GSON入门篇（教学视频+源代码）

package com.bjpowernode.test; import com.bjpowernode.domain.User; import com.google.gson.Gson; import com.google.gson.reflect.TypeToken; import com.sun.deploy.security.ValidationState; import org.junit.Test; import java.lang.reflect.Type; import java.util.ArrayList; import java.util.List; public class TestGSONAPI { /** * 测试一个对象转JSON */ @Test public void testOneObjectConvertToJSON(){ User user = new User(1,"zhangsan","123456","三丰大师",149) ; Gson gson = new Gson(); //写法一 System.out.println("=======================写法一========================="); String userJson = gson.toJson(user, User.class); System.out.println("userJson = " + userJson);//userJson = {"id":1,"username":"zhangsan","password":"123456","nickname":"三丰大师","age":149} //写法二 System.out.println("========================写法二========================="); String userJson2 = gson.toJson(user); System.out.println("userJson2 = " + userJson2); } /** * 测试多个对象转JSON */ @Test public void testManyObjectConvertToJSON(){ List<User> users = new ArrayList<>(); User user = null; for (int i = 1; i <=5 ; i++) { user = new User(i,"hhh"+i,123456+"i","哈哈哈"+i,24+i); users.add(user); } Gson gson = new Gson(); String usersJson = gson.toJson(users); System.out.println("usersJson = " + usersJson); } /** * 测试JSON字符串转一个对象 */ @Test public void testJSONSConvertToOneObject(){ //如何将JSON字符串转换成对象 String jsonStr = "{\"id\":1,\"username\":\"zhangsan\",\"password\":\"123456\",\"nickname\":\"三丰大师\",\"age\":149}"; Gson gson = new Gson(); User user = gson.fromJson(jsonStr, User.class); System.out.println("user = " + user); } /** * 测试JSON字符串转多个对象（List）（错误案例） */ @Test public void testJSONConvertManyObjectErrorInstance(){ String jsonStr = "[{\"id\":1,\"username\":\"hhh1\",\"password\":\"123456i\",\"nickname\":\"哈哈哈1\",\"age\":25},{\"id\":2,\"username\":\"hhh2\",\"password\":\"123456i\",\"nickname\":\"哈哈哈2\",\"age\":26},{\"id\":3,\"username\":\"hhh3\",\"password\":\"123456i\",\"nickname\":\"哈哈哈3\",\"age\":27},{\"id\":4,\"username\":\"hhh4\",\"password\":\"123456i\",\"nickname\":\"哈哈哈4\",\"age\":28},{\"id\":5,\"username\":\"hhh5\",\"password\":\"123456i\",\"nickname\":\"哈哈哈5\",\"age\":29}]\n"; Gson gson = new Gson(); ArrayList<User> arrayList = gson.fromJson(jsonStr, ArrayList.class); /*上面这行代码，使得结果输出如下： * {id=1.0, username=hhh1, password=123456i, nickname=哈哈哈1, age=25.0} {id=2.0, username=hhh2, password=123456i, nickname=哈哈哈2, age=26.0} {id=3.0, username=hhh3, password=123456i, nickname=哈哈哈3, age=27.0} {id=4.0, username=hhh4, password=123456i, nickname=哈哈哈4, age=28.0} {id=5.0, username=hhh5, password=123456i, nickname=哈哈哈5, age=29.0} 输出的结果，既不是对象，也不是JSON字符串 对象 ：User(id=1, username=zhangsan, password=123456, nickname=三丰大师, age=149) JSON字符串 : {"id":1,"username":"zhangsan","password":"123456","nickname":"三丰大师","age":149} */ // for (Object o : arrayList) { // System.out.println(o); // } arrayList.forEach(System.out::println); } /** * 测试JSON字符串转多个对象（List）（正确案例） * 引入TypeToken */ @Test public void testJSONConvertManyObjectCorrectInstance(){ String jsonStr = "[{\"id\":1,\"username\":\"hhh1\",\"password\":\"123456i\",\"nickname\":\"哈哈哈1\",\"age\":25},{\"id\":2,\"username\":\"hhh2\",\"password\":\"123456i\",\"nickname\":\"哈哈哈2\",\"age\":26},{\"id\":3,\"username\":\"hhh3\",\"password\":\"123456i\",\"nickname\":\"哈哈哈3\",\"age\":27},{\"id\":4,\"username\":\"hhh4\",\"password\":\"123456i\",\"nickname\":\"哈哈哈4\",\"age\":28},{\"id\":5,\"username\":\"hhh5\",\"password\":\"123456i\",\"nickname\":\"哈哈哈5\",\"age\":29}]\n"; Gson gson = new Gson(); Type type = new TypeToken<ArrayList<User>>(){}.getType(); ArrayList<User> arrayList = gson.fromJson(jsonStr, type); // for (User user : arrayList) { // System.out.println(user); // } arrayList.forEach(System.out::println); /* 输出结果如下 * User(id=1, username=hhh1, password=123456i, nickname=哈哈哈1, age=25) User(id=2, username=hhh2, password=123456i, nickname=哈哈哈2, age=26) User(id=3, username=hhh3, password=123456i, nickname=哈哈哈3, age=27) User(id=4, username=hhh4, password=123456i, nickname=哈哈哈4, age=28) User(id=5, username=hhh5, password=123456i, nickname=哈哈哈5, age=29) * */ } }