This might be a dumb question but what is the simplest way to read and parse JSON from URL in Java?
In Groovy, it's a matter of few lines of code. Java examples that I find are ridiculously long (and have huge exception handling block).
All I want to do is to read the content of this link.
If you don't mind using a couple libraries it can be done in a single line.
Include Apache Commons IOUtils & json.org libraries.
JSONObject json = new JSONObject(IOUtils.toString(new URL("https://graph.facebook.com/me"), Charset.forName("UTF-8")));
It's very easy, using jersey-client, just include this maven dependency:
<dependency>
<groupId>org.glassfish.jersey.core</groupId>
<artifactId>jersey-client</artifactId>
<version>2.25.1</version>
</dependency>
Then invoke it using this example:
String json = ClientBuilder.newClient().target("http://api.coindesk.com/v1/bpi/currentprice.json").request().accept(MediaType.APPLICATION_JSON).get(String.class);
Then use Google's Gson to parse the JSON:
Gson gson = new Gson();
Type gm = new TypeToken<CoinDeskMessage>() {}.getType();
CoinDeskMessage cdm = gson.fromJson(json, gm);
The easiest way: Use gson, google's own goto json library. https://code.google.com/p/google-gson/
Here is a sample. I'm going to this free geolocator website and parsing the json and displaying my zipcode. (just put this stuff in a main method to test it out)
String sURL = "http://freegeoip.net/json/"; //just a string
// Connect to the URL using java's native library
URL url = new URL(sURL);
URLConnection request = url.openConnection();
request.connect();
// Convert to a JSON object to print data
JsonParser jp = new JsonParser(); //from gson
JsonElement root = jp.parse(new InputStreamReader((InputStream) request.getContent())); //Convert the input stream to a json element
JsonObject rootobj = root.getAsJsonObject(); //May be an array, may be an object.
String zipcode = rootobj.get("zip_code").getAsString(); //just grab the zipcode
I wanted to add an updated answer here since (somewhat) recent updates to the JDK have made it a bit easier to read the contents of an HTTP URL. Like others have said, you'll still need to use a JSON library to do the parsing, since the JDK doesn't currently contain one. Here are a few of the most commonly used JSON libraries for Java:
To retrieve JSON from a URL, this seems to be the simplest way using strictly JDK classes (but probably not something you'd want to do for large payloads), Java 9 introduced: https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/io/InputStream.html#readAllBytes()
try(java.io.InputStream is = new java.net.URL("https://graph.facebook.com/me").openStream()) {
String contents = new String(is.readAllBytes());
}
To parse the JSON using the GSON library, for example
com.google.gson.JsonElement element = com.google.gson.JsonParser.parseString(contents); //from 'com.google.code.gson:gson:2.8.6'
I have done the json parser in simplest way, here it is
package com.inzane.shoapp.activity;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.UnsupportedEncodingException;
import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.DefaultHttpClient;
import org.json.JSONException;
import org.json.JSONObject;
import android.util.Log;
public class JSONParser {
static InputStream is = null;
static JSONObject jObj = null;
static String json = "";
// constructor
public JSONParser() {
}
public JSONObject getJSONFromUrl(String url) {
// Making HTTP request
try {
// defaultHttpClient
DefaultHttpClient httpClient = new DefaultHttpClient();
HttpPost httpPost = new HttpPost(url);
HttpResponse httpResponse = httpClient.execute(httpPost);
HttpEntity httpEntity = httpResponse.getEntity();
is = httpEntity.getContent();
} catch (UnsupportedEncodingException e) {
e.printStackTrace();
} catch (ClientProtocolException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
try {
BufferedReader reader = new BufferedReader(new InputStreamReader(
is, "iso-8859-1"), 8);
StringBuilder sb = new StringBuilder();
String line = null;
while ((line = reader.readLine()) != null) {
sb.append(line + "\n");
System.out.println(line);
}
is.close();
json = sb.toString();
} catch (Exception e) {
Log.e("Buffer Error", "Error converting result " + e.toString());
}
// try parse the string to a JSON object
try {
jObj = new JSONObject(json);
} catch (JSONException e) {
Log.e("JSON Parser", "Error parsing data " + e.toString());
System.out.println("error on parse data in jsonparser.java");
}
// return JSON String
return jObj;
}
}
this class returns the json object from the url
and when you want the json object you just call this class and the method in your Activity class
my code is here
String url = "your url";
JSONParser jsonParser = new JSONParser();
JSONObject object = jsonParser.getJSONFromUrl(url);
String content=object.getString("json key");
here the "json key" is denoted that the key in your json file
this is a simple json file example
{
"json":"hi"
}
Here "json" is key and "hi" is value
This will get your json value to string content.
I am not sure if this is efficient, but this is one of the possible ways:
Read json from url use url.openStream() and read contents into a string.
construct a JSON object with this string (more at json.org)
JSONObject(java.lang.String source)
Construct a JSONObject from a source JSON text string.
Here are couple of alternatives versions with Jackson (since there are more than one ways you might want data as):
ObjectMapper mapper = new ObjectMapper(); // just need one
// Got a Java class that data maps to nicely? If so:
FacebookGraph graph = mapper.readValue(url, FaceBookGraph.class);
// Or: if no class (and don't need one), just map to Map.class:
Map<String,Object> map = mapper.readValue(url, Map.class);
And specifically the usual (IMO) case where you want to deal with Java objects, can be made one liner:
FacebookGraph graph = new ObjectMapper().readValue(url, FaceBookGraph.class);
Other libs like Gson also support one-line methods; why many examples show much longer sections is odd. And even worse is that many examples use obsolete org.json library; it may have been the first thing around, but there are half a dozen better alternatives so there is very little reason to use it.
Using the Maven artifact org.json:json I got the following code, which I think is quite short. Not as short as possible, but still usable.
package so4308554;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.Reader;
import java.net.URL;
import java.nio.charset.Charset;
import org.json.JSONException;
import org.json.JSONObject;
public class JsonReader {
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();
}
public static JSONObject readJsonFromUrl(String url) throws IOException, JSONException {
InputStream is = new URL(url).openStream();
try {
BufferedReader rd = new BufferedReader(new InputStreamReader(is, Charset.forName("UTF-8")));
String jsonText = readAll(rd);
JSONObject json = new JSONObject(jsonText);
return json;
} finally {
is.close();
}
}
public static void main(String[] args) throws IOException, JSONException {
JSONObject json = readJsonFromUrl("https://graph.facebook.com/19292868552");
System.out.println(json.toString());
System.out.println(json.get("id"));
}
}
Use HttpClient to grab the contents of the URL. And then use the library from json.org to parse the JSON. I've used these two libraries on many projects and they have been robust and simple to use.
Other than that you can try using a Facebook API java library. I don't have any experience in this area, but there is a question on stack overflow related to using a Facebook API in java. You may want to look at RestFB as a good choice for a library to use.
I have found this to be the easiest way by far.
Use this method:
public static String getJSON(String url) {
HttpsURLConnection con = null;
try {
URL u = new URL(url);
con = (HttpsURLConnection) u.openConnection();
con.connect();
BufferedReader br = new BufferedReader(new InputStreamReader(con.getInputStream()));
StringBuilder sb = new StringBuilder();
String line;
while ((line = br.readLine()) != null) {
sb.append(line + "\n");
}
br.close();
return sb.toString();
} catch (MalformedURLException ex) {
ex.printStackTrace();
} catch (IOException ex) {
ex.printStackTrace();
} finally {
if (con != null) {
try {
con.disconnect();
} catch (Exception ex) {
ex.printStackTrace();
}
}
}
return null;
}
And use it like this:
String json = getJSON(url);
JSONObject obj;
try {
obj = new JSONObject(json);
JSONArray results_arr = obj.getJSONArray("results");
final int n = results_arr.length();
for (int i = 0; i < n; ++i) {
// get the place id of each object in JSON (Google Search API)
String place_id = results_arr.getJSONObject(i).getString("place_id");
}
}
Here's a full sample of how to parse Json content. The example takes the Android versions statistics (found from Android Studio source code here, which links to here).
Copy the "distributions.json" file you get from there into res/raw, as a fallback.
build.gradle
implementation 'com.google.code.gson:gson:2.8.6'
manifest
<uses-permission android:name="android.permission.INTERNET" />
MainActivity.kt
class MainActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
if (savedInstanceState != null)
return
thread {
// https://cs.android.com/android/platform/superproject/+/studio-master-dev:tools/adt/idea/android/src/com/android/tools/idea/stats/DistributionService.java
var root: JsonArray
Log.d("AppLog", "loading...")
try {
HttpURLConnection.setFollowRedirects(true)
val statsUrl = "https://dl.google.com/android/studio/metadata/distributions.json" //just a string
val url = URL(statsUrl)
val request: HttpURLConnection = url.openConnection() as HttpURLConnection
request.connectTimeout = 3000
request.connect()
InputStreamReader(request.content as InputStream).use {
root = JsonParser.parseReader(it).asJsonArray
}
} catch (e: Exception) {
Log.d("AppLog", "error while loading from Internet, so using fallback")
e.printStackTrace()
InputStreamReader(resources.openRawResource(R.raw.distributions)).use {
root = JsonParser.parseReader(it).asJsonArray
}
}
val decimalFormat = DecimalFormat("0.00")
Log.d("AppLog", "result:")
root.forEach {
val androidVersionInfo = it.asJsonObject
val versionNickName = androidVersionInfo.get("name").asString
val versionName = androidVersionInfo.get("version").asString
val versionApiLevel = androidVersionInfo.get("apiLevel").asInt
val marketSharePercentage = androidVersionInfo.get("distributionPercentage").asFloat * 100f
Log.d("AppLog", "\"$versionNickName\" - $versionName - API$versionApiLevel - ${decimalFormat.format(marketSharePercentage)}%")
}
}
}
}
As alternative to the dependency, you can also use this instead:
InputStreamReader(request.content as InputStream).use {
val jsonArray = JSONArray(it.readText())
}
and the fallback:
InputStreamReader(resources.openRawResource(R.raw.distributions)).use {
val jsonArray = JSONArray(it.readText())
}
The result of running this:
loading...
result:
"Ice Cream Sandwich" - 4.0 - API15 - 0.20%
"Jelly Bean" - 4.1 - API16 - 0.60%
"Jelly Bean" - 4.2 - API17 - 0.80%
"Jelly Bean" - 4.3 - API18 - 0.30%
"KitKat" - 4.4 - API19 - 4.00%
"Lollipop" - 5.0 - API21 - 1.80%
"Lollipop" - 5.1 - API22 - 7.40%
"Marshmallow" - 6.0 - API23 - 11.20%
"Nougat" - 7.0 - API24 - 7.50%
"Nougat" - 7.1 - API25 - 5.40%
"Oreo" - 8.0 - API26 - 7.30%
"Oreo" - 8.1 - API27 - 14.00%
"Pie" - 9.0 - API28 - 31.30%
"Android 10" - 10.0 - API29 - 8.20%
Source: Stackoverflow.com