Java：从Json文档读取单个值

Question

我试图从mongodb查询中获取num_likes的值。

查询的代码：

FindIterable<Document> comments = postsCollection.find(eq("permalink", permalink))
.projection(fields(exclude(Arrays.asList("body","date", "author", "tags", "title")),slice("comments", ordinal, 1)));

for(Document c: comments) {
    System.out.println(c.get("comments"));
}

[Document{{author=Tonia Surace, body=Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum, email=[e-mail], num_likes=1}}]

for(Document c: comments) {
    System.out.println(c.get("comments"));
    ArrayList c2 = (ArrayList<Object>) c.get("comments");
    Document d = (Document) c2.get(0);
    System.out.println(d.get("num_likes"));
}

Answer 1

您可以使用任何Java json库来更方便地访问json字段。就像杰克逊或者格森。