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内容:所有原创文章分类和汇总,及配套源码,涉及Java、Docker、Kubernetes、DevOPS等;
全系列源码下载整个《jackson学习》系列的源码都可以在GitHub下载,地址和链接信息如下表所示(
):这个git项目中有多个文件夹,《K8S官方java客户端》系列的源码在jacksondemo文件夹下,如下图红框所示:本篇概览
本文是《jackson学习》系列的第三篇,前面咱们学习了jackson的低阶API,知道了底层原理,本篇开始学习平时最常用的基本功能,涉及内容如下:
体验最常用的操作,内容如下图所示:介绍常用的可配置属性,以便按需要来设置;接下来进入快速浏览的环节,咱们一起先把各个API过一遍;单个对象序列化
先看常用的序列化API:
对象转字符串:
String jsonStr = mapper.writeValueAsString(twitterEntry);对象转文件:
mapper.writeValue(new File("twitter.json"), twitterEntry);对象转byte数组:
byte[] array = mapper.writeValueAsBytes(twitterEntry);单个对象反序列化字符串转对象:
TwitterEntry tFromStr = mapper.readValue(objectJsonStr, TwitterEntry.class);文件转对象:
TwitterEntry tFromFile = mapper.readValue(new File("twitter.json"), TwitterEntry.class);byte数组转对象:
TwitterEntry tFromBytes = mapper.readValue(array, TwitterEntry.class);字符串网络地址转对象:
String testJsonDataUrl = ";;TwitterEntry tFromUrl = mapper.readValue(new URL(testJsonDataUrl), TwitterEntry.class);集合序列化HashMap转字符串:
String mapJsonStr = mapper.writeValueAsString(map);集合反序列化字符串转HashMap:
Map<String, Object> mapFromStr = mapper.readValue(mapJsonStr, new TypeReference<Map<String, Object>>() {});JsonNode如果您不想使用XXX.class来做反序列化,也能使用JsonNode来操作:
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();时间字段格式化对于Date字段,默认的反序列化是时间戳,可以修改配置:
mapper.setDateFormat(new SimpleDateFormat("yyyy-MM-dd hh:mm:ss"));dateMapStr = mapper.writeValueAsString(dateMap);JSON数组的反序列化
假设jsonArrayStr是个json数组格式的字符串:
JSON数组转对象数组:
TwitterEntry[] twitterEntryArray = mapper.readValue(jsonArrayStr, TwitterEntry[].class);JSON数组转对象集合(ArrayList):
List<TwitterEntry> twitterEntryList = mapper.readValue(jsonArrayStr, new TypeReference<List<TwitterEntry>>() {});完整代码上述所有常用API用法的完整代码如下:
package com.bolingcavalry.jacksondemo.databind;import com.bolingcavalry.jacksondemo.beans.TwitterEntry;import com.fasterxml.jackson.core.type.TypeReference;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 = ";; 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); }}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.SimpleDemo2020-08-28 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, 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:
序列化结果格式化:
mapper.enable(SerializationFeature.INDENT_OUTPUT);空对象不要抛出异常:
mapper.disable(SerializationFeature.FAIL_ON_EMPTY_BEANS);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);反序列化时,遇到未知属性不要抛出异常:
mapper.disable(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES);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);允许C和C++样式注释:
mapper.configure(JsonParser.Feature.ALLOW_COMMENTS, true);允许字段名没有引号(可以进一步减小json体积):
mapper.configure(JsonParser.Feature.ALLOW_UNQUOTED_FIELD_NAMES, true);允许单引号:
mapper.configure(JsonParser.Feature.ALLOW_SINGLE_QUOTES, true);特殊配置:在json对象最外层再包裹一层最后要说的是个特殊配置,先来看看正常情况一个普通的序列化结果:
{ "id" : 1, "text" : "aabbcc", "fromUserId" : 456, "toUserId" : 0, "languageCode" : "zh"}接下来咱们做两件事,首先,是给上述json对应的实例类添加一个注解,如下图红框:其次,执行以下配置:
mapper.enable(SerializationFeature.WRAP_ROOT_VALUE);然后再次执行TwitterEntry实例的序列化,得到的结果如下,可见和之前的序列化结果相比,之前的整个json都变成了一个value,此value对应的key就是注解JsonRootName的value属性:
{ "aaa" : { "id" : 1, "text" : "aabbcc", "fromUserId" : 456, "toUserId" : 0, "languageCode" : "zh" }}至此,开发中常用的API和配置都已经介绍完成,希望能给您带来一些参考,接下来的章节,咱们一起去了解另一个常用操作:jackson注解;欢迎关注我的公众号:程序员欣宸
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