使用 jackson 创建 json 对象

json hashmap java jackson

2022-09-01 08:00:48

如何使用 jackson 创建一个 json 数组，如下面的示例所示。

我尝试使用ObjectMapper，但这似乎不正确。

      try (DirectoryStream<Path> ds = Files.newDirectoryStream(path)) {
            for (Path file : ds) {
                System.out.println("name:"+file.getFileName()+
                        "\n"+
                        "mime:"+Files.probeContentType(file)+
                "\n"+
                "locked:"+!Files.isWritable(file));
            }
        } catch (IOException e) {
            System.err.println(e);
        }

最终，我将制作一个具有以下值的json。

 * - (int)    size    file size in b. required
 * - (int)    ts      file modification time in unix time. required
 * - (string) mime    mimetype. required for folders, others - optionally
 * - (bool)   read    read permissions. required
 * - (bool)   write   write permissions. required
 * - (bool)   locked  is object locked. optionally
 * - (bool)   hidden  is object hidden. optionally
 * - (string) alias   for symlinks - link target path relative to root path. optionally
 * - (string) target  for symlinks - link target path. optionally

下面是我提供的一个示例 json。

"files": [
    {
        "mime": "directory",
        "ts": 1334071677,
        "read": 1,
        "write": 0,
        "size": 0,
        "hash": "l1_Lw",
        "volumeid": "l1_",
        "name": "Demo",
        "locked": 1,
        "dirs": 1
    },
    {
        "mime": "directory",
        "ts": 1334071677,
        "read": 1,
        "write": 0,
        "size": 0,
        "hash": "l1_Lw",
        "volumeid": "l1_",
        "name": "Demo",
        "locked": 1,
        "dirs": 1
    },
    {
        "mime": "directory",
        "ts": 1340114567,
        "read": 0,
        "write": 0,
        "size": 0,
        "hash": "l1_QmFja3Vw",
        "name": "Backup",
        "phash": "l1_Lw",
        "locked": 1
    },
    {
        "mime": "directory",
        "ts": 1310252178,
        "read": 1,
        "write": 0,
        "size": 0,
        "hash": "l1_SW1hZ2Vz",
        "name": "Images",
        "phash": "l1_Lw",
        "locked": 1
    },
    {
        "mime": "application\/x-genesis-rom",
        "ts": 1310347586,
        "read": 1,
        "write": 0,
        "size": 3683,
        "hash": "l1_UkVBRE1FLm1k",
        "name": "README.md",
        "phash": "l1_Lw",
        "locked": 1
    }
]

编辑 1

        Map<String, Object> filesMap = new HashMap<>();
        List<Object> files = new ArrayList<Object>();
        System.out.println("\nNo filter applied:");
        try (DirectoryStream<Path> ds = Files.newDirectoryStream(path)) {
            for (Path file : ds) {
                Map<String, Object> fileInfo = new HashMap<>();
                fileInfo.put("name", file.getFileName().toString());
//                Prints Files in Director
//                Files.getAttribute(file,"size");
                System.out.println("name:" + file.getFileName().toString() +
                        "\n" +
                        "mime:" + Files.probeContentType(file) +
                        "\n" +
                        "locked:" + !Files.isWritable(file));
                ObjectMapper mapper = new ObjectMapper();
                String json = mapper.writeValueAsString(fileInfo);
                files.add(json);
            }
        } catch (IOException e) {
            System.err.println(e);
        }
        files.toArray();
        filesMap.put("files", files);
        ObjectMapper mapper = new ObjectMapper();
        String jsonString;
        try {
            jsonString = mapper.writeValueAsString(filesMap);
        } catch (IOException e) {
            jsonString = "fail";  //To change body of catch statement use File | Settings | File Templates.
        }

放出以下更接近的json，但我无法弄清楚为什么在{}之前和之后都有额外的引号。

{"files":["{\"name\":\"32C92124-EFCF-42C1-AFD2-8B741AE6854B.jpg\"}","{\"name\":\"58D5B83F-4065-4D6E-92BE-8181D99CB6CB.jpg\"}","{\"name\":\"7B1464A0-FBA1-429E-8A39-3DE5B539FBF8.jpg\"}","{\"name\":\"888159CF-45BE-475F-8C6A-64B3E1D97278.jpg\"}"]}

最终答案

    Map<String, Object> filesMap = new HashMap<>();
    List<Object> files = new ArrayList<Object>();
    System.out.println("\nNo filter applied:");
    try (DirectoryStream<Path> ds = Files.newDirectoryStream(path)) {
        for (Path file : ds) {
            Map<String, Object> fileInfo = new HashMap<>();
            fileInfo.put("name", file.getFileName().toString());
            System.out.println("name:" + file.getFileName().toString() +
                    "\n" +
                    "mime:" + Files.probeContentType(file) +
                    "\n" +
                    "locked:" + !Files.isWritable(file));
            files.add(fileInfo);
        }
    } catch (IOException e) {
        System.err.println(e);
    }
    files.toArray();
    filesMap.put("files", files);
    ObjectMapper mapper = new ObjectMapper();
    String jsonString;
    try {
        jsonString = mapper.writeValueAsString(filesMap);
    } catch (IOException e) {
        jsonString = "fail"; 
    }

答案 1

你需要一个JsonNodeFactory：

final JsonNodeFactory factory = JsonNodeFactory.instance;

此类具有创建 s、s、s、s、s 等的方法。s 和 s 具有方便的突变方法，可以直接添加大多数 JSON 基元（非容器）值，而无需通过工厂（好吧，在内部，它们引用此工厂，这就是为什么）。ArrayNodeObjectNodeIntNodeDecimalNodeTextNodeArrayNodeObjectNode

至于，请注意它既是序列化程序（）又是反序列化程序（）。ObjectMapperObjectWriterObjectReader

答案 2

您可以将对象写入 json 字符串。因此，我希望您将数据放在根据需要定义的类的对象中。下面介绍如何将该对象转换为 json 字符串：

//1. Convert Java object to JSON format
ObjectMapper mapper = new ObjectMapper();

String jsonString = mapper.writeValueAsString(yourObject);

请参阅此处，了解完整的 jackson-databind javadoc。