I am trying to read a simple JSON response:
{
"response": "ok"
}
Here is my code:
JsonReader reader = new JsonReader(new InputStreamReader(in, "UTF-8"));
String response = null;
boolean success = false;
reader.beginObject();
if (reader.hasNext()) {
String token = reader.nextName();
if (token.equals("response")) {
response = reader.nextString();
} else {
reader.skipValue();
}
}
reader.endObject();
reader.close();
But I am getting this error:
java.lang.IllegalStateException: Expected STRING but was BEGIN_OBJECT
I don't understand what I am doing wrong.
Your parser is fine. If the code snippet you provided really belongs to the exception stack trace you're getting, then I believe that the response property of the JSON you're trying to parse has a value other than a string. For example,
{ "response": "ok" }
can be parsed by your parser just fine. However, the closest exception message you can get with your parser is a JSON similar to the one below:
{ "response": {"status": "ok"} }
that should fail with something like
Exception in thread "main" java.lang.IllegalStateException: Expected a string but was BEGIN_OBJECT at line 1 column 16 path $.response
Also note that Gson reports the problematic location at least in its latest versions (I tested it with Gson 2.5). Just make sure you're getting the expected input. If you believe the response must be in the format you mentioned, then just try to trace the input stream and find the differences. Tracing an input stream in its simplest but not the most efficient implementation, and you could have a slightly more efficient tracing reader like this:
private static Reader traceReader(final Reader reader) {
return new Reader() {
#Override
public int read(final char[] buffer, final int offset, final int length)
throws IOException {
final int read = reader.read(buffer, offset, length);
if ( read != -1 ) {
// or any other appropriate tracing output here
out.print(new String(buffer, offset, read));
out.flush();
}
return read;
}
#Override
public void close()
throws IOException {
reader.close();
}
};
}
with:
JsonReader reader = new JsonReader(traceReader(new InputStreamReader(in, "UTF-8")))
Then just re-check if you're really getting { "response": "ok" }.
Just adding this here.
In my case, I got this error because I attempted to parse an JSON object directly to an ENUM. GSON was expecting a string directly instead of a JSON object.
In my case I made a mistake modeling the reponse. My error is an object and I modeled it as a String.
Taking a closer look at my API response and modeling fixed it
The idea for solving this is something like this example:
Your JSON says that dCharg is an object, not a String:
"dCharg":{"TEXT":1000}
If it was supposed to be a String, it would have looked like:
"dCharg":"1000"
Maybe You could design like as follows
{code:java}
public class BaseEmployee{/* stuffs */}
public class RegularEmployee extends BaseEmployee{/* stuffs */}
public class Contractors extends BaseEmployee{/* stuffs */}
{code}
Related
I am working in Java using the GSON library to process a huge JSON document.
I absolutely cannot load this into memory, it is upwards of 8G and will crash the JVM with an OOM if I try to.
So I use JsonReader to process the stream of JSON.
There are certain times when I reach a BEGIN_OBJECT that want to just dump the contents of the object to string instead of processing each individual element.
For example, I am parsing something like this:
[ { "SchemaVersion":"15.0.0.0","LibraryVersion":"16.0.7324.1200","ErrorInfo":{ "ErrorMessage":"Access denied. You do not have permission to perform this action or access this resource.","ErrorValue":null,"TraceCorrelationId":"03ab459e-7076-5000-c1a7-196f1fc54384","ErrorCode":-2147024891,"ErrorTypeName":"System.UnauthorizedAccessException" },"TraceCorrelationId":"03ab459e-7076-5000-c1a7-196f1fc54384" } ]
When I get to ErrorInfo, I just want that as a string instead of parsed out. I don't want to have to parse each piece.
So here is the code:
try (InputStream is = (InputStream)response.getEntity();
InputStreamReader inputStreamReader = new InputStreamReader(is);
JsonReader jsonReader = new JsonReader(inputStreamReader)) {
if (jsonReader.peek() != JsonToken.BEGIN_ARRAY) {
return;
}
jsonReader.beginArray();
while (jsonReader.hasNext()) {
jsonReader.beginObject(); // Start of the default object on every request
jsonReader.skipValue(); // name SchemaVersion
jsonReader.skipValue(); // value
jsonReader.skipValue(); // name LibraryVersion
jsonReader.skipValue(); // value
jsonReader.skipValue(); // name ErrorInfo
if (jsonReader.peek() == JsonToken.BEGIN_OBJECT) {
// I want to dump the upcoming object to string here
...
Is it possible to dump the contents of the json reader for a given begin object until it ends to string?
Similar question, but not quite the same: Get a dump of a section (object) of JSON
Special thanks to https://stackoverflow.com/users/3389828/nikhil for the answer in the comments. You can use Gson.fromJson(jsonReader, Map.class) for this exact situation.
Gson gson = new Gson();
try (InputStream is = (InputStream)response.getEntity();
InputStreamReader inputStreamReader = new InputStreamReader(is);
JsonReader jsonReader = new JsonReader(inputStreamReader)) {
if (jsonReader.peek() != JsonToken.BEGIN_ARRAY) {
return;
}
jsonReader.beginArray();
while (jsonReader.hasNext()) {
Map header = gson.fromJson(jsonReader, Map.class);
if (header.get("ErrorInfo") != null) {
String errorDump = ((Map)header.get("ErrorInfo")).toString();
// Now I have the error dump I need but I also
// didn't load the entire thing into memory!
...
more info: https://javadeveloperzone.com/java-8/java-parse-large-json-file-gson-example/
this is my .json file:
{"Usuarios":[{"password":"admin","apellido":"Admin","correo":"Adminadmin.com","direccion":"Admin","telefono":"Admin","nombre":"Admin","username":"admin"}]}
(I tried to translate my code from Spanish to English in the comments as best I could <3)
The function that writes in the JSON is this one:
public void agregarUsuario(String nombre, String apellido, String direccion, String telefono, String correo, String username, String password) {
try {
//String jsonString = JsonObject.toString();
JSONObject usuarios = getJSONObjectFromFile("/usuarios.json");
JSONArray listaUsuario = usuarios.getJSONArray("Usuarios");
JSONObject newObject = new JSONObject();
newObject.put("nombre", nombre);
newObject.put("apellido", apellido);
newObject.put("direccion", direccion);
newObject.put("telefono", telefono);
newObject.put("correo", correo);
newObject.put("username",username);
newObject.put("password", password);
listaUsuario.put(newObject);
usuarios.put("Usuarios",listaUsuario);
ObjectOutputStream outputStream = null;
outputStream = new ObjectOutputStream(new FileOutputStream("C:\\Users\\Victor\\eclipse-workspace\\Iplane\\assets\\usuarios.json"));
outputStream.writeUTF(usuarios.toString());
outputStream.flush();
outputStream.close();
}catch(JSONException e) {
e.printStackTrace();
}catch(Exception e) {
System.err.println("Error writting json: " + e);
}
So, if in my "create user" JFrame window ,I create a new user with "asdf" as info within all the user's details, I should get the following JSON file:
{"Usuarios":[{"password":"admin","apellido":"Admin","correo":"Adminadmin.com","direccion":"Admin","telefono":"Admin","nombre":"Admin","username":"admin"},{"password":"asdf","apellido":"asdf","correo":"asdf","direccion":"asdf","telefono":"asdf","nombre":"asdf","username":"asdf"}]}
And yes! that happens! but I got also, some weird ascii/Unicode symbols in front if my JSON main object. I cant copy the output here, so this is my output on imgur: link.
Why this problem happens? how could I fix it?
If someone need my json file reader (maybe the problem is there) here you go:
public static InputStream inputStreamFromFile(String path) {
try {
InputStream inputStream = FileHandle.class.getResourceAsStream(path); //charge json in "InputStream"
return inputStream;
}catch(Exception e) {
e.printStackTrace(); //tracer for json exceptions
}
return null;
}
public static String getJsonStringFromFile(String path) {
Scanner scanner;
InputStream in = inputStreamFromFile(path); //obtains the content of the .JSON and saves it in: "in" variable
scanner = new Scanner(in); //new scanner with inputStream "in" info
String json= scanner.useDelimiter("\\Z").next(); //reads .JSON and saves it in string "json"
scanner.close(); //close the scanner
return json; //return json String
}
public static boolean objectExists (JSONObject jsonObject, String key) { //verifies whether an object exist in the json
Object o;
try {
o=jsonObject.get(key);
}catch(Exception e) {
return false;
}
return o!=null;
}
public static JSONObject getJSONObjectFromFile(String path) { //creates a jsonObject from a path
return new JSONObject(getJsonStringFromFile(path));
}
So, after writing in JSON file, I cant do anything with it, because with this weird symbols, I got errors in my json: "extraneus input: (here are the symbols) expecting [STRING, NUMBER, TRUE, FALSE, {..."
writeUTF does not write standard unicode but prepends the output with two bytes of length information
If you use writeUTF intentionally, you have to use readUTF to read the data again. Otherwise I would suggest using an OutputStreamWriter.
writeUTF()
Writes two bytes of length information to the output stream, followed
by the modified UTF-8 representation of every character in the string
s. If s is null, a NullPointerException is thrown. Each character in
the string s is converted to a group of one, two, or three bytes,
depending on the value of the character.
** Edit to clarify OutputStreamWriter:
To use the OutputStreamWriter just replace the ObjectOutputStream with OutputStreamWriter and use write instead of writeUTF.
You might find this small tutorial helpfull: Java IO: OutputStreamWriter on jenkov.com
I wrote a program that will fetch text data from http://worldtimeapi.org/api/ip.txt, and extract X, where X is the value next to "unixtime". This is what I got so far.
public class GetDataService implements DataService{
#Override
public ArrayList<String> getData() {
ArrayList<String> lines = new ArrayList<>();
try {
URL url = new URL("http://worldtimeapi.org/api/ip.txt");
BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(url.openStream()));
String line;
while ((line = bufferedReader.readLine()) != null) {
String a = line;
lines.add(a);
}
bufferedReader.close();
} catch (IOException ex) {
throw new RuntimeException("Can not making the request to the URL.");
}
return lines;
}
public interface DataService {
ArrayList<String> getData() throws IOException;
}
public class UnixTimeExtractor {
private GetDataService getDataService;
public String unixTimeExtractor() {
ArrayList<String> lines = getDataService.getData();
//how to extract the value next to "unixtime"
I don't know how to extract value next to "unixtime". And how can I test NetWork Error for GetDataService Class.
I don't know how to extract value next to "unixtime".
To extract values from a list, you can iterate over the list,
do some check on each value as needed,
and return the value when you found a match, for example:
for (String line : lines) {
if (line.startsWith("unixtime: ")) {
return line;
}
}
To extract the value that comes after "unixtime: " in a string, you could use several strategies:
line.substring("unixtime: ".length())
line.replaceAll("^unixtime: ", "")
line.split(": ")[1]
...
Btw do you really need the list of lines?
If not, then you can save memory and reduce input processing if you perform this check while reading the input stream from the URL,
and stop reading immediately after you found just what you needed.
And how can I test NetWork Error for GetDataService Class.
To test that network errors are handled correctly,
you would need to make the parts of code that can throw network errors injectable.
Then in your test cases you could inject replacement code that will throw exception,
and verify that the program handles the exceptions correctly.
One technique is "extract and extend".
That is, extract the url.openStream() call to a dedicated method:
InputStream getInputStream(URL url) throws IOException {
return url.openStream();
}
And replace in your code url.openStream() with a call to getInputStream(url).
Then in your test method, you can override this method with throwing an exception,
and verify what happens. Using fluent assertions with AssertJ:
#Test
public void test_unixtime() {
UnixTimeExtractor extractor = new UnixTimeExtractor() {
#Override
InputStream getInputStream(URL url) throws IOException {
throw new IOException();
}
};
assertThatThrownBy(extractor::unixtime)
.isInstanceOf(RuntimeException.class)
.hasMessage("Error while reading from stream");
}
You could do similarly for reading from the input stream.
You can iterate over ArrayList using indexOf and get the next value
public String unixTimeExtractor() {
List<String> lines = getDataService.getData();
int i = lines.indexOf(unixTime);
if (i != -1 && ++i < lines.size()) {
return lines.get(i);
}
return null;
}
You can use java-8 to achieve the same. Change your method to the following :
public String unixTimeExtractor() {
ArrayList<String> lines = getDataService.getData();
return lines.stream().filter(s -> s.contains("unixtime"))
.map(s -> s.substring("unixtime: ".length()))
.findFirst()
.orElse("Not found");
}
Here we stream over the list lines to check if the String unixtime is found. If it is found then we return its value using sub-string else we return Not found.
For the test case you can refer to janos' answer.
I'm using Bing's auto suggest feature to auto suggest me terms given a query. You can find the tool here: http://api.bing.com/osjson.aspx?query=pe as you can see it's returning a strange format that isn't quite JSON. Is this a specific standard different to JSON? I've attempted parsing it as JSON using...
InputStream i = new URL(url).openStream();
BufferedReader reader = new BufferedReader(new InputStreamReader(i, Charset.forName("UTF-8")));
JSONObject json = new JSONObject(readAll(reader));
but I get the error A JSONObject text must begin with '{' found:" at 2 [character 3 line 1]
readAll =
private static String readAll(Reader rd) throws IOException {
StringBuilder sb = new StringBuilder();
int cp;
while ((cp = rd.read()) != -1) {
sb.append((char) cp);
}
return sb.toString();
}
Your example is valid JSON:
["pe",["people","people search","petsmart","petco","petfinder","pep boys","people finder","people of walmart"]]
It is not object, it is array, which contains string at the first position and another array at the second. So try parse as JSONArray, not as JSONObject.
A JSON Object starts with a { and ends with a }, which a JSONObject class was designed to parse.
A JSON Array starts with a [ and ends with a ], which a JSONArray class was designed to parse.
I hope this helps.
I'm trying to get the post data in Java. Seems like it should be one of the simplest things to do right? I mean, HttpServletRequest.getParameter has to do it right? So how can you get the raw post data?
I found HttpServletRequest get JSON POST data and used Kdeveloper's code to pull the post data from a request. It works, but theres a catch: I can only get that post data once.
Heres the method I made from Kdeveloper's code:
public static String getPostData(HttpServletRequest req) {
StringBuilder sb = new StringBuilder();
try {
BufferedReader reader = req.getReader();
reader.mark(10000);
String line;
do {
line = reader.readLine();
sb.append(line).append("\n");
} while (line != null);
reader.reset();
// do NOT close the reader here, or you won't be able to get the post data twice
} catch(IOException e) {
logger.warn("getPostData couldn't.. get the post data", e); // This has happened if the request's reader is closed
}
return sb.toString();
}
Previously I had closed the reader at the end of this method, but that caused exceptions when the method ran more than once on the same request. Without closing it, no exceptions happen, but the method returns an empty string.
Honestly, there should just be an exposed req.getPostData() method - did no one think that would be useful?
So how can I write this method such that it always returns the correct post data?
The request body is available as byte stream by HttpServletRequest#getInputStream():
InputStream body = request.getInputStream();
// ...
Or as character stream by HttpServletRequest#getReader():
Reader body = request.getReader();
// ...
Note that you can read it only once. The client ain't going to resend the same request multiple times. Calling getParameter() and so on will implicitly also read it. If you need to break down parameters later on, you've got to store the body somewhere and process yourself.
We had a situation where IE forced us to post as text/plain, so we had to manually parse the parameters using getReader. The servlet was being used for long polling, so when AsyncContext::dispatch was executed after a delay, it was literally reposting the request empty handed.
So I just stored the post in the request when it first appeared by using HttpServletRequest::setAttribute. The getReader method empties the buffer, where getParameter empties the buffer too but stores the parameters automagically.
String input = null;
// we have to store the string, which can only be read one time, because when the
// servlet awakens an AsyncContext, it reposts the request and returns here empty handed
if ((input = (String) request.getAttribute("com.xp.input")) == null) {
StringBuilder buffer = new StringBuilder();
BufferedReader reader = request.getReader();
String line;
while((line = reader.readLine()) != null){
buffer.append(line);
}
// reqBytes = buffer.toString().getBytes();
input = buffer.toString();
request.setAttribute("com.xp.input", input);
}
if (input == null) {
response.setContentType("text/plain");
PrintWriter out = response.getWriter();
out.print("{\"act\":\"fail\",\"msg\":\"invalid\"}");
}
This worked for me: (notice that java 8 is required)
String requestData = request.getReader().lines().collect(Collectors.joining());
UserJsonParser u = gson.fromJson(requestData, UserJsonParser.class);
UserJsonParse is a class that shows gson how to parse the json formant.
class is like that:
public class UserJsonParser {
private String username;
private String name;
private String lastname;
private String mail;
private String pass1;
//then put setters and getters
}
the json string that is parsed is like that:
$jsonData: { "username": "testuser", "pass1": "clave1234" }
The rest of values (mail, lastname, name) are set to null