jackson 学习之三：常用 API 操作

import com.fasterxml.jackson.databind.JsonNode;

import com.fasterxml.jackson.databind.ObjectMapper;

import org.slf4j.Logger;

import org.slf4j.LoggerFactory;

import java.io.File;

import java.net.URL;

import java.text.SimpleDateFormat;

import java.util.*;

public class SimpleDemo {

private static final Logger logger = LoggerFactory.getLogger(SimpleDemo.class);

public static void main(String[] args) throws Exception {

ObjectMapper mapper = new ObjectMapper();

logger.info("以下是序列化操作");

// 对象 -> 字符串

TwitterEntry twitterEntry = new TwitterEntry();

twitterEntry.setId(123456L);

twitterEntry.setFromUserId(101);

twitterEntry.setToUserId(102);

twitterEntry.setText("this is a message for serializer test");

twitterEntry.setLanguageCode("zh");

String jsonStr = mapper.writeValueAsString(twitterEntry);

logger.info("序列化的字符串：{}", jsonStr);

// 对象 -> 文件

mapper.writeValue(new File("twitter.json"), twitterEntry);

// 对象 -> byte 数组

byte[] array = mapper.writeValueAsBytes(twitterEntry);

logger.info("\n\n 以下是反序列化操作");

// 字符串 -> 对象

String objectJsonStr = "{\n" +

" "id":1125687077,\n" +

" "text":"@stroughtonsmith You need to add a \"Favourites\" tab to TC/iPhone. Like what TwitterFon did. I can't WAIT for your Twitter App!! :) Any ETA?",\n" +

" "fromUserId":855523, \n" +

" "toUserId":815309,\n" +

" "languageCode":"en"\n" +

"}";

TwitterEntry tFromStr = mapper.readValue(objectJsonStr, TwitterEntry.class);

logger.info("从字符串反序列化的对象：{}", tFromStr);

// 文件 -> 对象

TwitterEntry tFromFile = mapper.readValue(new File("twitter.json"), TwitterEntry.class);

logger.info("从文件反序列化的对象：{}", tFromStr);

// byte 数组 -> 对象

TwitterEntry tFromBytes = mapper.readValue(array, TwitterEntry.class);

logger.info("从 byte 数组反序列化的对象：{}", tFromBytes);

// 字符串网络地址 -> 对象

String testJsonDataUrl = "https://raw.githubusercontent.com/zq2599/blog_demos/master/files/twitteer_message.json";

TwitterEntry tFromUrl = mapper.readValue(new URL(testJsonDataUrl), TwitterEntry.class);

logger.info("从网络地址反序列化的对象：{}", tFromUrl);

logger.info("\n\n 以下是集合序列化操作");

Map<String, Object> map = new HashMap<>();

map.put("name", "tom");

map.put("age", 11);

Map<String, String> addr = new HashMap<>();

addr.put("city","深圳");

addr.put("street", "粤海");

map.put("addr", addr);

String mapJsonStr = mapper.writeValueAsString(map);

logger.info("HashMap 序列化的字符串：{}", mapJsonStr);

logger.info("\n\n 以下是集合反序列化操作");

Map<String, Object> mapFromStr = mapper.readValue(mapJsonStr, new TypeReference<Map<String, Object>>() {});

logger.info("从字符串反序列化的 HashMap 对象：{}", mapFromStr);

// JsonNode 类型操作

JsonNode jsonNode = mapper.readTree(mapJsonStr);

String name = jsonNode.get("name").asText();

int age = jsonNode.get("age").asInt();

String city = jsonNode.get("addr").get("city").asText();

String street = jsonNode.get("addr").get("street").asText();

logger.info("用 JsonNode 对象和 API 反序列化得到的数：name[{}]、age[{}]、city[{}]、street[{}]", name, age, city, street);

// 时间类型格式

Map<String, Object> dateMap = new HashMap<>();

dateMap.put("today", new Date());

String dateMapStr = mapper.writeValueAsString(dateMap);

logger.info("默认的时间序列化：{}", dateMapStr);

// 设置时间格式

mapper.setDateFormat(new SimpleDateFormat("yyyy-MM-dd hh:mm:ss"));

dateMapStr = mapper.writeValueAsString(dateMap);

logger.info("自定义的时间序列化：{}", dateMapStr);

System.out.println(objectJsonStr);

// json 数组

String jsonArrayStr = "[{\n" +

" "id":1,\n" +

" "text":"text1",\n" +

" "fromUserId":11, \n" +

" "toUserId":111,\n" +

" "languageCode":"en"\n" +

"},\n" +

"{\n" +

" "id":2,\n" +

" "text":"text2",\n" +

" "fromUserId":22, \n" +

" "toUserId":222,\n" +

" "languageCode":"zh"\n" +

"},\n" +

"{\n" +

" "id":3,\n" +

" "text":"text3",\n" +

" "fromUserId":33, \n" +

" "toUserId":333,\n" +

" "languageCode":"en"\n" +

"}]";

// json 数组 -> 对象数组

TwitterEntry[] twitterEntryArray = mapper.readValue(jsonArrayStr, TwitterEntry[].class);

logger.info("json 数组反序列化成对象数组：{}", Arrays.toString(twitterEntryArray));

// json 数组 -> 对象集合

List<TwitterEntry> twitterEntryList = mapper.readValue(jsonArrayStr, new TypeReference<List<TwitterEntry>>() {});

logger.info("json 数组反序列化成对象集合：{}", twitterEntryList);

}

}

2. 执行结果如下：

C:\jdk\bin\java.exe -javaagent:C:\sofware\JetBrains\IntelliJIDEA\lib\idea_rt.jar=64570:C:\sofware\JetBrains\IntelliJIDEA\bin -Dfile.encoding=UTF-8 -classpath C:\jdk\jre\lib\charsets.jar;C:\jdk\jre\lib\deploy.jar;C:\jdk\jre\lib\ext\access-bridge-64.jar;C:\jdk\jre\lib\ext\cldrdata.jar;C:\jdk\jre\lib\ext\dnsns.jar;C:\jdk\jre\lib\ext\jaccess.jar;C:\jdk\jre\lib\ext\jfxrt.jar;C:\jdk\jre\lib\ext\localedata.jar;C:\jdk\jre\lib\ext\nashorn.jar;C:\jdk\jre\lib\ext\sunec.jar;C:\jdk\jre\lib\ext\sunjce_provider.jar;C:\jdk\jre\lib\ext\sunmscapi.jar;C:\jdk\jre\lib\ext\sunpkcs11.jar;C:\jdk\jre\lib\ext\zipfs.jar;C:\jdk\jre\lib\javaws.jar;C:\jdk\jre\lib\jce.jar;C:\jdk\jre\lib\jfr.jar;C:\jdk\jre\lib\jfxswt.jar;C:\jdk\jre\lib\jsse.jar;C:\jdk\jre\lib\management-agent.jar;C:\jdk\jre\lib\plugin.jar;C:\jdk\jre\lib\resources.jar;C:\jdk\jre\lib\rt.jar;D:\github\blog_demos\jacksondemo\databind\target\classes;C:\Users\12167.m2\repository\com\fasterxml\jackson\core\jackson-databind\2.11.0\jackson-databind-2.11.0.jar;C:\Users\12167.m2\repository\com\fasterxml\jackson\core\jackson-annotations\2.11.0\jackson-annotations-2.11.0.jar;C:\Users\12167.m2\repository\com\fasterxml\jackson\core\jackson-core\2.11.0\jackson-core-2.11.0.jar;C:\Users\12167.m2\repository\org\slf4j\slf4j-log4j12\1.7.25\slf4j-log4j12-1.7.25.jar;C:\Users\12167.m2\repository\org\slf4j\slf4j-api\1.7.25\slf4j-api-1.7.25.jar;C:\Users\12167.m2\repository\log4j\log4j\1.2.17\log4j-1.2.17.jar;C:\Users\12167.m2\repository\commons-io\commons-io\2.7\commons-io-2.7.jar;C:\Users\12167.m2\repository\org\apache\commons\commons-lang3\3.10\commons-lang3-3.10.jar;D:\github\blog_demos\jacksondemo\beans\target\classes com.bolingcavalry.jacksondemo.databind.SimpleDemo

2020-08-28 07:53:01 INFO SimpleDemo:27 - 以下是序列化操作

2020-08-28 07:53:01 INFO SimpleDemo:38 - 序列化的字符串：{"id":123456,"text":"this is a message for serializer test","fromUserId":101,"toUserId":102,"languageCode":"zh"}

2020-08-28 07:53:01 INFO SimpleDemo:47 -

以下是反序列化操作

2020-08-28 07:53:01 INFO SimpleDemo:60 - 从字符串反序列化的对象：[Tweet, id: 1125687077, text='@stroughtonsmith You need to add a "Favourites" tab to TC/iPhone. Like what TwitterFon did. I can't WAIT for your Twitter App!! :) Any ETA?', from: 855523, to: 815309, lang: en]

2020-08-28 07:53:01 INFO SimpleDemo:64 - 从文件反序列化的对象：[Tweet, id: 1125687077, text='@stroughtonsmith You need to add a "Favourites" tab to TC/iPhone. Like what TwitterFon did. I can't WAIT for your Twitter App!! :) Any ETA?', from: 855523, to: 815309, 《一线大厂 Java 面试题解析+后端开发学习笔记+最新架构讲解视频+实战项目源码讲义》开源 lang: en]

2020-08-28 07:53:01 INFO SimpleDemo:68 - 从 byte 数组反序列化的对象：[Tweet, id: 123456, text='this is a message for serializer test', from: 101, to: 102, lang: zh]

2020-08-28 07:53:04 INFO SimpleDemo:74 - 从网络地址反序列化的对象：[Tweet, id: 112233445566, text='this is a message from zq2599's github', from: 201, to: 202, lang: en]

2020-08-28 07:53:04 INFO SimpleDemo:77 -

以下是集合序列化操作

2020-08-28 07:53:04 INFO SimpleDemo:90 - HashMap 序列化的 Java 开源项目【ali1024.coding.net/public/P7/Java/git】 字符串：{"name":"tom","addr":{"city":"深圳","street":"粤海"},"age":11}

2020-08-28 07:53:04 INFO SimpleDemo:92 -

以下是集合反序列化操作

2020-08-28 07:53:04 INFO SimpleDemo:94 - 从字符串反序列化的 HashMap 对象：{name=tom, addr={city=深圳, street=粤海}, age=11}

2020-08-28 07:53:04 INFO SimpleDemo:103 - 用 JsonNode 对象和 API 反序列化得到的数：name[tom]、age[11]、city[深圳]、street[粤海]

2020-08-28 07:53:04 INFO SimpleDemo:111 - 默认的时间序列化：{"today":1598572384838}

2020-08-28 07:53:04 INFO SimpleDemo:116 - 自定义的时间序列化：{"today":"2020-08-28 07:53:04"}

{

"id":1125687077,

"text":"@stroughtonsmith You need to add a "Favourites" tab to TC/iPhone. Like what TwitterFon did. I can't WAIT for your Twitter App!! :) Any ETA?",

"fromUserId":855523,

"toUserId":815309,

"languageCode":"en"

}

2020-08-28 07:53:04 INFO SimpleDemo:145 - json 数组反序列化成对象数组：[[Tweet, id: 1, text='text1', from: 11, to: 111, lang: en], [Tweet, id: 2, text='text2', from: 22, to: 222, lang: zh], [Tweet, id: 3, text='text3', from: 33, to: 333, lang: en]]

2020-08-28 07:53:04 INFO SimpleDemo:149 - json 数组反序列化成对象集合：[[Tweet, id: 1, text='text1', from: 11, to: 111, lang: en], [Tweet, id: 2, text='text2', from: 22, to: 222, lang: zh], [Tweet, id: 3, text='text3', from: 33, to: 333, lang: en]]

Process finished with exit code 0

3. 还会产生名为 twitter.json 的文件，内容如下：

{"id":123456,"text":"this is a message for serializer test","fromUserId":101,"toUserId":102,"languageCode":"zh"}

[](()常用配置

下面是平时可能用到的自定义配置项目：

1. 序列化结果格式化：

mapper.enable(SerializationFeature.INDENT_OUTPUT);

2. 空对象不要抛出异常：

mapper.disable(SerializationFeature.FAIL_ON_EMPTY_BEANS);

3. Date、Calendar 等序列化为时间格式的字符串(如果不执行以下设置，就会序列化成时间戳格式)：

mapper.disable(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS);

4. 反序列化时，遇到未知属性不要抛出异常：

mapper.disable(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES);

5. 反序列化时，空字符串对于的实例属性为 null：

mapper.enable(DeserializationFeature.ACCEPT_EMPTY_STRING_AS_NULL_OBJECT);

6. 允许 C 和 C++样式注释：

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