Gson fromJson() 用法
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1.纯数组JSON 字符串转换 |
[ {"name": "zhangsan","age": "10","phone": "11111","email": "11111@11.com"}, {"name": "lisi","age": "20","phone": "22222","email": "22222@22.com"}, ...] 解析代码如下： public class UserBean { //变量名跟JSON数据字段名必须一致 private String name ; private String age; private String phone; private String email; ... }
//拿到本地JSON 并转成String String strByJson = ConstructTestJsonStr();//此处函数内容省略
//Json的解析类对象 JsonParser parser = new JsonParser(); //将JSON的String 转成一个JsonArray对象 JsonArray jsonArray = parser.parse(strByJson).getAsJsonArray();
Gson gson = new Gson(); ArrayList<UserBean> userBeanList = new ArrayList<>();
//加强for循环遍历JsonArray for (JsonElement user : jsonArray) { //使用GSON，直接转成Bean对象 UserBean userBean = gson.fromJson(user, UserBean.class); userBeanList.add(userBean); } |
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2.有数据头的纯数组 数据转换 |
{"name": "lisi","age": "20","phone": "22222","email": "22222@22.com"}, //解析有数据头的纯数组 //拿到本地JSON 并转成String String strByJson = ConstructTestJsonStr();//此处函数内容省略；
//先转JsonObject JsonObject jsonObject = new JsonParser().parse(strByJson).getAsJsonObject(); //再转JsonArray 加上数据头 JsonArray jsonArray = jsonObject.getAsJsonArray("muser");
Gson gson = new Gson(); ArrayList<UserBean> userBeanList = new ArrayList<>();
//循环遍历 for (JsonElement user : jsonArray) { //通过反射 得到UserBean.class UserBean userBean = gson.fromJson(user, new TypeToken<UserBean>() {}.getType()); userBeanList.add(userBean); } |
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3.有数据头的复杂 数据转换 |
"muser": [{"name": "zhangsan","age": "10","phone": "11111","email":"11111@11.com"},
{"name": "lisi","age": "20","phone": "22222","email": "22222@22.com"},
...]
}
被解析对象不是纯数组数据，还有其它字段+数组（含头），方法如下： 根据 JSON 建立Bean，注意这里的 Bean 是返回所有字段，因为 GSON 能直接解析成 List ，所以 Bean 是下面这样的，同样把占地方的get/set省略： public class ResultBean {
//注意变量名与字段名必须一致
private int code; private String msg; private List<UserBean> muser; public class UserBean{
private String name ; private String age; private String phone; private String email; ... } ... } //有消息头 复杂数据 常规方式 方法如下 //拿到Json字符串 String strByJson = ConstructTestJsonStr();//此处函数内容省略； //GSON直接解析成对象 ResultBean resultBean = new Gson().fromJson(strByJson,ResultBean.class); //对象中拿到集合 List<ResultBean.UserBean> userBeanList = resultBean.getMuser(); 三句话搞定，由此看出GSON的强大 |
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4.只解析复杂JSON中的 数组或数组中的某部分内容 |
有数据头 复杂数据 截取方式，如对第3例中JSON数据内容只想取“muser”数组中年龄（age）大于30岁的怎么办？ 方法1：全部解析，再从 List 中取。（但假如有1万条数据？全部解析太麻烦），方法2：条件遍历！（以下代码示例）： //解析代码：
//拿到JSON字符串 String strByJson = ConstructTestJsonStr();//此处函数内容省略； List<UserBean> userBeanList = new ArrayList<>();
//拿到数组 JsonObject jsonObject = new JsonParser().parse(strByJson).getAsJsonObject(); JsonArray jsonArray = jsonObject.getAsJsonArray("muser");
//循环遍历数组 for (JsonElement user : jsonArray) { UserBean userBean = new Gson().fromJson(user, new TypeToken<UserBean>() { }.getType()); //根据条件过滤 if (Integer.parseInt(userBean.getAge()) > 30) { userBeanList.add(userBean); } } |
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5.嵌套超复杂JSON 数据转换 |
三种方式：1，全部解析出来；2，要什么解析什么；3，JsonReader，第1/2招前述已解释，下面示例JsonReader（类似逐节点解释XML） //通过JsonReader的方式去解析 private void parseComplexJArrayByReader() throws IOException { String strByJson = JsonToStringUtil.getStringByJson(this, R.raw.juser_4); JsonReader reader = new JsonReader(new StringReader(strByJson)); try { reader.beginObject(); String tagName = reader.nextName(); if (tagName.equals("group")) { //读group这个节点 readGroup(reader); } reader.endObject(); } finally { reader.close(); } }
//读group这个节点 private void readGroup(JsonReader reader) throws IOException { reader.beginObject(); while (reader.hasNext()) { String tagName = reader.nextName(); if (tagName.equals("user")) { readUser(reader); } else if (tagName.equals("info")) { readInfo(reader); } } reader.endObject(); }
//读用户基本消息 user节点 private void readUser(JsonReader reader) throws IOException { reader.beginObject(); while (reader.hasNext()) { String tag = reader.nextName(); if (tag.equals("name")) { String name = reader.nextString(); nameText.setText(name); } else if (tag.equals("age")) { String age = reader.nextString(); ageText.setText(age); } ... else { reader.skipValue();//忽略 } } reader.endObject(); }
//读用户其他消息 info节点 private void readInfo(JsonReader reader) throws IOException { reader.beginObject(); while (reader.hasNext()) { String tag = reader.nextName(); if (tag.equals("address")) { String address = reader.nextString(); addressText.setText(address); } else if (tag.equals("work")) { String work = reader.nextString(); workText.setText(work); } ... else { reader.skipValue();//忽略 } } reader.endObject(); } |
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6.简单数据+LIST+MAP 转换 |
public class Student { public int id; public String nickName; public int age; public ArrayList<String> books; public HashMap<String, String> booksMap; } Student student = new Student(); student.id = 1; student.nickName = "Jack"; student.age = 22; student.email = "tr@qq.com"; ArrayList<String> books = new ArrayList<String>(); books.add("数学"); books.add("语文"); books.add("英语"); books.add("物理"); books.add("化学"); books.add("生物"); student.books = books; HashMap<String, String> booksMap = new HashMap<String, String>(); booksMap.put("1", "数学"); booksMap.put("2", "语文"); booksMap.put("3", "英语"); booksMap.put("4", "物理"); booksMap.put("5", "化学"); booksMap.put("6", "生物"); student.booksMap = booksMap;
Gson gson = new Gson(); String result = gson.toJson(student); Student studentG = gson.fromJson(result, Student.class);
Log.e("MainActivity", "id:" + studentG.id); Log.e("MainActivity", "nickName:" + studentG.nickName); Log.e("MainActivity", "age:" + studentG.age); Log.e("MainActivity", "email:" + studentG.email); Log.e("MainActivity", "books size:" + studentG.books.size()); Log.e("MainActivity", "booksMap size:" + studentG.booksMap.size());
打印输出 id:1 nickName: Jack age:22 email:tr@qq.com books size:6 booksMap size:6 |
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7.把List或者Map等集合 的泛型换成自定义个class |
泛型定义 public HashMap<String,Book> booksMap; public class Book{ public int id; public String name; } HashMap<String, Book> booksMap = gson.fromJson(result, new TypeToken<HashMap<String, Book>>() { }.getType());
Gson gson = new Gson(); HashMap<String, Book> booksMap = new HashMap<>(); booksMap.put("book1", new Book(1, "Java基础开发")); booksMap.put("book2", new Book(2, "Java设计模式")); booksMap.put("book3", new Book(3, "Java算法")); String dataStr = gson.toJson(booksMap); System.out.println("dataStr:" + dataStr); HashMap<String, Book> booksMap2 = gson.fromJson(dataStr, new TypeToken<HashMap<String, Book>>() { }.getType()); for (Map.Entry<String, Book> entry : booksMap2.entrySet()) { System.out.println("key:"+entry.getKey() + " value:" + entry.getValue().toString()); } 输出结果 dataStr:{"book2":{"id":2,"name":"Java设计模式"},"book1":{"id":1,"name":"Java基础开发"},"book3":{"id":3,"name":"Java算法"}} key:book2 value:Book{id=2, name='Java设计模式'} key:book1 value:Book{id=1, name='Java基础开发'} key:book3 value:Book{id=3, name='Java算法'} |
