Develop Reference

Why onGuildMemberRoleAdd doesnt work? DiscordBot in Java

The "onGuildMemberRoleAdd" listener just doesn't work ... As if the listener was ignored...
And I don't know why :( can someone help me pls!
I also implemented the listener in the main class.
Listener:
package listener.rollen;
import net.dv8tion.jda.api.events.guild.member.GuildMemberRoleAddEvent;
import net.dv8tion.jda.api.hooks.ListenerAdapter;
public class RollenAdd extends ListenerAdapter {
#Override
public void onGuildMemberRoleAdd(GuildMemberRoleAddEvent event) {
System.out.println("test");
}
}
Main
package main;
import listener.*;
import listener.punktesystem.SprachchatConnect;
import listener.punktesystem.SprachchatDisconnect;
import listener.rollen.*;
import net.dv8tion.jda.api.OnlineStatus;
import net.dv8tion.jda.api.entities.Activity;
import net.dv8tion.jda.api.sharding.DefaultShardManagerBuilder;
import net.dv8tion.jda.api.sharding.ShardManager;
import javax.security.auth.login.LoginException;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
public class Start {
public static Start INSTANCE;
public ShardManager shardMan;
public static void main(String[] args) {
try {
new Start();
} catch (LoginException e) {
e.printStackTrace();
}
}
public Start() throws LoginException, IllegalArgumentException {
INSTANCE = this;
DefaultShardManagerBuilder builder = DefaultShardManagerBuilder.createDefault("Token");
builder.setActivity(Activity.watching("ZZZZs Zaubertrick"));
builder.setStatus(OnlineStatus.ONLINE);
listeners(builder);
shardMan = builder.build();
shutdown();
}
public void shutdown(){
new Thread(() -> {
String line = "";
BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
try{
while ((line = reader.readLine()) != null){
if(line.equalsIgnoreCase("exit")){
if(shardMan != null){
shardMan.setStatus(OnlineStatus.OFFLINE);
shardMan.shutdown();
System.out.println("Bot ist offline!");
}
}
}
}catch (IOException e){
e.printStackTrace();
}
}).start();
}
public void listeners(DefaultShardManagerBuilder builder){
builder.addEventListeners(new RollenAdd());
}
}
I think that's all that has to do with it...
At first I thought it was because the Privileged Gateway Intents were not activated in the DiscordDeveloperPortal, but after that it still didn't work

JavaSocket Read Hangs on HTTP Call

I am building a collection program in Java that collects data from websites using their apis. I am encountering this problem where it will hang on an http call. I tried to work around it by executing an http call over an executor service with a timeout. That doesn't seem to work as it would keep timing out and retrying. I figured it might be something to do with the API so after a retry I would reinitialize a whole new object per website API. Still no solution. I am trying to identify the root cause of this but can't seem to put my finger on it.
Here is a look at my flickr manager class that handles the calls to flickr.
import java.net.SocketException;
import java.net.UnknownHostException;
import java.util.Collection;
import java.util.Collections;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;
import java.util.logging.Level;
import java.util.logging.Logger;
import org.scribe.exceptions.OAuthConnectionException;
import com.flickr4java.flickr.Flickr;
import com.flickr4java.flickr.FlickrException;
import com.flickr4java.flickr.FlickrRuntimeException;
import com.flickr4java.flickr.REST;
import com.flickr4java.flickr.RequestContext;
import com.flickr4java.flickr.auth.Auth;
import com.flickr4java.flickr.auth.Permission;
import com.flickr4java.flickr.people.User;
import com.flickr4java.flickr.photos.Exif;
import com.flickr4java.flickr.photos.Extras;
import com.flickr4java.flickr.photos.Photo;
import com.flickr4java.flickr.photos.PhotoList;
import com.flickr4java.flickr.photos.SearchParameters;
import com.flickr4java.flickr.photos.Size;
import com.google.common.util.concurrent.RateLimiter;
public class FlickrManager {
private final static Logger LOG = Logger.getLogger(FlickrManager.class.getName());
private final static ExecutorService executorService = Executors.newSingleThreadExecutor();
private Flickr flickr;
private final int MAX_PER_PAGE = 500;
private final RateLimiter rateLimiter;
private String ApiKey;
private String ApiSecret;
private String authToken;
private String authTokenSecret;
private Integer hostPort;
private String hostAddress;
private String httpScheme;
public FlickrManager(Flickr flickr, double apiCallsPerSecond) throws FlickrException {
this.flickr = flickr;
flickr.getTestInterface().echo(Collections.emptyMap());
//get flickr info to reinitialize flickr object if necessary
this.ApiKey = flickr.getApiKey();
this.ApiSecret = flickr.getSharedSecret();
this.hostPort = flickr.getTransport().getPort();
this.hostAddress = flickr.getTransport().getHost();
this.httpScheme = flickr.getTransport().getScheme();
if(flickr.getAuth() != null){
this.authToken = flickr.getAuth().getToken();
this.authTokenSecret = flickr.getAuth().getTokenSecret();
}
this.rateLimiter = RateLimiter.create(apiCallsPerSecond);
}
private void initialize(){
this.flickr = null;
REST rest = new REST(this.hostAddress,this.hostPort);
rest.setScheme(this.httpScheme);
this.flickr = new Flickr(this.ApiKey, this.ApiSecret,rest);
if(this.authToken != null && this.authTokenSecret != null){
RequestContext requestContext = RequestContext.getRequestContext();
Auth auth = new Auth();
auth.setPermission(Permission.READ);
auth.setToken(this.authToken);
auth.setTokenSecret(this.authTokenSecret);
requestContext.setAuth(auth);
flickr.setAuth(auth);
}
}
public User getUserInfo(String flickrProfileId) throws FlickrException{
return doFlickrAction(new CallableFlickrTask<User>(){
#Override
public User execute() throws FlickrException {
return flickr.getPeopleInterface().getInfo(flickrProfileId);
}
});
}
public PhotoList<Photo> search(SearchParameters params, int page) throws FlickrException{
return doFlickrAction(new CallableFlickrTask<PhotoList<Photo>>(){
#Override
public PhotoList<Photo> execute() throws FlickrException {
return flickr.getPhotosInterface().search(params, MAX_PER_PAGE, page);
}
});
}
public PhotoList<Photo> getUserPhotos(String userNSID, int page) throws FlickrException{
return doFlickrAction(new CallableFlickrTask<PhotoList<Photo>>(){
#Override
public PhotoList<Photo> execute() throws FlickrException {
return flickr.getPeopleInterface().getPhotos(
userNSID,
null, null, null, null, null,
Flickr.CONTENTTYPE_PHOTO, null,
Extras.ALL_EXTRAS, 100, page);
}
});
}
//Catch the execption inside the function for failure to get exif
public Collection<Exif> getPhotoExif(Photo photo) throws FlickrException, FlickrRuntimeException {
return doFlickrAction(new CallableFlickrTask<Collection<Exif>>(){
#Override
public Collection<Exif> execute() throws FlickrException {
return flickr.getPhotosInterface().getExif(photo.getId(),photo.getSecret());
}
});
}
public Collection<Size> getAvailablePhotoSizes(Photo photo) throws FlickrException{
return doFlickrAction(new CallableFlickrTask<Collection<Size>>(){
#Override
public Collection<Size> execute() throws FlickrException {
return flickr.getPhotosInterface().getSizes(photo.getId());
}
});
}
private abstract class CallableFlickrTask<T> {
public abstract T execute() throws FlickrException, FlickrRuntimeException;
}
private <T> T doFlickrAction(CallableFlickrTask<T> callable) throws FlickrException {
while(true){
rateLimiter.acquire();
Future<T> future = executorService.submit(new Callable<T>() {
#Override
public T call() throws Exception {
return callable.execute();
}});
try {
return future.get(5, TimeUnit.MINUTES);
} catch (InterruptedException e) {
LOG.log(Level.INFO,"Interrupted exception: {0}",e.getMessage());
initialize(); //initialize if it's been interupted
} catch (ExecutionException e) {
Throwable cause = e.getCause();
if( cause instanceof UnknownHostException ||
cause instanceof SocketException ||
cause instanceof OAuthConnectionException ){
//sleep and retry
LOG.log(Level.INFO,"Unknown Host or Socket exception. Retry: {0}",e.getMessage());
try {
Thread.sleep(10000);
initialize();
} catch (InterruptedException ex) {
LOG.log(Level.INFO, "Thread sleep was interrupted exception: {0}", ex.getMessage());
}
}
//if it's not of the above exceptions, then rethrow
else if (cause instanceof FlickrException) {
throw (FlickrException) cause;
}
else {
throw new IllegalStateException(e);
}
} catch (TimeoutException e) {
LOG.log(Level.INFO,"Timeout Exception: {0}",e.getMessage());
initialize(); //initialize again after timeout
}
}
}
}
I also used jvisualvm to get a look at what the collection is doing while it's hanging. The thread dump is here: Thread dump

Database connection suffers of concurrent threads

I've recently starting working on a java webapp (JSP / Servlet) that was developed by the internal developer of a company.
This app randomly doesn't return data, and inspecting the log I found some NullPointerExceptions related to the classes' member variable which holds the database connection. Following the stack trace it seems that a second thread closes the connection after it ended its task leaving the first thread without a connection.
By the needs of the company the app uses different databases, one which rules appdata, and others which contain data the app has to retrieve. So every class attached to the main servlet may connect to one or more databases depending on the task it has to accomplish.
I'm not familiar with JavaEE but giving a look at the database connection class, I see nothing which protect threads from conflicting each other.
Which is the correct way to handle such connections?
This is the code of the Database handler:
package it.metmi.mmasgis.utils;
import java.sql.*;
import java.util.ArrayList;
import java.util.HashMap;
import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;
public class DBManager
{
private String szDatabase;
private String szUsername;
private String szPassword;
private String szError;
private Connection db;
private boolean bConnected;
private Logger logger;
public DBManager(String szDBName)
{
this(szDBName, "", "");
}
public DBManager(String szDBName, String szName, String szPass)
{
szDatabase = szDBName;
szUsername = szName;
szPassword = szPass;
bConnected = false;
szError = "";
logger = LogManager.getFormatterLogger(DBManager.class.getName());
}
public boolean connect()
{
logger.entry();
try {
Class.forName("com.mysql.jdbc.Driver");
if(!szDatabase.isEmpty())
{
String szCon = "jdbc:mysql://localhost/" + szDatabase;
if(!szUsername.isEmpty())
{
szCon += "?user=" + szUsername;
if(!szPassword.isEmpty())
szCon += "&password=" + szPassword;
}
db = DriverManager.getConnection(szCon);
bConnected = true;
} else {
logger.error("No database name!!");
System.exit(0);
}
} catch(SQLException | ClassNotFoundException e) {
szError = e.getMessage();
e.printStackTrace();
logger.error("Can't connect: %s", e);
}
return logger.exit(bConnected);
}
public void disconnect()
{
logger.entry();
try {
db.close();
bConnected = false;
} catch(SQLException e) {
e.printStackTrace();
logger.error("Can't disconnect: %s", e);
}
logger.exit();
}
public boolean isConnected()
{
return bConnected;
}
public String getError()
{
return szError;
}
public ArrayList<HashMap<String,String>> query(String szQuery)
{
logger.entry(szQuery);
ArrayList<HashMap<String,String>> aResults = new ArrayList<HashMap<String,String>>();
int iCols = 0;
try {
Statement stmt = db.createStatement();
logger.info("Query: %s", szQuery);
ResultSet rs = stmt.executeQuery(szQuery);
ResultSetMetaData rsmd = rs.getMetaData();
iCols = rsmd.getColumnCount();
while(rs.next())
{
HashMap<String,String> pv = new HashMap<String,String>();
for(int i = 0; i < iCols; i++)
{
String szCol = rsmd.getColumnLabel(i + 1);
String szVal = rs.getString(i + 1);
pv.put(szCol, szVal);
}
aResults.add(pv);
}
rs.close();
stmt.close();
} catch(SQLException e) {
e.printStackTrace();
szError = e.getMessage();
logger.error("Error executing query: %s", e);
}
return logger.exit(aResults);
}
public boolean update(String szQuery)
{
logger.entry(szQuery);
boolean bResult = false;
try {
Statement stmt = db.createStatement();
logger.info("Query: %s", szQuery);
stmt.executeUpdate(szQuery);
bResult = true;
stmt.close();
} catch(SQLException e) {
e.printStackTrace();
szError = e.getMessage();
bResult = false;
logger.error("Error executing query: %s", e);
}
return logger.exit(bResult);
}
}
The class Task which all the servlet classes are based on, is a simple abstract class:
package it.metmi.mmasgis.servlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public abstract class Task
{
public abstract void doTask(HttpServletRequest request, HttpServletResponse response);
}
The class which throws NullPointerExceptions it this one, during the invocation of db.disconnect(). This class is called rapidly via AJAX 4 or 5 times from the interface written in JS.
package it.metmi.mmasgis.servlet.params;
import it.metmi.mmasgis.servlet.Task;
import it.metmi.mmasgis.utils.Const;
import it.metmi.mmasgis.utils.DBManager;
import it.metmi.mmasgis.utils.Query;
import it.metmi.mmasgis.utils.Utility;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.HashMap;
import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;
public class ClassType extends Task
{
private DBManager db = null;
private Logger logger = LogManager.getFormatterLogger(ClassType.class.getName());
#Override
public void doTask(HttpServletRequest request, HttpServletResponse response)
{
logger.entry(request, response);
String szCensimento = Utility.getParameter(request, "censimento");
String szCategoria = Utility.getParameter(request, "category");
ArrayList<HashMap<String,String>> aClasses = new ArrayList<HashMap<String,String>>();
PrintWriter out = null;
logger.debug("Census: %s", szCensimento);
logger.debug("Category: %s", szCategoria);
db = new DBManager(szCensimento, Const.DB_USER, Const.DB_PASS);
if(db.connect())
{
String szQuery = String.format(Query.classes, szCategoria, szCategoria);
aClasses = db.query(szQuery);
db.disconnect();
}
try {
out = response.getWriter();
jsonEncode(aClasses, out);
} catch(IOException e) {
e.printStackTrace();
logger.error("Failed to encode JSON: %s", e);
}
logger.exit();
}
private void jsonEncode(ArrayList<HashMap<String,String>> aData, PrintWriter out)
{
HashMap<String,Object> result = new HashMap<String,Object>();
result.put("results", aData);
result.put("success", true);
Gson gson = new GsonBuilder().create();
gson.toJson(result, out);
}
}
If the webapp would use only one database, it could be rewritten as a Singleton, but in this way I have no idea on how to handle different connections for different databases.
How can avoid these exceptions?

The problem was that the connection object was declared as member.
Moving the variable inside the methods resolved.

Full RESTFUL WebService with GSON and Java

I have created a RESTFUL webservice, witch returns a json, but at this time i only consult and show a simple select * , i need to create a complete CRUD solution, if anyone have some samples to share, i'll appreciate.
Best Regards to all
My code until now are:
DAO - Access.java
package dao;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import dto.Usuarios;
public class Access
{
public ArrayList<Usuarios> getUsuarios(Connection con) throws SQLException
{
ArrayList<Usuarios> usuariosList = new ArrayList<Usuarios>();
PreparedStatement stmt = con.prepareStatement("SELECT * FROM usuarios");
ResultSet rs = stmt.executeQuery();
try
{
while(rs.next())
{
Usuarios usuariosObj = new Usuarios();
usuariosObj.setUsr_id(rs.getInt("usr_id"));
usuariosObj.setUsr_login(rs.getString("usr_login"));
usuariosObj.setUsr_pwd(rs.getString("usr_pwd"));
usuariosList.add(usuariosObj);
}
} catch (SQLException e)
{
e.printStackTrace();
}
return usuariosList;
}
}
DTO - Usuarios.java
package dto;
public class Usuarios
{
private int usr_id;
private String usr_login;
private String usr_pwd;
public Usuarios()
{
}
public Usuarios(int usr_id, String usr_login, String usr_pwd)
{
super();
this.usr_id = usr_id;
this.usr_login = usr_login;
this.usr_pwd = usr_pwd;
}
public int getUsr_id()
{
return usr_id;
}
public void setUsr_id(int usr_id)
{
this.usr_id = usr_id;
}
public String getUsr_login()
{
return usr_login;
}
public void setUsr_login(String usr_login)
{
this.usr_login = usr_login;
}
public String getUsr_pwd()
{
return usr_pwd;
}
public void setUsr_pwd(String usr_pwd)
{
this.usr_pwd = usr_pwd;
}
#Override
public String toString()
{
return "[ {usr_id=" + usr_id + ", usr_login=" + usr_login + ", usr_pwd=" + usr_pwd + "} ]";
}
}
Model - AccessManager.java
package model;
import java.sql.Connection;
import java.sql.SQLException;
import java.util.ArrayList;
import dao.Access;
import dao.Database;
import dto.Usuarios;
public class AccessManager
{
public ArrayList<Usuarios> getUsuarios() throws Exception
{
ArrayList<Usuarios> usuariosList = new ArrayList<Usuarios>();
Database db = new Database();
Connection con = db.getConnection();
Access access = new Access();
usuariosList = access.getUsuarios(con);
return usuariosList;
}
}
WebService - UsuariosService.java
package webService;
import java.util.ArrayList;
import javax.ws.rs.GET;
import javax.ws.rs.Path;
import javax.ws.rs.Produces;
import com.google.gson.Gson;
import model.AccessManager;
import dto.Usuarios;
#Path("/UsuariosService")
public class UsuariosService
{
#GET
#Path("/usuarios")
#Produces("application/json")
public String usuarios()
{
String usuarios = null;
ArrayList<Usuarios> usuariosList = new ArrayList<Usuarios>();
try
{
usuariosList = new AccessManager().getUsuarios();
Gson gson = new Gson();
//usuarios = gson.toJson(usuariosList);
usuarios = "{\"usuarios\" :" + gson.toJson(usuariosList) + "}";
} catch (Exception e)
{
e.printStackTrace();
}
return usuarios;
}
}

Usually you should ask a specific trouble you have instead of ask for samples. It looks like you have a structured code and all you need is implement all operations exposing as a service.
In case you need a sample, there quite a lot of resources on the web. Something like this: https://code.google.com/p/javaee6-crud-example/
I'll try give you some quick tips below:
WebService - UsuariosService.java
#POST
#Path("/usuarios")
public Response save(Usuario user) {
try {
manager= new AccessManager();
manager.save(user);
return Response.ok("User has been created.").build();
} catch (Exception e) {
e.printStackTrace();
}
return usuarios;
}
#DELETE
#Path("/usuarios/{id}")
public Response delete(#PathParam("id") String id) {
try {
manager= new AccessManager();
manager.delete(id);
return Response.ok("User has been deleted.").build();
} catch (Exception e) {
e.printStackTrace();
}
return usuarios;
}
#PUT
#Path("/usuarios/{id}")
public Response delete(#PathParam("id") String id, Usuario user) {
try {
manager= new AccessManager();
manager.update(id, user);
return Response.ok("User has been updated.").build();
} catch (Exception e) {
e.printStackTrace();
}
return usuarios;
}
If you don´t understand the usage of PUT, DELETE, POST and so on, I recommend you to read HTTP Method Tutorial. There is several discussion regarding this but you might skip it for a while.
I think you might get an idea from here. Your DAO needs to implement methods to perform CRUD interface as well. The link I've added has a very simple sample that might help as well. You might also check this JPA link.
Not sure whether info above helped but I think it is a start since you have to code it in order to understand more about it :)

Crawling Web and Stored Links

I want to create a thread in order to crawl all links of a website and store it in LinkedHashSet, but when I print the size of this LinkedHashSet, it prints nothing. I've started learning crawling! I've referenced The Art of Java. Here is my code:
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.LinkedHashSet;
import java.util.logging.Level;
import java.util.logging.Logger;
public class TestThread {
public void crawl(URL url) {
try {
BufferedReader reader = new BufferedReader(
new InputStreamReader(url.openConnection().getInputStream()));
String line = reader.readLine();
LinkedHashSet toCrawlList = new LinkedHashSet();
while (line != null) {
toCrawlList.add(line);
System.out.println(toCrawlList.size());
}
} catch (IOException ex) {
Logger.getLogger(TestThread.class.getName()).log(Level.SEVERE, null, ex);
}
}
public static void main(String[] args) {
final TestThread test1 = new TestThread();
Thread thread = new Thread(new Runnable() {
public void run(){
try {
test1.crawl(new URL("http://stackoverflow.com/"));
} catch (MalformedURLException ex) {
Logger.getLogger(TestThread.class.getName()).log(Level.SEVERE, null, ex);
}
}
});
}
}

You should fill your list like this:
while ((line = reader.readLine()) != null) {
toCrawlList.add(line);
}
System.out.println(toCrawlList.size());
If that doesn't work, try to set a break point in your code and find out if your reader even contains anything.