New York\",\"country\":\"USA\"}},\"orders\":[{\"id\":1,\"product\":\"Book\"},{\"id\":2,\"product\":\"Pen\"}]}";ObjectMapper objectMapper = new ObjectMapper();RootObject rootObject = objectMapper.readValue(jsonStr, RootObject.class);String name = rootObject.getPerson().getName();int age = rootObject.getPerson().getAge();String city = rootObject.getPerson().getAddress().getCity();String country = rootObject.getPerson().getAddress().getCountry();Order[] orders = rootObject.getOrders();for (Order order : orders) {int orderId = order.getId();String product = order.getProduct();System.out.println("Order ID: " + orderId + ", Product: " + product);}System.out.println("Name: " + name);System.out.println("Age: " + age);System.out.println("City: " + city);System.out.println("Country: " + country);}
}2）直接从 JSON 对象中获取值
已知存在json串：
{"person":{"name":"Alice","age":25,"address":{"city":"New York","country":"USA"}},"orders":[{"id":1,"product":"Book"},{"id":2,"product":"Pen"}]}
import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;public class Main {public static void main(String[] args) throws Exception {String jsonStr = "{\"person\":{\"name\":\"Alice\",\"age\":25,\"address\":{\"city\":\"New York\",\"country\":\"USA\"}},\"orders\":[{\"id\":1,\"product\":\"Book\"},{\"id\":2,\"product\":\"Pen\"}]}";ObjectMapper objectMapper = new ObjectMapper();JsonNode rootNode = objectMapper.readTree(jsonStr);JsonNode personNode = rootNode.get("person");String name = personNode.get("name").asText();int age = personNode.get("age").asInt();JsonNode addressNode = personNode.get("address");String city = addressNode.get("city").asText();String country = addressNode.get("country").asText();JsonNode ordersNode = rootNode.get("orders");for (JsonNode orderNode : ordersNode) {int orderId = orderNode.get("id").asInt();String product = orderNode.get("product").asText();System.out.println("Order ID: " + orderId + ", Product: " + product);}System.out.println("Name: " + name);System.out.println("Age: " + age);System.out.println("City: " + city);System.out.println("Country: " + country);}
}三、Gson
1）解析为 Java 对象
已知存在json串：{"person":{"name":"Alice","age":25,"address":{"city":"New York","country":"USA"}},"orders":[{"id":1,"product":"Book"},{"id":2,"product":"Pen"}]}
定义对应的 Java 类：
class Address {private String city;private String country;// Getters and setters
}class Order {private int id;private String product;// Getters and setters
}class Person {private String name;private int age;private Address address;// Getters and setters
}class RootObject {private Person person;private Order[] orders;// Getters and setters
}使用 Gson 进行解析：
import com.google.gson.Gson;public class Main {public static void main(String[] args) {String jsonStr = "{\"person\":{\"name\":\"Alice\",\"age\":25,\"address\":{\"city\":\"New York\",\"country\":\"USA\"}},\"orders\":[{\"id\":1,\"product\":\"Book\"},{\"id\":2,\"product\":\"Pen\"}]}";Gson gson = new Gson();RootObject rootObject = gson.fromJson(jsonStr, RootObject.class);String name = rootObject.getPerson().getName();int age = rootObject.getPerson().getAge();String city = rootObject.getPerson().getAddress().getCity();String country = rootObject.getPerson().getAddress().getCountry();Order[] orders = rootObject.getOrders();for (Order order : orders) {int orderId = order.getId();String product = order.getProduct();System.out.println("Order ID: " + orderId + ", Product: " + product);}System.out.println("Name: " + name);System.out.println("Age: " + age);System.out.println("City: " + city);System.out.println("Country: " + country);}
}2）直接从 JSON 对象中获取值
已知存在json串：{"person":{"name":"Alice","age":25,"address":{"city":"New York","country":"USA"}},"orders":[{"id":1,"product":"Book"},{"id":2,"product":"Pen"}]}
不创建 Java 对象，直接从 JSON 对象获取值：
import com.google.gson.JsonObject;
import com.google.gson.JsonParser;public class Main {public static void main(String[] args) {String jsonStr = "{\"person\":{\"name\":\"Alice\",\"age\":25,\"address\":{\"city\":\"New York\",\"country\":\"USA\"}},\"orders\":[{\"id\":1,\"product\":\"Book\"},{\"id\":2,\"product\":\"Pen\"}]}";JsonObject jsonObject = JsonParser.parseString(jsonStr).getAsJsonObject();JsonObject personObject = jsonObject.getAsJsonObject("person");String name = personObject.get("name").getAsString();int age = personObject.get("age").getAsInt();JsonObject addressObject = personObject.getAsJsonObject("address");String city = addressObject.get("city").getAsString();String country = addressObject.get("country").getAsString();JsonArray ordersArray = jsonObject.getAsJsonArray("orders");for (JsonElement orderElement : ordersArray) {JsonObject orderObject = orderElement.getAsJsonObject();int orderId = orderObject.get("id").getAsInt();String product = orderObject.get("product").getAsString();System.out.println("Order ID: " + orderId + ", Product: " + product);}System.out.println("Name: " + name);System.out.println("Age: " + age);System.out.println("City: " + city);System.out.println("Country: " + country);}
}四、org.json
1）解析为JSONObject对象
已知存在json串：{"person":{"name":"Alice","age":25,"address":{"city":"New York","country":"USA"}},"orders":[{"id":1,"product":"Book"},{"id":2,"product":"Pen"}]}
使用org.json解析：
import org.json.JSONArray;
import org.json.JSONObject;public class Main {public static void main(String[] args) {String jsonStr = "{\"person\":{\"name\":\"Alice\",\"age\":25,\"address\":{\"city\":\"New York\",\"country\":\"USA\"}},\"orders\":[{\"id\":1,\"product\":\"Book\"},{\"id\":2,\"product\":\"Pen\"}]}";JSONObject jsonObject = new JSONObject(jsonStr);// 获取 person 对象JSONObject personObject = jsonObject.getJSONObject("person");String name = personObject.getString("name");int age = personObject.getInt("age");// 获取 address 对象JSONObject addressObject = personObject.getJSONObject("address");String city = addressObject.getString("city");String country = addressObject.getString("country");// 获取 orders 数组JSONArray ordersArray = jsonObject.getJSONArray("orders");for (int i = 0; i < ordersArray.length(); i++) {JSONObject orderObject = ordersArray.getJSONObject(i);int orderId = orderObject.getInt("id");String product = orderObject.getString("product");System.out.println("Order ID: " + orderId + ", Product: " + product);}System.out.println("Name: " + name);System.out.println("Age: " + age);System.out.println("City: " + city);System.out.println("Country: " + country);}
}2）使用递归遍历 JSON 对象
已知存在json串：已知存在json串：{"person":{"name":"Alice","age":25,"address":{"city":"New York","country":"USA"}},"orders":[{"id":1,"product":"Book"},{"id":2,"product":"Pen"}]}
如果 JSON 结构更加复杂，可以使用递归的方式遍历获取值。
import org.json.JSONArray;
import org.json.JSONObject;public class Main {public static void traverseJSON(JSONObject jsonObject) {for (String key : JSONObject.getNames(jsonObject)) {Object value = jsonObject.get(key);if (value instanceof JSONObject) {traverseJSON((JSONObject) value);} else if (value instanceof JSONArray) {JSONArray array = (JSONArray) value;for (int i = 0; i < array.length(); i++) {Object item = array.get(i);if (item instanceof JSONObject) {traverseJSON((JSONObject) item);} else {// 处理基本类型的值System.out.println(key + ": " + item);}}} else {// 处理基本类型的值System.out.println(key + ": " + value);}}}public static void main(String[] args) {String jsonStr = "{\"person\":{\"name\":\"Alice\",\"age\":25,\"address\":{\"city\":\"New York\",\"country\":\"USA\"}},\"orders\":[{\"id\":1,\"product\":\"Book\"},{\"id\":2,\"product\":\"Pen\"}]}";JSONObject jsonObject = new JSONObject(jsonStr);traverseJSON(jsonObject);}
}