使用Json的对象列表

Question

我在Deck类中创建一个问题对象列表。我读取Json文件并将其传递给String，然后简单地使用Gson创建对象列表。但那不起作用：/你有谢谢你的主意吗。这是我的Json文件：

{
    "questions": [{
            "author": "Florian Genicq",
            "category": "NETWORK",
            "statement": "What stands for LAN?",
            "answer": "Local Area Network"
        },
        {
            "author": "Florian Genicq",
            "category": "NETWORK",
            "statement": "Which network requires terminators?",
            "answer": "BUS network"
        },
        {
            "author": "Florian Genicq",
            "category": "NETWORK",
            "statement": "Which network topology is fastest?",
            "answer": "Star network"
        },
        {
            "author": "Florian Genicq",
            "category": "NETWORK",
            "statement": "What is the maximum bandwith that can be supported by filter optics cable?(Mbps)",
            "answer": 2000
        },
        {
            "author": "Florian Genicq",
            "category": "Operating System",
            "statement": "Which operating system doesn’t support networking computers?",
            "answer": "Windows 3.1"
        },
        {
            "author": "Florian Genicq",
            "category": "Operating System",
            "statement": "Usuallu, in MSDOS, the primary hard disk drives has the drive letter ___",
            "answer": "C"
        },
        {
            "author": "Médéric Allard",
            "category": "Social Network",
            "statement": "How many characters can you use on Twitter?",
            "answer": 280
        },
        {
            "author": "Médéric Allard",
            "category": "Operating System",
            "statement": "How many characters can you use on Twitter?",
            "answer": 280

        }

    ]
}

这是我的问题构造器：

private String author,statement,answer;
private Category category;

public Question(String au,Category c,String s,String an) {
    this.author=au;
    this.category=c;
    this.statement=s;
    this.answer=an;

}

这是我的甲板建造师：

private List<Question> listQuestion;

public Deck() {
    listQuestion = new ArrayList<>();
}

这是我的主要代码：

Gson gson = new Gson();
String res1  = JsonTransform.readFromFile("/json.json", true);
//System.out.println(res1);
Deck res2 = gson.fromJson(res1, Deck.class);
System.out.println(res2);

res1是我以字符串格式获得的Json文件，因此res2应该包含一个与Json文件相关的对象列表，但列表中没有任何内容。

Answer 1

我不确定JsonTransform类是什么，所以不能对此进行评论，但下面的代码可以正常工作。问题是您应该将deck类的listquestion变量名更改为questions或使用属性@serializedName（“questions”）进行注释；

下面是相同的完整代码。我已经使用BufferedReader从文件中读取json

课堂问题

import java.util.List;

/**
 * @author Utkarsh Thusoo
 * @version $Id: $
 */
public class Questions
{

    private String author;

    private String category;

    private String statement;

    private String answer;

    /**
     * @return the author
     */
    public String getAuthor()
    {
        return author;
    }

    /**
     * @param author
     *            the author to set
     */
    public void setAuthor(String author)
    {
        this.author = author;
    }

    /**
     * @return the category
     */
    public String getCategory()
    {
        return category;
    }

    /**
     * @param category
     *            the category to set
     */
    public void setCategory(String category)
    {
        this.category = category;
    }

    /**
     * @return the statement
     */
    public String getStatement()
    {
        return statement;
    }

    /**
     * @param statement
     *            the statement to set
     */
    public void setStatement(String statement)
    {
        this.statement = statement;
    }

    /**
     * @return the answer
     */
    public String getAnswer()
    {
        return answer;
    }

    /**
     * @param answer
     *            the answer to set
     */
    public void setAnswer(String answer)
    {
        this.answer = answer;
    }

    /** 
     * @inheritDoc
     */
    @Override
    public String toString()
    {
        return "Questions [author=" + author + ", category=" + category + ", statement=" + statement
                + ", answer=" + answer + "]";
    }



}

级甲板

/**
 * @author Utkarsh Thusoo
 * @version $Id: $
 */
public class Deck
{

    private List<Questions> questions;

    /**
     * @return the questions
     */
    public List<Questions> getQuestions()
    {
        return questions;
    }

    /**
     * @param questions the questions to set
     */
    public void setQuestions(List<Questions> questions)
    {
        this.questions = questions;
    }

    /** 
     * @inheritDoc
     */
    @Override
    public String toString()
    {
        return "Deck [questions=" + questions + "]";
    }


}

测试类

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;

import com.google.gson.Gson;

public class Test
{

    public static void main(String[] args) throws IOException
    {
        Gson gson = new Gson();
        BufferedReader br = new BufferedReader(new FileReader("json.json"));
        StringBuffer res1 = new StringBuffer();

        String currLine = "";
        while((currLine = br.readLine())!=null){
            res1.append(currLine); 
        }


        Deck res2 = gson.fromJson(res1.toString(), Deck.class);
        System.out.println(res2);

    }

}

输出

Deck [questions=[Questions [author=Florian Genicq, category=NETWORK, statement=What stands for LAN?, answer=Local Area Network], Questions [author=Florian Genicq, category=NETWORK, statement=Which network requires terminators?, answer=BUS network], Questions [author=Florian Genicq, category=NETWORK, statement=Which network topology is fastest?, answer=Star network], Questions [author=Florian Genicq, category=NETWORK, statement=What is the maximum bandwith that can be supported by filter optics cable?(Mbps), answer=2000], Questions [author=Florian Genicq, category=Operating System, statement=Which operating system doesn’t support networking computers?, answer=Windows 3.1], Questions [author=Florian Genicq, category=Operating System, statement=Usuallu, in MSDOS, the primary hard disk drives has the drive letter ___, answer=C], Questions [author=Médéric Allard, category=Social Network, statement=How many characters can you use on Twitter?, answer=280], Questions [author=Médéric Allard, category=Operating System, statement=How many characters can you use on Twitter?, answer=280]]]