如何创建一个json数组，就像下面使用杰克逊的例子。
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);
}
最终我将使json具有以下值。
* - (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.
}
输出以下更接近的json，但我不明白为什么在{}之前和之后有额外的引号。
{"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";
}
你需要一个JsonNodeFactory:
final JsonNodeFactory factory = JsonNodeFactory.instance;
这个类有创建ArrayNode s、ObjectNode s、IntNode s、DecimalNode s、TextNode s等的方法。 ArrayNodes和 ObjectNodes具有方便的突变方法，可以直接添加大多数JSON原语(非容器)值，而不必通过工厂(在内部，它们引用了这个工厂，这就是为什么)。
对于ObjectMapper，请注意它既是序列化器(ObjectWriter)又是反序列化器(ObjectReader)。
可以将对象写入json字符串。因此，我希望您将数据保存在根据需要定义的类的对象中。下面是将该对象转换为json字符串的方法:
//1. Convert Java object to JSON format
ObjectMapper mapper = new ObjectMapper();
String jsonString = mapper.writeValueAsString(yourObject);
查看完整的jackson-databind javadoc。
初始化JSON对象为单例实例，并构建它:
ObjectNode node = JsonNodeFactory.instance.objectNode(); // initializing
node.put("x", x); // building
PS: to println use node.toString()
您可以在不创建POJO并将其转换为JSON的情况下完成此操作。我假定您的数据在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);