JsonPath：使用List成员将JSON解析为Java对象

Question

I am trying to parse the following JSON into Book class:

{
  "inventory": {
      "book": {
          "title": "Database Systems",
           "authors": [
              {"name": "Sudarshan"},
              {"name": "Korth"},
              {"name": "Silberschatz"}
           ]
       }
  }
}

Book class which has JSON annotations for the fields and has the following definition:

package com.example.books    

public class Book {

    @JsonProperty("title")
    private String title;

    @JsonProperty("authors")
    private List<Author> authors;

    public Book() {
        authors = new ArrayList<Author>();
    }
    // constructors, getters, setters

}     

public class Author {
    @JsonProperty
    private String name;

    // constructor, getters, setters...

}

I am trying to achieve this using com.jayway.jsonpath.JsonPath :

Book book = JsonPath.read(inventoryJson.toString(), "$.inventory.book");

This results in the following exception:

java.lang.ClassCastException: java.util.LinkedHashMap cannot be cast to com.example.books.Book

I have also tried:

Book book = JsonPath.parse(inventoryJson.toString()).read("$.inventory.book", Book.class);

This one now gives a different exception:

java.lang.RuntimeException: Can not find Array 'authors' field in class com.example.book.Book
    at net.minidev.json.writer.BeansMapper$Bean.startArray(BeansMapper.java:79)
    at net.minidev.json.parser.JSONParserBase.readMain(JSONParserBase.java:402)
    at net.minidev.json.parser.JSONParserBase.readObject(JSONParserBase.java:542)
    at net.minidev.json.parser.JSONParserBase.readFirst(JSONParserBase.java:297)
    at net.minidev.json.parser.JSONParserBase.parse(JSONParserBase.java:154)
    at net.minidev.json.parser.JSONParserString.parse(JSONParserString.java:58)
    at net.minidev.json.parser.JSONParser.parse(JSONParser.java:263)
    at net.minidev.json.JSONValue.parse(JSONValue.java:206)
    at com.jayway.jsonpath.spi.mapper.JsonSmartMappingProvider.map(JsonSmartMappingProvider.java:82)
    at com.jayway.jsonpath.internal.JsonContext.convert(JsonContext.java:192)
    at com.jayway.jsonpath.internal.JsonContext.read(JsonContext.java:158)

How do I make it work?

Original classes:
http://pastebin.com/SAhipfxL
http://pastebin.com/vWfWsaqN
http://pastebin.com/7tqhJfw3

Complete stack trace: http://pastebin.com/QWV89Hgj

Answer 1

I found series of mistakes in code from your question.

Let's start from json itself: it is not well-formed in exactly that view, which you've provided.

It should be:

{
"inventory": {
    "books": {
        "title": "Database Systems",
        "authors": [
            {"name": "Sudarshan"},
            {"name": "Korth"},
            {"name": "Silberschatz"}
         ]
     }
 }
}

Notice also please, that it should be " books " instead of " book ".

Next problem is that you've declared classes Book and Author as package local. This won't work. Consider making them public or public static at least.

These fixes will solve your problem, for second statement:

Book book = JsonPath.parse(inventoryJson.toString()).read("$.inventory.books", Book.class); - it should work properly.