如何使用jackson创建类似下面示例的json数组。
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
以下是我提供的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<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.
}
提出以下更接近的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<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 0 :(得分：45)
您需要JsonNodeFactory：
final JsonNodeFactory factory = JsonNodeFactory.instance;
此类包含创建ArrayNode，ObjectNode，IntNode，DecimalNode，TextNode和其他内容的方法。 ArrayNode和ObjectNode具有方便变异方法，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程序（ObjectWriter）又是反序列化程序（ObjectReader）。
答案 1 :(得分：13)
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。以下是将该对象转换为json字符串的方法：
//1. Convert Java object to JSON format
ObjectMapper mapper = new ObjectMapper();
String jsonString = mapper.writeValueAsString(yourObject);
有关完整的jackson-databind javadoc，请参阅here。
答案 2 :(得分：10)
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);
答案 3 :(得分：8)
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：打印使用node.toString()。