Java中GSON的使用（内含源代码）

Java中GSON的使用（内含源代码）

源代码下载链接地址：https://download.csdn.net/download/weixin_46411355/87474951

1.1 GSON简介

JSON(JavaScript Object Notation)是一种轻量级的数据交换格式。易于人阅读和编写。同时也易于机器解析和生成。
Gson是Google提供的用来在Java对象和JSON数据之间进行映射的Java类库。可以将一个JSON字符串转成一个Java对象(反序列化)，或者反过来(序列化)。

GSON地址：google/gson (github.com)

Android引入GSON：

implementation ‘com.google.code.gson:gson:2.9.0’

1.2 JavaBean序列化/反序列化

1.2.1 步骤说明

0. 导入Gson的jar包
1. 创建JavaBean为User（String username,String password,int age,boolean
   isStudent）
2. 实例化JavaBean对象user1
3. 创建GSON对象gson
4. 利用gson对象进行JavaBean的序列化
5. 利用gson对象进行JavaBean的反序列化

下载gson的jar包，这里笔者提供笔者的gson jar包的下载链接地址：https://download.csdn.net/download/weixin_46411355/87474404

创建一个JavaSe项目，在项目中创建一个lib目录，将这个jar包放进lib目录
鼠标右键jar包，点击Add as Library 即可

普通JavaBean

JavaBean
User.java对象

package _1JavaBean序列化和反序列化._01普通JavaBean;import com.sun.jmx.snmp.mpm.SnmpMsgTranslator;import java.io.Serializable;
import java.util.Objects;public class User implements Serializable {private String username;private String password;private int age;boolean isStudent;public User() {}public User(String username, String password, int age, boolean isStudent) {this.username = username;this.password = password;this.age = age;this.isStudent = isStudent;}public String getUsername() {return username;}public void setUsername(String username) {this.username = username;}public String getPassword() {return password;}public void setPassword(String password) {this.password = password;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}public boolean isStudent() {return isStudent;}public void setStudent(boolean student) {isStudent = student;}@Overridepublic String toString() {return "User{" +"username='" + username + '\'' +", password='" + password + '\'' +", age=" + age +", isStudent=" + isStudent +'}';}@Overridepublic boolean equals(Object o) {if (this == o) return true;if (o == null || getClass() != o.getClass()) return false;User user = (User) o;return age == user.age &&isStudent == user.isStudent &&Objects.equals(username, user.username) &&Objects.equals(password, user.password);}@Overridepublic int hashCode() {return Objects.hash(username, password, age, isStudent);}
}

测试类

package _1JavaBean序列化和反序列化._01普通JavaBean;import com.google.gson.Gson;public class TestJavaBean {public static void main(String[] args) {User user1 = new User("zhangsan", "123", 18, false);Gson gson = new Gson();//创建Gson对象String userJson = gson.toJson(user1);//序列化System.out.println("序列化：" + userJson);User user2 = gson.fromJson(userJson, User.class);//反序列化System.out.println("反序列化：" + user2);}}

测试效果

嵌套JavaBean

在普通JavaBean的基础上创建Job（String name,BigDecimal salary），并在User对象中添加Job属性

Job.java

package _1JavaBean序列化和反序列化._02嵌套JavaBean;import java.io.Serializable;
import java.math.BigDecimal;
import java.util.Objects;public class Job implements Serializable {private String name;private BigDecimal salary;public Job() {}public Job(String name, BigDecimal salary) {this.name = name;this.salary = salary;}public String getName() {return name;}public void setName(String name) {this.name = name;}public BigDecimal getSalary() {return salary;}public void setSalary(BigDecimal salary) {this.salary = salary;}@Overridepublic String toString() {return "Job{" +"name='" + name + '\'' +", salary=" + salary +'}';}@Overridepublic boolean equals(Object o) {if (this == o) return true;if (o == null || getClass() != o.getClass()) return false;Job job = (Job) o;return Objects.equals(name, job.name) &&Objects.equals(salary, job.salary);}@Overridepublic int hashCode() {return Objects.hash(name, salary);}
}

User.java

package _1JavaBean序列化和反序列化._02嵌套JavaBean;import java.io.Serializable;
import java.util.Objects;public class User implements Serializable {private String username;private String password;private int age;boolean isStudent;private Job job;public Job getJob() {return job;}public void setJob(Job job) {this.job = job;}public User(String username, String password, int age, boolean isStudent, Job job) {this.username = username;this.password = password;this.age = age;this.isStudent = isStudent;this.job = job;}public User() {}public User(String username, String password, int age, boolean isStudent) {this.username = username;this.password = password;this.age = age;this.isStudent = isStudent;}public String getUsername() {return username;}public void setUsername(String username) {this.username = username;}public String getPassword() {return password;}public void setPassword(String password) {this.password = password;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}public boolean isStudent() {return isStudent;}public void setStudent(boolean student) {isStudent = student;}@Overridepublic String toString() {return "User{" +"username='" + username + '\'' +", password='" + password + '\'' +", age=" + age +", isStudent=" + isStudent +'}';}@Overridepublic boolean equals(Object o) {if (this == o) return true;if (o == null || getClass() != o.getClass()) return false;User user = (User) o;return age == user.age &&isStudent == user.isStudent &&Objects.equals(username, user.username) &&Objects.equals(password, user.password);}@Overridepublic int hashCode() {return Objects.hash(username, password, age, isStudent);}
}

测试类

package _1JavaBean序列化和反序列化._02嵌套JavaBean;import com.google.gson.Gson;import java.math.BigDecimal;public class TestNestedJavaBean {public static void main(String[] args) {User user1 = new User("zhangsan","123",18,false);Gson gson = new Gson();//创建Gson对象Job job = new Job("自有职业",new BigDecimal(2500.00));user1.setJob(job);String user1Json = gson.toJson(user1);//序列化System.out.println("序列化："+user1Json);User user2 = gson.fromJson(user1Json, User.class);System.out.println("反序列化："+user2);}
}

测试效果

1.3 数组和List的序列化/反序列化

1.3.1 数组的序列化/反序列化

数组类型对象和普通对象一样，使用toJson/fromJson即可完成序列化与反序列化。

JavaBean
User.java

package _2数组和List的序列化和反序列化._01数组的序列化和反序列化;import java.io.Serializable;
import java.util.Objects;public class User implements Serializable {private String username;private String password;private int age;boolean isStudent;public User() {}public User(String username, String password, int age, boolean isStudent) {this.username = username;this.password = password;this.age = age;this.isStudent = isStudent;}public String getUsername() {return username;}public void setUsername(String username) {this.username = username;}public String getPassword() {return password;}public void setPassword(String password) {this.password = password;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}public boolean isStudent() {return isStudent;}public void setStudent(boolean student) {isStudent = student;}@Overridepublic String toString() {return "User{" +"username='" + username + '\'' +", password='" + password + '\'' +", age=" + age +", isStudent=" + isStudent +'}';}@Overridepublic boolean equals(Object o) {if (this == o) return true;if (o == null || getClass() != o.getClass()) return false;User user = (User) o;return age == user.age &&isStudent == user.isStudent &&Objects.equals(username, user.username) &&Objects.equals(password, user.password);}@Overridepublic int hashCode() {return Objects.hash(username, password, age, isStudent);}
}

测试类

package _2数组和List的序列化和反序列化._01数组的序列化和反序列化;import com.google.gson.Gson;public class TestArray {public static void main(String[] args) {User[] users1 = new User[3];users1[0] = new User("zhangsan","123",18,false);users1[1] = new User("lisi","333",20,true);Gson gson = new Gson();//创建GSON对象String users1Json = gson.toJson(users1);//序列化System.out.println("序列化："+users1Json);User[] users2 = gson.fromJson(users1Json,User[].class);//反序列化System.out.println("反序列化0："+users2[0].getUsername());System.out.println("反序列化1："+users2[1]);System.out.println("反序列化2："+users2[2]);}
}

测试效果

1.3.2 List集合的序列化/反序列化

List集合类型对象需要注意的是，在反序列化时因为Java是伪泛型，泛型擦除会导致无法反序列化为List，需要使用TypeToken完成反序列化。

javabean
User.java

package _2数组和List的序列化和反序列化._02List集合的序列化和反序列化;import java.io.Serializable;
import java.util.Objects;public class User implements Serializable {private String username;private String password;private int age;boolean isStudent;public User() {}public User(String username, String password, int age, boolean isStudent) {this.username = username;this.password = password;this.age = age;this.isStudent = isStudent;}public String getUsername() {return username;}public void setUsername(String username) {this.username = username;}public String getPassword() {return password;}public void setPassword(String password) {this.password = password;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}public boolean isStudent() {return isStudent;}public void setStudent(boolean student) {isStudent = student;}@Overridepublic String toString() {return "User{" +"username='" + username + '\'' +", password='" + password + '\'' +", age=" + age +", isStudent=" + isStudent +'}';}@Overridepublic boolean equals(Object o) {if (this == o) return true;if (o == null || getClass() != o.getClass()) return false;User user = (User) o;return age == user.age &&isStudent == user.isStudent &&Objects.equals(username, user.username) &&Objects.equals(password, user.password);}@Overridepublic int hashCode() {return Objects.hash(username, password, age, isStudent);}
}

测试类

package _2数组和List的序列化和反序列化._02List集合的序列化和反序列化;import com.google.gson.Gson;
import com.google.gson.reflect.TypeToken;import java.lang.reflect.Type;
import java.util.ArrayList;
import java.util.List;public class TestList {public static void main(String[] args) {List<User> userList1 = new ArrayList<>();userList1.add(new User("zhangsan", "123", 18, false));userList1.add(new User("lisi", "333", 20, true));Gson gson = new Gson();//创建Gson对象String userList1Json = gson.toJson(userList1);//序列化System.out.println("序列化：" + userList1Json);Type type = new TypeToken<List<User>>() {}.getType();//泛型类型，import com.google.gson.reflect.TypeToken;List<User> userList2 = gson.fromJson(userList1Json, type);//反序列化System.out.println("反序列化0："+userList2.get(0).getUsername());System.out.println("反序列化1："+userList2.get(1));}
}

测试结果

1.4 Set和Map的序列化/反序列化

Set集合类型和Map集合类型对象在反序列化时与List一样，需要使用TypeToken完成反序列化。

1.4.1 Set集合的序列化/反序列化

javabean
User.java

package _3Set和Map的序列化和反序列化._01Set集合的序列化和反序列化;import java.io.Serializable;
import java.util.Objects;public class User implements Serializable {private String username;private String password;private int age;boolean isStudent;public User() {}public User(String username, String password, int age, boolean isStudent) {this.username = username;this.password = password;this.age = age;this.isStudent = isStudent;}public String getUsername() {return username;}public void setUsername(String username) {this.username = username;}public String getPassword() {return password;}public void setPassword(String password) {this.password = password;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}public boolean isStudent() {return isStudent;}public void setStudent(boolean student) {isStudent = student;}@Overridepublic String toString() {return "User{" +"username='" + username + '\'' +", password='" + password + '\'' +", age=" + age +", isStudent=" + isStudent +'}';}@Overridepublic boolean equals(Object o) {if (this == o) return true;if (o == null || getClass() != o.getClass()) return false;User user = (User) o;return age == user.age &&isStudent == user.isStudent &&Objects.equals(username, user.username) &&Objects.equals(password, user.password);}@Overridepublic int hashCode() {return Objects.hash(username, password, age, isStudent);}
}

测试类

package _3Set和Map的序列化和反序列化._01Set集合的序列化和反序列化;import com.google.gson.Gson;
import com.google.gson.reflect.TypeToken;import java.lang.reflect.Type;
import java.util.HashSet;
import java.util.Set;public class TestSet {public static void main(String[] args) {Set<User> userSet1 = new HashSet<>();userSet1.add(new User("zhangsan","123",18,false));userSet1.add(new User("lisi","333",20,true));userSet1.add(null);Gson gson = new Gson(); //创建GSON对象String userSet1Json = gson.toJson(userSet1);//序列化System.out.println("序列化："+userSet1Json);Type type = new TypeToken<Set<User>>() {}.getType();//泛型类型，import com.google.gson.reflect.TypeToken;Set<User> userSet2 = gson.fromJson(userSet1Json, type);//反序列化for (User user : userSet2) {System.out.println(user);}}
}

测试效果

1.4.2 Map集合的序列化/反序列化

javabean
User.java

package _3Set和Map的序列化和反序列化._02Map集合的序列化和反序列化;import java.io.Serializable;
import java.util.Objects;public class User implements Serializable {private String username;private String password;private int age;boolean isStudent;public User() {}public User(String username, String password, int age, boolean isStudent) {this.username = username;this.password = password;this.age = age;this.isStudent = isStudent;}public String getUsername() {return username;}public void setUsername(String username) {this.username = username;}public String getPassword() {return password;}public void setPassword(String password) {this.password = password;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}public boolean isStudent() {return isStudent;}public void setStudent(boolean student) {isStudent = student;}@Overridepublic String toString() {return "User{" +"username='" + username + '\'' +", password='" + password + '\'' +", age=" + age +", isStudent=" + isStudent +'}';}@Overridepublic boolean equals(Object o) {if (this == o) return true;if (o == null || getClass() != o.getClass()) return false;User user = (User) o;return age == user.age &&isStudent == user.isStudent &&Objects.equals(username, user.username) &&Objects.equals(password, user.password);}@Overridepublic int hashCode() {return Objects.hash(username, password, age, isStudent);}
}

测试类

package _3Set和Map的序列化和反序列化._02Map集合的序列化和反序列化;import com.google.gson.Gson;
import com.google.gson.reflect.TypeToken;import java.lang.reflect.Type;
import java.util.HashMap;
import java.util.Map;public class TestMap {public static void main(String[] args) {Map<String,User> userMap1 = new HashMap<>();userMap1.put("1",new User("zhangsan","123",18,false));userMap1.put("2",new User("lisi","333",20,true));userMap1.put("3",null);userMap1.put(null,null);Gson gson = new Gson();//參加Gson对象String userMap1Json = gson.toJson(userMap1);//序列化System.out.println("序列化："+userMap1Json);Type type = new TypeToken<Map<String, User>>(){}.getType();//泛型类型   import com.google.gson.reflect.TypeToken;Map<String,User> userMap2 = gson.fromJson(userMap1Json, type);//反序列化
//        for (Object user : userMap2.entrySet()) {
//            System.out.println(user);
//        }userMap2.entrySet().forEach(System.out::println);}
}

测试结果

1.5 Map的value为null时的序列化/反序列化

如果一个Map的value为NULL，那么按照GSON默认的处理为忽略这个map项

1.6 控制序列化/反序列化的变量名称

如果希望JSON字符串字段名不以变量名作为Key，比如SON字符串中的Key存在Java中的关键字时，可以借助@SerializedName注解控制JSON字段中Key的命名。

如果希望指定GSON对某些字段配置是否参与序列化与反序列化可以使用@Expose注解控制，同时使用GsonBuilder创建Gson对象:

另外直接使用transient关键字修饰的变量，也可以让该变量不参与序列化/反序列化

之前，我们都是假设 model字段都是需要序列化和反序列化的，这是一种最简单的情况，可真实的情况并不是如此，所以我们需要定制我们的解析规则。从而引出@Expose注解。

@Expose注解
当你不需要完全序列化model字段时，我们就可以使用@Expose来帮我解决。

查看@Expose的源码如下

@Expose默认有两个属性：serialize（是否序列化） 和 deserialize（是否反序列化），默认值都为true。如果你给字段设置了@Expose注解，但是没有设置serialize和deserialize，那model的字段都将会输出。

transient
使用transient来描述字段，将不能被序列化和反序列化

@SerializedName(“XXX”)
使用@SerializedName(“XXX”)注解可以实现以"XXX"作为字段名

1.6.1 JavaBean

job类

package _4控制序列化和反序列化的变量名称;import com.google.gson.annotations.Expose;import java.io.Serializable;
import java.math.BigDecimal;
import java.util.Objects;public class Job implements Serializable {@Exposeprivate String name;@Exposeprivate BigDecimal salary;public Job() {}public Job(String name, BigDecimal salary) {this.name = name;this.salary = salary;}public String getName() {return name;}public void setName(String name) {this.name = name;}public BigDecimal getSalary() {return salary;}public void setSalary(BigDecimal salary) {this.salary = salary;}@Overridepublic String toString() {return "Job{" +"name='" + name + '\'' +", salary=" + salary +'}';}@Overridepublic boolean equals(Object o) {if (this == o) return true;if (o == null || getClass() != o.getClass()) return false;Job job = (Job) o;return Objects.equals(name, job.name) &&Objects.equals(salary, job.salary);}@Overridepublic int hashCode() {return Objects.hash(name, salary);}
}

User类

package _4控制序列化和反序列化的变量名称;import com.google.gson.annotations.Expose;
import com.google.gson.annotations.SerializedName;import java.util.Objects;public class User {@Exposeprivate String username;@Exposeprivate String password;@Exposeprivate int age;@Exposeprivate boolean isStudent;@Exposeprivate Job job;//serialize：是否参与序列化，deserialize是否参与反序列化@Expose(serialize = false,deserialize = false)private int test1;//使用transient来描述字段，将不能被序列化和反序列化private transient int test2;//使用@SerializedName("class")注解可以实现以"class"作为字段名@Expose@SerializedName("class")private int clazz;public User() {}public User(String username, String password, int age, boolean isStudent) {this.username = username;this.password = password;this.age = age;this.isStudent = isStudent;}public User(String username, String password, int age, boolean isStudent, Job job, int test1, int test2, int clazz) {this.username = username;this.password = password;this.age = age;this.isStudent = isStudent;this.job = job;this.test1 = test1;this.test2 = test2;this.clazz = clazz;}public String getUsername() {return username;}public void setUsername(String username) {this.username = username;}public String getPassword() {return password;}public void setPassword(String password) {this.password = password;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}public boolean isStudent() {return isStudent;}public void setStudent(boolean student) {isStudent = student;}public Job getJob() {return job;}public void setJob(Job job) {this.job = job;}public int getTest1() {return test1;}public void setTest1(int test1) {this.test1 = test1;}public int getTest2() {return test2;}public void setTest2(int test2) {this.test2 = test2;}public int getClazz() {return clazz;}public void setClazz(int clazz) {this.clazz = clazz;}@Overridepublic String toString() {return "User{" +"username='" + username + '\'' +", password='" + password + '\'' +", age=" + age +", isStudent=" + isStudent +", job=" + job +", test1=" + test1 +", test2=" + test2 +", clazz=" + clazz +'}';}@Overridepublic boolean equals(Object o) {if (this == o) return true;if (o == null || getClass() != o.getClass()) return false;User user = (User) o;return age == user.age &&isStudent == user.isStudent &&test1 == user.test1 &&test2 == user.test2 &&clazz == user.clazz &&Objects.equals(username, user.username) &&Objects.equals(password, user.password) &&Objects.equals(job, user.job);}@Overridepublic int hashCode() {return Objects.hash(username, password, age, isStudent, job, test1, test2, clazz);}
}

1.6.2 测试类以及测试效果1

package _4控制序列化和反序列化的变量名称.test;import _4控制序列化和反序列化的变量名称.User;
import com.google.gson.Gson;
import com.google.gson.GsonBuilder;public class TestVariableNameOfControllSerializeAndDeserialize {public static void main(String[] args) {User user1 = new User("zhangsan","123",18,false);user1.setTest1(1);user1.setTest2(2);user1.setClazz(3);Gson gson = new GsonBuilder().excludeFieldsWithoutExposeAnnotation().create();//让@Expose注解生效String user1Json = gson.toJson(user1);//序列化System.out.println("序列化："+user1Json);User user2 = gson.fromJson(user1Json, User.class);System.out.println("反序列化："+user2);}
}

测试效果

1.6.3 测试类以及测试效果2

package _4控制序列化和反序列化的变量名称.test;import _4控制序列化和反序列化的变量名称.Job;
import _4控制序列化和反序列化的变量名称.User;
import com.google.gson.Gson;
import com.google.gson.GsonBuilder;import java.math.BigDecimal;public class TestVariableNameOfControllSerializeAndDeserialize02 {public static void main(String[] args) {User user1 = new User("zhangsan","123",18,false);user1.setTest1(1);user1.setTest2(2);user1.setClazz(3);Job job = new Job("Java开发",new BigDecimal(10000.00));user1.setJob(job);Gson gson  =new GsonBuilder().excludeFieldsWithoutExposeAnnotation().create();//让@Expose注解生效String user1Json = gson.toJson(user1);//序列化System.out.println("序列化："+user1Json);User user2 = gson.fromJson(user1Json, User.class);//反序列化System.out.println("反序列化："+user2);}
}

测试效果

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