jackson学习之二:jackson-core
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关于jackson-core
- 本文主要内容是==jackson-core库==,这是个低阶API库,提供流式解析工具==JsonParser==,流式生成工具==JsonGenerator==;
- 在日常的序列化和反序列化处理中,最常用的是==jackson-annotations==和==jackson-databind==,而jackson-core由于它提供的API过于基础,我们大多数情况下是用不上的;
- 尽管jackson-databind负责序列化和反序列化处理,但它的底层实现是调用了jackson-core的API;
- 本着万丈高楼平地起的原则,本文咱们通过实战了解神秘的jackson-core,了解整个jackson的序列化和反序列化基本原理;
源码下载
- 如果您不想编码,可以在GitHub下载所有源码,地址和链接信息如下表所示(https://github.com/zq2599/blog_demos):
名称 | 链接 | 备注 |
---|---|---|
项目主页 | https://github.com/zq2599/blog_demos | 该项目在GitHub上的主页 |
git仓库地址(https) | https://github.com/zq2599/blog_demos.git | 该项目源码的仓库地址,https协议 |
git仓库地址(ssh) | git@github.com:zq2599/blog_demos.git | 该项目源码的仓库地址,ssh协议 |
- 这个git项目中有多个文件夹,本章的应用在==jacksondemo==文件夹下,如下图红框所示:
创建父子工程
创建名为==jacksondemo==的maven工程,这是个父子结构的工程,其pom.xml内容如下:
<?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 https://maven.apache.org/xsd/maven-4.0.0.xsd"> <modelVersion>4.0.0</modelVersion> <properties> <java.version>1.8</java.version> </properties> <groupId>com.bolingcavalry</groupId> <artifactId>jacksondemo</artifactId> <version>1.0-SNAPSHOT</version> <packaging>pom</packaging> <modules> <module>core</module> <module>beans</module> <module>databind</module> </modules> <dependencyManagement> <dependencies> <dependency> <groupId>com.fasterxml.jackson.core</groupId> <artifactId>jackson-databind</artifactId> <version>2.11.0</version> <scope>compile</scope> </dependency> <dependency> <groupId>org.slf4j</groupId> <artifactId>slf4j-log4j12</artifactId> <version>1.7.25</version> <scope>compile</scope> </dependency> <dependency> <groupId>commons-io</groupId> <artifactId>commons-io</artifactId> <version>2.7</version> <scope>compile</scope> </dependency> <dependency> <groupId>org.apache.commons</groupId> <artifactId>commons-lang3</artifactId> <version>3.10</version> <scope>compile</scope> </dependency> </dependencies> </dependencyManagement> </project>
新增子工程beans
- 在父工程jscksondemo下新增名为==beans==的子工程,这里面是一些常量和Pojo类;
- 增加定义常量的类Constant.java:
package com.bolingcavalry.jacksondemo.beans;
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 cant 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
*/
public 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");
3. 增加一个Pojo,对应的是一条推特消息: ```java 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: ![在这里插入图片描述](https://s4.51cto.com/images/blog/202201/20234340_61e9832c6885a13963.png?x-oss-process=image/watermark,size_14,text_QDUxQ1RP5Y2a5a6i,color_FFFFFF,t_100,g_se,x_10,y_10,shadow_20,type_ZmFuZ3poZW5naGVpdGk=) 3. 官方文档地址: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 <?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;
- 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:
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 StreamingDemoprivate 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 cant 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 IOExceptionJsonParser 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 readerreturn 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;
3. 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; 4. 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; 5. 不论是JsonParser还是JsonGenerator,大家都可以感觉到工作量很大,需要开发者自己动手实现对象和JSON字段的关系映射,实际应用中不需要咱们这样辛苦的编码,jackson的另外两个库(annonation的databind)已经帮我们完成了大量工作,上述代码只是揭示最基础的jackson执行原理; 6. 执行StreamingDemo类,得到结果如下,序列化和反序列化都成功了: ![在这里插入图片描述](https://s4.51cto.com/images/blog/202201/20234340_61e9832c7b61047210.png?x-oss-process=image/watermark,size_14,text_QDUxQ1RP5Y2a5a6i,color_FFFFFF,t_100,g_se,x_10,y_10,shadow_20,type_ZmFuZ3poZW5naGVpdGk=) - 以上就是jackson-core的基本功能,咱们了解了jackson最底层的工作原理,接下来的文章会继续实践更多操作;
- 该字符串的值是个网络地址,该地址对应的内容是个JSON
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