使用jackson创建json对象
如何使用jackson创建一个类似于下面示例的json数组。
我尝试使用ObjectMapper，但这似乎不正确。
try (DirectoryStream 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
这是我提供的json示例。
"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 filesMap = new HashMap(); List files = new ArrayList(); System.out.println("\nNo filter applied:"); try (DirectoryStream ds = Files.newDirectoryStream(path)) { for (Path file : ds) { Map 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. }
提出了以下更接近的json，但我无法弄清楚为什么{}之前和之后的额外引号。
{"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 filesMap = new HashMap(); List files = new ArrayList(); System.out.println("\nNo filter applied:"); try (DirectoryStream ds = Files.newDirectoryStream(path)) { for (Path file : ds) { Map 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"; }
你需要一个JsonNodeFactory ：
final JsonNodeFactory factory = JsonNodeFactory.instance;
该类具有创建ArrayNode ， ObjectNode ， IntNode ， DecimalNode ， TextNode和诸如此类的方法。 ArrayNode和ObjectNode具有方便的变异方法，可以直接添加大多数JSON原语（非容器）值，而无需经过工厂（在内部，它们引用此工厂，这就是原因）。
对于ObjectMapper ，请注意它既是序列化器（ ObjectWriter ）又是反序列化器（ ObjectReader ）。
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您的需要定义的类的对象中。 以下是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);
在这里查看完整的jackson-databind javadoc。
您可以在不创建POJO并将其转换为JSON的情况下执行此操作。 我假设您的数据在Record对象中。
JsonNode rootNode = mapper.createObjectNode(); ArrayNode childNodes = mapper.createArrayNode(); for (Record record : records) { JsonNode element = mapper.createObjectNode(); ((ObjectNode) element).put("mime": record.getDirectory()); //fill rest of fields which are needed similar to this. //Also here record.getDirectory() method will should return "directory" //according to your json file. childNodes.add(element); } ((ObjectNode) rootNode).put("files", childNodes);
将JSON对象初始化为单例实例，并构建它：
ObjectNode node = JsonNodeFactory.instance.objectNode(); // initializing node.put("x", x); // building
PS：println使用node.toString() 。