jackson 学习之二:jackson-core
public class Constant {
/**
该字符串的值是个网络地址,该地址对应的内容是个 JSON
*/
public 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
*/
public 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
*/
p
ublic 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");
}}
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:
官方文档地址:http://fasterxml.github.io/jackson-core/javadoc/2.11/
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 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>
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();
}
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