記一次FastJSON和Jackson解析json時遇到的中括號問題

完整版見https://jadyer.github.io/

先列出來正確的解析代碼，接着再描述問題詳情。

首先是用到的JavaBean

package com.jadyer.model;

public class User {
	private String name;
	private Book book;
	
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public Book getBook() {
		return book;
	}
	public void setBook(Book book) {
		this.book = book;
	}
}

package com.jadyer.model;

public class Book {
	private String name;
//	private List<Author> author = new ArrayList<Author>();
	private Author author;
	
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
//	public List<Author> getAuthor() {
//		return author;
//	}
//	public void setAuthor(List<Author> author) {
//		this.author = author;
//	}
	public Author getAuthor() {
		return author;
	}
	public void setAuthor(Author author) {
		this.author = author;
	}
}

package com.jadyer.model;

public class Author {
	private String name;
	private int money;
	
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public int getMoney() {
		return money;
	}
	public void setMoney(int money) {
		this.money = money;
	}
}

下面是生成json和解析json的代碼

package com.jadyer.main;

import java.io.IOException;

import org.apache.commons.lang3.builder.ReflectionToStringBuilder;
import org.apache.commons.lang3.builder.ToStringStyle;
import org.codehaus.jackson.JsonParseException;
import org.codehaus.jackson.map.JsonMappingException;
import org.codehaus.jackson.map.ObjectMapper;

import com.alibaba.fastjson.JSON;
import com.jadyer.model.User;

public class JSONDemo {
//	/**
//	 * 生成{"book":{"author":[{"money":500,"name":"南派三叔"},{"money":200,"name":"孔二狗"}],"name":"網絡文學"},"name":"玄玉"}
//	 */
//	private static String format(){
//		List<Author> authorList = new ArrayList<Author>();
//		Author author11 = new Author();
//		author11.setName("南派三叔");
//		author11.setMoney(500);
//		authorList.add(author11);
//		Author author22 = new Author();
//		author22.setName("孔二狗");
//		author22.setMoney(200);
//		authorList.add(author22);
//		Book book = new Book();
//		book.setName("網絡文學");
//		book.setAuthor(authorList);
//		User user = new User();
//		user.setName("玄玉");
//		user.setBook(book);
//		return JSON.toJSONString(user);
//	}
	
	public static void main(String[] args) throws JsonParseException, JsonMappingException, IOException {
		String jsonText = "{\"book\":{\"author\":{\"money\":500,\"name\":\"南派三叔\"},\"name\":\"網絡文學\"},\"name\":\"玄玉\"}";
		//用到的jar爲fastjson-1.1.36.jar
		User userFromFastJSON = JSON.parseObject(jsonText, User.class);
		System.out.println(ReflectionToStringBuilder.toString(userFromFastJSON.getBook().getAuthor(), ToStringStyle.MULTI_LINE_STYLE));
		System.out.println("----------------------------------------------------------------------------------");
		//用到的jar爲jackson-all-1.9.11.jar
		User userFromJackson = new ObjectMapper().readValue(jsonText, User.class);
		System.out.println(ReflectionToStringBuilder.toString(userFromJackson.getBook().getAuthor(), ToStringStyle.MULTI_LINE_STYLE));
	}
}

接下來描述下遇到的問題

//上面解析正常時用到的json串
//"{\"book\":{\"author\":{\"money\":500,\"name\":\"南派三叔\"},\"name\":\"網絡文學\"},\"name\":\"玄玉\"}";
//我在用fastjson和jackson解析時都會報錯時用的json串
//"{\"book\":{\"author\":[{\"money\":500,\"name\":\"南派三叔\"}],\"name\":\"網絡文學\"},\"name\":\"玄玉\"}";
//它倆的區別在於:book中只有一個author對象,只是多加了[],但其仍爲合法的json串
//並且http://tool.oschina.net/codeformat/json均驗證通過

但在解析時，FastJSON會報下面的異常

Exception in thread "main" com.alibaba.fastjson.JSONException: syntax error, expect {, actual ], pos 39
	at com.alibaba.fastjson.parser.deserializer.JavaBeanDeserializer.deserialze(JavaBeanDeserializer.java:212)
	at com.alibaba.fastjson.parser.deserializer.ASMJavaBeanDeserializer.parseRest(ASMJavaBeanDeserializer.java:96)
	at Fastjson_ASM_User_1.deserialze(Unknown Source)
	at com.alibaba.fastjson.parser.DefaultJSONParser.parseObject(DefaultJSONParser.java:513)
	at com.alibaba.fastjson.JSON.parseObject(JSON.java:244)
	at com.alibaba.fastjson.JSON.parseObject(JSON.java:220)
	at com.alibaba.fastjson.JSON.parseObject(JSON.java:179)
	at com.alibaba.fastjson.JSON.parseObject(JSON.java:323)
	at com.jadyer.main.JSONDemoDetail.main(JSONDemoDetail.java:18)

Jackson會報下面的異常

Exception in thread "main" org.codehaus.jackson.map.JsonMappingException: Can not deserialize instance of com.jadyer.model.Author out of START_ARRAY token
 at [Source: java.io.StringReader@509ced8e; line: 1, column: 10] (through reference chain: com.jadyer.model.User["book"]->com.jadyer.model.Book["author"])
	at org.codehaus.jackson.map.JsonMappingException.from(JsonMappingException.java:163)
	at org.codehaus.jackson.map.deser.StdDeserializationContext.mappingException(StdDeserializationContext.java:219)
	at org.codehaus.jackson.map.deser.StdDeserializationContext.mappingException(StdDeserializationContext.java:212)
	at org.codehaus.jackson.map.deser.BeanDeserializer.deserializeFromArray(BeanDeserializer.java:875)
	at org.codehaus.jackson.map.deser.BeanDeserializer.deserialize(BeanDeserializer.java:597)
	at org.codehaus.jackson.map.deser.SettableBeanProperty.deserialize(SettableBeanProperty.java:299)
	at org.codehaus.jackson.map.deser.SettableBeanProperty$MethodProperty.deserializeAndSet(SettableBeanProperty.java:414)
	at org.codehaus.jackson.map.deser.BeanDeserializer.deserializeFromObject(BeanDeserializer.java:697)
	at org.codehaus.jackson.map.deser.BeanDeserializer.deserialize(BeanDeserializer.java:580)
	at org.codehaus.jackson.map.deser.SettableBeanProperty.deserialize(SettableBeanProperty.java:299)
	at org.codehaus.jackson.map.deser.SettableBeanProperty$MethodProperty.deserializeAndSet(SettableBeanProperty.java:414)
	at org.codehaus.jackson.map.deser.BeanDeserializer.deserializeFromObject(BeanDeserializer.java:697)
	at org.codehaus.jackson.map.deser.BeanDeserializer.deserialize(BeanDeserializer.java:580)
	at org.codehaus.jackson.map.ObjectMapper._readMapAndClose(ObjectMapper.java:2732)
	at org.codehaus.jackson.map.ObjectMapper.readValue(ObjectMapper.java:1863)
	at com.jadyer.main.JSONDemoDetail.main(JSONDemoDetail.java:22)

個人感覺Jackson的異常看上去更直觀，可能是二者內部的驗證邏輯不同導致的

不過還是傾向於FastJSON，即便一時之間沒看明白它的異常描述，但那也只是這方面的經驗不足而已

下面說一下解決辦法：Book.java中將author修改爲List<Author>類型的屬性，並添加對應的setter和getter即可

個人的理解是：FastJSON和Jackson解析json爲JavaBean時，先查看實體類的對應屬性

當發現該屬性不能承載多個對象值，且json串中恰好該屬性使用的是中括號，這並不是它預期的大括號，於是報錯了