增加一个Pojo，对应的是一条推特消息：
package com.bolingcavalry.jacksondemo.beans; /** * @Description: 推特消息bean * @author: willzhao E-mail: zq2599@gmail.com * @date: 2020/7/4 16:24 */ public class TwitterEntry { /** * 推特消息id */ long id; /** * 消息内容 */ String text; /** * 消息创建者 */ int fromUserId; /** * 消息接收者 */ int toUserId; /** * 语言类型 */ String languageCode; public long getId() { return id; } public void setId(long id) { this.id = id; } public String getText() { return text; } public void setText(String text) { this.text = text; } public int getFromUserId() { return fromUserId; } public void setFromUserId(int fromUserId) { this.fromUserId = fromUserId; } public int getToUserId() { return toUserId; } public void setToUserId(int toUserId) { this.toUserId = toUserId; } public String getLanguageCode() { return languageCode; } public void setLanguageCode(String languageCode) { this.languageCode = languageCode; } public TwitterEntry() { } public String toString() { return "[Tweet, id: "+id+", text='"+text+"', from: "+fromUserId+", to: "+toUserId+", lang: "+languageCode+"]"; }}以上就是准备工作了，接下来开始实战jackson-core；
JsonFactory线程安全吗?JsonFactory是否是线程安全的，这是编码前要弄清楚的问题，因为JsonParser和JsonGenerator的创建都离不开JsonFactory；
如下图红框所示，jackson官方文档中明确指出JsonFactory是线程安全的，可以放心的作为全局变量给多线程同时使用：
3. 官方文档地址： jackson-core实战
新建子工程core，pom.xml如下：
<?xml version="1.0" encoding="UTF-8"?> <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 "> <parent> <artifactId>jacksondemo</artifactId> <groupId>com.bolingcavalry</groupId> <version>1.0-SNAPSHOT</version> <relativePath>../pom.xml</relativePath> </parent> <modelVersion>4.0.0</modelVersion> <groupId>com.bolingcavalry</groupId> <artifactId>core</artifactId> <name>core</name> <description>Demo project for jackson core use</description> <build> <plugins> <plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-compiler-plugin</artifactId> <configuration> <source>8</source> <target>8</target> </configuration> </plugin> </plugins> </build> <dependencies> <dependency> <groupId>com.fasterxml.jackson.core</groupId> <artifactId>jackson-databind</artifactId> </dependency> <dependency> <groupId>org.slf4j</groupId> <artifactId>slf4j-log4j12</artifactId> </dependency> <dependency> <groupId>commons-io</groupId> <artifactId>commons-io</artifactId> </dependency> <dependency> <groupId>org.apache.commons</groupId> <artifactId>commons-lang3</artifactId> </dependency> <dependency> <groupId>com.bolingcavalry</groupId> <artifactId>beans</artifactId> <version>${project.version}</version> </dependency> </dependencies> </project>新建StreamingDemo类，这里面是调用jackson-core的API进行序列化和反序列化的所有demo，如下：
package com.bolingcavalry.jacksondemo.core; import com.bolingcavalry.jacksondemo.beans.TwitterEntry; import com.fasterxml.jackson.core.*; import com.fasterxml.jackson.databind.ObjectMapper; import org.apache.commons.io.IOUtils; import org.apache.commons.lang3.StringUtils; import org.slf4j.Logger; import org.slf4j.LoggerFactory; import java.io.ByteArrayOutputStream; import java.io.IOException; import java.net.URL; /** * @Description: jackson低阶方法的使用 * @author: willzhao E-mail: zq2599@gmail.com * @date: 2020/7/4 15:50 */ public class StreamingDemo { private static final Logger logger = LoggerFactory.getLogger(StreamingDemo.class); JsonFactory jsonFactory = new JsonFactory(); /** * 该字符串的值是个网络地址，该地址对应的内容是个JSON */ final static String TEST_JSON_DATA_URL = "https://raw.githubusercontent.com/zq2599/blog_demos/master/files/twitteer_message.json"; /** * 用来验证反序列化的JSON字符串 */ final static String TEST_JSON_STR = "{\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" + "}"; /** * 用来验证序列化的TwitterEntry实例 */ final static TwitterEntry TEST_OBJECT = new TwitterEntry(); /** * 准备好TEST_OBJECT对象的各个参数 */ static { TEST_OBJECT.setId(123456L); TEST_OBJECT.setFromUserId(101); TEST_OBJECT.setToUserId(102); TEST_OBJECT.setText("this is a message for serializer test"); TEST_OBJECT.setLanguageCode("zh"); } /** * 反序列化测试(JSON -> Object)，入参是JSON字符串 * @param json JSON字符串 * @return * @throws IOException */ public TwitterEntry deserializeJSONStr(String json) throws IOException { JsonParser jsonParser = jsonFactory.createParser(json); if (jsonParser.nextToken() != JsonToken.START_OBJECT) { jsonParser.close(); logger.error("起始位置没有大括号"); throw new IOException("起始位置没有大括号"); } TwitterEntry result = new TwitterEntry(); try { // Iterate over object fields: while (jsonParser.nextToken() != JsonToken.END_OBJECT) { String fieldName = jsonParser.getCurrentName(); logger.info("正在解析字段 [{}]", jsonParser.getCurrentName()); // 解析下一个 jsonParser.nextToken(); switch (fieldName) { case "id": result.setId(jsonParser.getLongValue()); break; case "text": result.setText(jsonParser.getText()); break; case "fromUserId": result.setFromUserId(jsonParser.getIntValue()); break; case "toUserId": result.setToUserId(jsonParser.getIntValue()); break; case "languageCode": result.setLanguageCode(jsonParser.getText()); break; default: logger.error("未知字段 '" + fieldName + "'"); throw new IOException("未知字段 '" + fieldName + "'"); } } } catch (IOException e) { logger.error("反序列化出现异常 :", e); } finally { jsonParser.close(); // important to close both parser and underlying File reader } return result; } /** * 反序列化测试(JSON -> Object)，入参是JSON字符串 * @param url JSON字符串的网络地址 * @return * @throws IOException */ public TwitterEntry deserializeJSONFromUrl(String url) throws IOException { // 从网络上取得JSON字符串 String json = IOUtils.toString(new URL(TEST_JSON_DATA_URL), JsonEncoding.UTF8.name()); logger.info("从网络取得JSON数据 :\n{}", json); if(StringUtils.isNotBlank(json)) { return deserializeJSONStr(json); } else { logger.error("从网络获取JSON数据失败"); return null; } } /** * 序列化测试(Object -> JSON) * @param twitterEntry * @return 由对象序列化得到的JSON字符串 */ public String serialize(TwitterEntry twitterEntry) throws IOException{ String rlt = null; ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream(); JsonGenerator jsonGenerator = jsonFactory.createGenerator(byteArrayOutputStream, JsonEncoding.UTF8); try { jsonGenerator.useDefaultPrettyPrinter(); jsonGenerator.writeStartObject(); jsonGenerator.writeNumberField("id", twitterEntry.getId()); jsonGenerator.writeStringField("text", twitterEntry.getText()); jsonGenerator.writeNumberField("fromUserId", twitterEntry.getFromUserId()); jsonGenerator.writeNumberField("toUserId", twitterEntry.getToUserId()); jsonGenerator.writeStringField("languageCode", twitterEntry.getLanguageCode()); jsonGenerator.writeEndObject(); } catch (IOException e) { logger.error("序列化出现异常 :", e); } finally { jsonGenerator.close(); } // 一定要在 rlt = byteArrayOutputStream.toString(); return rlt; } public static void main(String[] args) throws Exception { StreamingDemo streamingDemo = new StreamingDemo(); // 执行一次对象转JSON操作 logger.info("********************执行一次对象转JSON操作********************"); String serializeResult = streamingDemo.serialize(TEST_OBJECT); logger.info("序列化结果是JSON字符串 : \n{}\n\n", serializeResult); // 用本地字符串执行一次JSON转对象操作 logger.info("********************执行一次本地JSON反序列化操作********************"); TwitterEntry deserializeResult = streamingDemo.deserializeJSONStr(TEST_JSON_STR); logger.info("\n本地JSON反序列化结果是个java实例 : \n{}\n\n", deserializeResult); // 用网络地址执行一次JSON转对象操作 logger.info("********************执行一次网络JSON反序列化操作********************"); deserializeResult = streamingDemo.deserializeJSONFromUrl(TEST_JSON_DATA_URL); logger.info("\n网络JSON反序列化结果是个java实例 : \n{}", deserializeResult); ObjectMapper a; } }上述代码可见JsonParser负责将JSON解析成对象的变量值，核心是循环处理JSON中的所有内容；
JsonGenerator负责将对象的变量写入JSON的各个属性，这里是开发者自行决定要处理哪些字段；