jackson 学习之二：jackson-core

3. 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+"]";

}}

4. 以上就是准备工作了，接下来开始实战 jackson-core；

[](()JsonFactory 线程安全吗?

1. 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；

2. 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 《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》无偿开源 威信搜索公众号【编程进阶路】 档地址：http://fasterxml.github.io/jackson-core/javadoc/2.11/

[](()jackson-core 实战

1. 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 http://maven.apache.org/xsd/maven-4.0.0.xsd">

<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>

2. 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();