Java下常见的Json类库有Gson、JSON-lib和Jackson等，Jackson相对来说比较高效，在项目中主要使用Jackson进行JSON和Java对象转换，下面给出一些Jackson的JSON操作方法。
一、准备工作
Jackson有1.x系列和2.x系列，2.x系列有3个jar包需要下载：
jackson-core-2.2.3.jar（核心jar包）jackson-annotations-2.2.3.jar（该包提供Json注解支持）jackson-databind-2.2.3.jar一个maven依赖就够了
com.fasterxml.jackson.core jackson-databind 2.5.3
import java.util.Date;/** * JSON序列化和反序列化使用的User类 */public class User { private String name; private Integer age; private Date birthday; private String email; public String getName() { return name; } public void setName(String name) { this.name = name; } public Integer getAge() { return age; } public void setAge(Integer age) { this.age = age; } public Date getBirthday() { return birthday; } public void setBirthday(Date birthday) { this.birthday = birthday; } public String getEmail() { return email; } public void setEmail(String email) { this.email = email; } @Override public String toString() { return "User{" + "name='" + name + '\'' + ", age=" + age + ", birthday=" + birthday + ", email='" + email + '\'' + '}'; }} 二、JAVA对象转JSON[JSON序列化]
import java.io.IOException;import java.text.ParseException;import java.text.SimpleDateFormat;import java.util.ArrayList;import java.util.List;import com.fasterxml.jackson.databind.ObjectMapper;public class JacksonDemo { public static void main(String[] args) throws ParseException, IOException { User user = new User(); user.setName("zhangsan"); user.setEmail("zhangsan@163.com"); user.setAge(20); SimpleDateFormat dateformat = new SimpleDateFormat("yyyy-MM-dd"); user.setBirthday(dateformat.parse("1996-10-01")); /** * ObjectMapper是JSON操作的核心，Jackson的所有JSON操作都是在ObjectMapper中实现。 * ObjectMapper有多个JSON序列化的方法，可以把JSON字符串保存File、OutputStream等不同的介质中。 * writeValue(File arg0, Object arg1)把arg1转成json序列，并保存到arg0文件中。 * writeValue(OutputStream arg0, Object arg1)把arg1转成json序列，并保存到arg0输出流中。 * writeValueAsBytes(Object arg0)把arg0转成json序列，并把结果输出成字节数组。 * writeValueAsString(Object arg0)把arg0转成json序列，并把结果输出成字符串。 */ ObjectMapper mapper = new ObjectMapper(); //User类转JSON //输出结果：{"name":"zhangsan","age":20,"birthday":844099200000,"email":"zhangsan@163.com"} String json = mapper.writeValueAsString(user); System.out.println(json); //Java集合转JSON //输出结果：[{"name":"zhangsan","age":20,"birthday":844099200000,"email":"zhangsan@163.com"}] List users = new ArrayList (); users.add(user); String jsonlist = mapper.writeValueAsString(users); System.out.println(jsonlist); }} 三、JSON转Java类[JSON反序列化]
public class JacksonDemo { public static void main(String[] args) throws ParseException, IOException { String json = "{\"name\":\"zhangsan\",\"age\":20,\"birthday\":844099200000,\"email\":\"zhangsan@163.com\"}"; /** * ObjectMapper支持从byte[]、File、InputStream、字符串等数据的JSON反序列化。 */ ObjectMapper mapper = new ObjectMapper(); User user = mapper.readValue(json, User.class); System.out.println(user); }} 结果
User{name='zhangsan', age=20, birthday=Tue Oct 01 00:00:00 CST 1996, email='zhangsan@163.com'} public class JacksonDemo { public static ObjectMapper mapper = new ObjectMapper(); public static void main(String[] args) throws ParseException, IOException { String json = "[{\"name\":\"zhangsan\",\"age\":20,\"birthday\":844099200000,\"email\":\"zhangsan@163.com\"}]"; List beanList = mapper.readValue(json, new TypeReference >() {}); System.out.println(beanList); }}
结果
[User{name='zhangsan', age=20, birthday=Tue Oct 01 00:00:00 CST 1996, email='zhangsan@163.com'}] 四、JSON注解
Jackson提供了一系列注解，方便对JSON序列化和反序列化进行控制，下面介绍一些常用的注解。
@JsonIgnore 此注解用于属性上，作用是进行JSON操作时忽略该属性。@JsonFormat 此注解用于属性上，作用是把Date类型直接转化为想要的格式，如@JsonFormat(pattern = "yyyy-MM-dd HH-mm-ss")。@JsonProperty 此注解用于属性上，作用是把该属性的名称序列化为另外一个名称，如把trueName属性序列化为name，@JsonProperty("name")。import com.fasterxml.jackson.annotation.JsonFormat;import com.fasterxml.jackson.annotation.JsonIgnore;import com.fasterxml.jackson.annotation.JsonProperty;import java.util.Date;/** * JSON序列化和反序列化使用的User类 */public class User { private String name; //不JSON序列化年龄属性 @JsonIgnore private Integer age; //格式化日期属性 @JsonFormat(pattern = "yyyy年MM月dd日") private Date birthday; //序列化email属性为mail @JsonProperty("my_email") private String email; public String getName() { return name; } public void setName(String name) { this.name = name; } public Integer getAge() { return age; } public void setAge(Integer age) { this.age = age; } public Date getBirthday() { return birthday; } public void setBirthday(Date birthday) { this.birthday = birthday; } public String getEmail() { return email; } public void setEmail(String email) { this.email = email; } @Override public String toString() { return "User{" + "name='" + name + '\'' + ", age=" + age + ", birthday=" + birthday + ", email='" + email + '\'' + '}'; }} import com.fasterxml.jackson.databind.ObjectMapper;import java.io.IOException;import java.text.ParseException;import java.text.SimpleDateFormat;public class JacksonDemo { public static void main(String[] args) throws ParseException, IOException { User user = new User(); user.setName("zhangsan"); user.setEmail("zhangsan@163.com"); user.setAge(20); SimpleDateFormat dateformat = new SimpleDateFormat("yyyy-MM-dd"); user.setBirthday(dateformat.parse("1996-10-01")); ObjectMapper mapper = new ObjectMapper(); String json = mapper.writeValueAsString(user); System.out.println(json); }} {"name":"zhangsan","birthday":"1996年09月30日","my_email":"zhangsan@163.com"}
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