我有五节课:Comment
,Paper
,WoundPaper
,Document
,WoundDoc
。Comment
是文本的持有人。Paper
是空的抽象类。WoundPaper
扩展了Paper
并存储了Comments
的String和ArrayList。Document
是抽象类,存储<? extends Paper>
的ArrayList。WoundDoc
扩展了Document
。
您可以在下面看到这些类:
评论类别:
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;
}
}
论文班:
public abstract class Paper {
protected Paper(ArrayList<Comment> commentList) {
}
}
WoundPaper类:
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;
}
}
文件类别:
public abstract class Document {
private final ArrayList<? extends Paper> paperList;
protected Document(ArrayList<? extends Paper> paperList) {
this.paperList = paperList;
}
}
WoundDoc类:
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);
}
}
现在我必须创建一个
WoundDoc
实例并通过Gson将其转换为JSON字符串,这是执行此操作的示例代码: 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));
但是输出很奇怪:
将伤口文档转换为JSON >> {“paperList”:[{},{}]}
正如我之前显示的,
WoundDoc
存储WoundPaper
的列表,每个WoundPaper
存储comment
的列表,但是为什么输出中没有comment
? 最佳答案
当gson序列化WoundDoc
时,它只能说明存在两个对象类型的List
,它们扩展了Paper
(List<? extends Paper>
);具体类型未知。由于Paper
没有供gson使用的字段,因此只能说该列表中有两个条目,但是由于它们是Paper
类型,它没有字段,因此无法解决如何序列化这些对象的方法。
解决此问题的一种方法是将类型从实现中传递给抽象类,以便在gson检查它们时可以看到遇到的对象是哪个类的实例,从而确定如何序列化它们。
更新文档以使用类型参数:
public abstract class Document<T extends Paper> {
private final ArrayList<T> paperList;
protected Document(ArrayList<T> paperList) {
this.paperList = paperList;
}
}
更新WoundDoc以将类型传递给Document:
public class WoundDoc extends Document<WoundPaper> {
如果您无法进行上述更改,另一种解决方法是为
WoundDoc
编写自定义序列化程序我个人会使用第一个解决方案和通过类型,因为我很懒,编写自定义序列化程序会更费力
编辑:对jackson稍加喊叫,如果您尝试序列化某些内容,它将抛出异常,但无法解决该问题。