Java Google Gson.toJson为何丢失数据

我有五门课：

评论

，

文件

，

文件

，

文件

，

文件

注释

是文本的持有者。

论文

是空的抽象类。

WoundPaper

扩展

Paper

并存储字符串和

注释的数组列表

---

Document

是一个抽象类，当gson对

WoundDoc

进行序列化时，它会存储

的ArrayList，它能告诉我们的是有一个
列表
，其中有两个扩展
纸张
类型的对象（
list我通常自己创建json，而不需要第三方库。这只是因为json不需要任何头。为什么要为每个需要序列化的对象编写自定义序列化程序呢？如果有记录良好、经过测试且广泛部署的库可以为您实现这一点？@beresfordt这似乎是一种很好的方法，而且可能更好或者我。我会试试的。谢谢！
public class Comment {

    private final String text;

    public static class Builder {
        private final String text;

        public Builder(String text) {
            this.text = text;
        }

        public Comment build(){
            return new Comment(this);
        }

    }

    private Comment(Builder builder) {
        this.text = builder.text;
    }

    public String getText() {
        return text;
    }

}

public abstract class Paper {

    protected Paper(ArrayList<Comment> commentList) {
    }

}

public class WoundPaper extends Paper {

    private final String imageUri;
    private final ArrayList<Comment> commentList;

    public static class Builder {
        private final String imageUri;
        private final ArrayList<Comment> commentList;

        public Builder(String imageUri, ArrayList<Comment> commentList) {
            this.imageUri = imageUri;
            this.commentList = commentList;
        }

        public WoundPaper build() {
            return new WoundPaper(this);
        }

    }

    private WoundPaper(Builder builder) {
        super(builder.commentList);
        this.imageUri = builder.imageUri;
        this.commentList = builder.commentList;
    }

}

public abstract class Document {
    private final ArrayList<? extends Paper> paperList;


    protected Document(ArrayList<? extends Paper> paperList) {
        this.paperList = paperList;
    }

}

public class WoundDoc extends Document {

    public static class Builder {
        private final ArrayList<WoundPaper> paperList;

        public Builder(ArrayList<WoundPaper> paperList) {
            this.paperList = paperList;
        }

        public WoundDoc build() {
            return new WoundDoc(this);
        }

    }

    private WoundDoc(Builder builder) {
        super(builder.paperList);
    }

}

        Comment comment = new Comment.Builder("comment").build();
        ArrayList<Comment> commentList = new ArrayList<Comment>();
        commentList.add(comment);
        commentList.add(comment);

        WoundPaper woundPaper = new WoundPaper.Builder("some Uri", commentList).build();
        ArrayList<WoundPaper> woundPaperList = new ArrayList<WoundPaper>();
        woundPaperList.add(woundPaper);
        woundPaperList.add(woundPaper);

        WoundDoc woundDoc = new WoundDoc.Builder(woundPaperList).build();

        System.out.println("woundDoc to JSON >> " + gson.toJson(woundDoc));

public abstract class Document<T extends Paper> {
    private final ArrayList<T> paperList;


    protected Document(ArrayList<T> paperList) {
        this.paperList = paperList;
    }
}

public class WoundDoc extends Document<WoundPaper> {