jackson（一）基本简介以及使用

1. 简介

jackson1.x版本已经停止维护 jackson2.x版本仍在在维护 2.x不兼容1.x
jackson老版本的包路径：org.codehaus.jackson
jackson新版本的包路径是：com.fasterxml.jackson

jackson新版本主要包含3个模块：

• jackson-core
• jackson-annotations
• jackson-databind databind 依赖 jackson-core, jack-annotations

maven仓库的jar包如下：

2.基本使用

2.1 jar包引入

<!-- https://mvnrepository.com/artifact/com.fasterxml.jackson.core/jackson-databind -->
<dependency>
   <groupId>com.fasterxml.jackson.core</groupId>
   <artifactId>jackson-databind</artifactId>
   <version>2.13.0</version>
</dependency>
<dependency>
   <groupId>org.projectlombok</groupId>
   <artifactId>lombok</artifactId>
   <version>1.18.20</version>
</dependency>

2.2 封装工具类

/**
 * jackson的工具类
 */
public class JacksonUtil {
    private static final ObjectMapper objectMapper;

    static {
        objectMapper = new ObjectMapper();
    }

    /**
     * json字符串 转成 java对象
     *
     * @param json json字符串
     * @param cls  java类型
     * @return {@link T}
     */
    public static <T> T json2Object(String json, Class<T> cls) {
        T t = null;
        try {
            t = objectMapper.readValue(json, cls);
        } catch (JsonProcessingException e) {
            e.printStackTrace();
        }
        return t;
    }

    /**
     * java对象 转成 json字符串
     *
     * @param obj java对象
     * @return {@link String}
     */
    public static String object2Json(Object obj) {
        String json = null;
        try {
            json = objectMapper.writeValueAsString(obj);
        } catch (JsonProcessingException e) {
            e.printStackTrace();
        }
        return json;
    }
}

2.3 测试

/**
 * 测试数据 用户组对象
 */
@Data
@Accessors(chain = true)
public class TestUserGroup {
    private Integer id;
    private String name;
    private List<TestUser> users;
}

/**
 * 测试数据 用户对象
 */
@Data
@Accessors(chain = true)
public class TestUser {
    private Integer id;
    private String name;
    private Integer age;
    private Date createTime;
}

/**
 * 测试入口
 */
public class TestJackson {
    public static void main(String[] args) {
        // 测试数据
        TestUser testUser01 = new TestUser().setId(1).setAge(23).setName("用户一").setCreateTime(new Date());
        TestUser testUser02 = new TestUser().setId(2).setAge(34).setName("用户二");
        List<TestUser> testUsers = new ArrayList<>();
        testUsers.add(testUser01);
        testUsers.add(testUser02);
        TestUserGroup testUserGroup = new TestUserGroup().setId(1).setName("用户组一").setUsers(testUsers);

        // 测试jackson对象序列化 对象转json字符串
        String objJsonStr = JacksonUtil.object2Json(testUserGroup);
        System.out.println("objectToJson >>>: " + objJsonStr);

        // 测试jackson对象反序列化 json字符串转对象
        TestUserGroup restTestUserGroup = JacksonUtil.json2Object(objJsonStr, TestUserGroup.class);
        System.out.println("json2Object >>>: " + restTestUserGroup.toString());
    }
}