When I throw exception from student name archana.
As per my understanding InvokeAll waits for all task to be completed and then return future list
Output I get is
pool-1-thread-1 Helloprerna
pool-1-thread-2 Helloabc
HELLO SOMEERROR
Execution Completed
I want other tasks output to be show for which exception is not thrown.Any suggestions
public class Executor {
public static void main(String args[]) throws InterruptedException{
ExecutorService executor=Executors.newFixedThreadPool(5);
ArrayList<Student> list = new ArrayList<Student>();
list.add(new Student("prerna"));
list.add(new Student("abc"));
list.add(new Student("archana"));
list.add(new Student("def"));
list.add(new Student("xyz"));
list.add(new Student("ritu"));
list.add(new Student("babita"));
try {
List<Future<String>> resultList=executor.invokeAll(list);
for(Future<String> f:resultList){
//if(f.isDone()){
System.out.println(f.get());
//}
}
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}catch (ExecutionException e) {
// TODO Auto-generated catch block
System.out.println("HELLO SOME ERROR");
//e.printStackTrace();
}
executor.shutdown();
executor.awaitTermination(10, TimeUnit.SECONDS);
System.out.println("Execution Completed");
}
}
.
public class Student implements Callable<String>{
String name;
public Student(String name) {
super();
this.name = name;
}
#Override
public String call() throws Exception {
// TODO Auto-generated method stub
if(name=="archana"){
throw new Exception();
}
return display(name);
}
private String display(String name2) {
try {
// System.out.println(Thread.currentThread().getName());
name2=Thread.currentThread().getName()+" Hello"+ name;
Thread.sleep(1000);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return name2;
}
}
You can move around the try/catch:
Original:
try {
List<Future<String>> resultList=executor.invokeAll(list);
for(Future<String> f:resultList){
// if(f.isDone()){
System.out.println(f.get());
//}
}
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}catch (ExecutionException e) {
// TODO Auto-generated catch block
System.out.println("HELLO SOME ERROR");
// e.printStackTrace();
}
will be rather:
try {
List<Future<String>> resultList=executor.invokeAll(list);
for(Future<String> f:resultList){
try{
System.out.println(f.get());
}catch (ExecutionException e) {
System.out.println("HELLO SOME ERROR: " + e.getMessage());
}
} catch (InterruptedException e) {
e.printStackTrace();
}
So here you will get all OK results and you can handle the exceptional execution for each task.
The pattern for this should be: Main thread create and call slaves threads, which should return ok value or error value (if there was any error). Then Main thread should collect results from slaves and process them.
Related
I am working on a multi threaded application where i get some request from JMS, threads are running to receive the message. Here how my thread is working:
Model mapper in the try block is causing the issue i think:
patientAdder.addPatient(patientAddMessage, authResult, queueSender, baseUrl, modelMapper);
here is complete code:
Executors.newSingleThreadExecutor().execute(new Runnable() {
public void run() {
while (true) {
SonicQueueMessageSender queueSender = null;
try {
queueSender = new SonicQueueMessageSender(queueConnProvider);
} catch (JMSException e3) {
// TODO Auto-generated catch block
e3.printStackTrace();
}
String patientAddMessage = null;
try {
patientAddMessage = new SonicMessageReceiver(connectionProvider)
.getAddJsonMessage("MirthMessage");
} catch (JMSException e2) {
// TODO Auto-generated catch block
e2.printStackTrace();
}
final AuthModel auth = new AuthModel();
String authResult = null;
final PatientAdder patientAdder = new PatientAdder();
SecurityTokenModel securityToken = null;
String authPostString = null;
try {
authPostString = new ObjectMapper()
.writeValueAsString(auth);
} catch (JsonGenerationException e) {
e.printStackTrace();
} catch (JsonMappingException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
System.out.println("Auth post string is: "+ authPostString);
System.out.println("base url is: " + baseUrl);
String authPostOutput = client
.doGetAuthRestPost(authPostString, url);
try {
securityToken = getAuth(authPostOutput);
} catch (JsonParseException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
} catch (JsonMappingException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
} catch (IOException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
}
authResult = securityToken.getAccessToken();
try {
patientAdder.addPatient(patientAddMessage, authResult, queueSender, baseUrl, modelMapper);
} catch (JsonParseException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (JsonMappingException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
// poster.postMessage(patientAddMessage, authResult);
catch (IllegalAccessException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (InvocationTargetException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (NoSuchMethodException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}catch(Exception e){
e.printStackTrace();
}
}
}
});
I need to map the message i'm getting in request to a bean class and for that i'm creating a ModelMapper class object that has a function to map properties but when i try to create new object of my mapper class i'm getting a NPE:
Exception in thread "pool-1-thread-1" java.lang.NullPointerException
at com.prnreferral.util.commons.ModelMapper.mapCanonicalMessageToPatientModel(ModelMapper.java:82)
at com.prnreferral.patientprocess.add.PatientAdder.addPatient(PatientAdder.java:52)
at com.prnreferral.patientprocess.add.PIXSAddPatient$1.run(PIXSAddPatient.java:148)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603)
at java.lang.Thread.run(Thread.java:722)
I'm sure that object is created as i checked it by adding some conditions, but there is something that i'm missing causing this issue
I also tried to add a new function to check if there is any issue with this function, but getting
Exception in thread "pool-1-thread-1" java.lang.NoSuchMethodError: com.prnreferral.util.commons.ModelMapper.printString()V
at com.prnreferral.patientprocess.add.PatientAdder.addPatient(PatientAdder.java:49)
at com.prnreferral.patientprocess.add.PIXSAddPatient$2.run(PIXSAddPatient.java:173)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603)
at java.lang.Thread.run(Thread.java:722)
I'm stuck on this issue, no idea what to do, can anyone help me. Thanks in advance.
I'm trying to parse json (steam webchat) which looks like that (I've changed response cause I don't wanna show the data):
/**/({
"pollid": 00,
"messages": [
{
"type": "personastate",
"timestamp": 0000000000,
"utc_timestamp": 000000000,
"steamid_from": "000000000000",
"status_flags": 0000000,
"persona_state": 0,
"persona_name": "asd"
}
]
,
"messagelast": 00,
"timestamp": 0000000000,
"utc_timestamp": 000000000000,
"messagebase": 00,
"sectimeout": 0,
"error": "OK"
})
And my parsing class looks like that:
package jsonRequest;
import java.io.IOException;
import com.fasterxml.jackson.core.JsonFactory;
import com.fasterxml.jackson.core.JsonParseException;
import com.fasterxml.jackson.core.JsonParser;
import com.fasterxml.jackson.core.JsonToken;
public class NewMessageJson {
public Integer poollid;
private String lastMessageId;
private String error;
private String messageBase;
public NewMessageJson(String response) {
response = response.substring(response.indexOf("{"),
response.indexOf("}") + 1); // cut off comment block
JsonFactory factory = new JsonFactory();
JsonParser jp = null;
try {
jp = factory.createJsonParser(response);
} catch (JsonParseException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
} catch (IOException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
}
try {
if (jp.nextToken() != JsonToken.START_OBJECT) {
throw new IOException("Server didn't return any data");
}
while (jp.nextToken() != JsonToken.END_OBJECT) {
String fieldName = jp.getCurrentName();
jp.nextToken();
if (fieldName.equals("messagelast")) {
setLastMessageId(jp.getText());
} else if (fieldName.equals("pollid")) {
setPoollid(jp.getIntValue());
} else if (fieldName.equals("messagebase")) {
setMessageBase(jp.getText());
} else if (fieldName.equals("error")) {
setError(jp.getText());
}
}
jp.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (NullPointerException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
try {
jp.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
public Integer getPoollid() {
return poollid;
}
public void setPoollid(Integer poollid) {
this.poollid = poollid;
}
public String getLastMessageId() {
return lastMessageId;
}
public void setLastMessageId(String lastMessageId) {
this.lastMessageId = lastMessageId;
}
public String getError() {
return error;
}
public void setError(String error) {
this.error = error;
}
public String getMessageBase() {
return messageBase;
}
public void setMessageBase(String messageBase) {
this.messageBase = messageBase;
}
}
And when it comes to the line
if (fieldName.equals("messagelast")) {
It crashes and returns NPE.
I have 3 other classes looking exactly like this one and everything works perfectly.
I am pretty sure the reason you are getting the NPE is because you initially instantiate JsonParser jp as null. You assign it to factory.createJsonParser(response) in your try block but do not deal with the error in any way besides printing the stack trace. If there was an error executing factory.createJsonParser(response), you need to make sure nothing else runs.
I would suggest changing your code to this:
...
JsonFactory factory = new JsonFactory();
JsonParser jp = null;
try {
jp = factory.createJsonParser(response);
} catch (JsonParseException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
System.out.println("There was an error while setting jp to factory.createJsonParser(response). Error message is: " + e1.getMessage());
} catch (IOException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
System.out.println("There was an error while setting jp to factory.createJsonParser(response). Error message is: " + e1.getMessage());
}
if(jp != null) {
try {
if (jp.nextToken() != JsonToken.START_OBJECT) {
throw new IOException("Server didn't return any data");
}
while (jp.nextToken() != JsonToken.END_OBJECT) {
String fieldName = jp.getCurrentName();
jp.nextToken();
if (fieldName.equals("messagelast")) {
setLastMessageId(jp.getText());
} else if (fieldName.equals("pollid")) {
setPoollid(jp.getIntValue());
} else if (fieldName.equals("messagebase")) {
setMessageBase(jp.getText());
} else if (fieldName.equals("error")) {
setError(jp.getText());
}
}
jp.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (NullPointerException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
try {
jp.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
...
This way, you can avoid all NPEs!
EDIT: You should also implement what peeskillet suggested
Here is my code:
private void synCampaign() {
List<Campaign> campaigns;
try {
campaigns = AdwordsCampaign.getAllCampaign();
for(Campaign c : campaigns)
CampaignDao.save(c);
} catch (ApiException e) {
try {
Thread.sleep(5000);
} catch (InterruptedException e1) {
e1.printStackTrace();
}
synCampaign();
e.printStackTrace();
} catch (RemoteException e) {
try {
Thread.sleep(5000);
} catch (InterruptedException e1) {
e1.printStackTrace();
}
synCampaign();
e.printStackTrace();
}
}
AdwordsCampaign.getAllCampaign() tries to get some remote resource. This may throw a RemoteException because the internet connection times out. When the exception is caught, I just want the thread to sleep for a while, then try to get the remote resource again.
Is there a problem with my code? Or is there a better way?
Nothing really wrong, but the (potentially infinite) retry loop with recursion (and the stack growing) makes me a little nervous. I'd write instead:
private void synCampaignWithRetries(int ntries, int msecsRetry) {
while(ntries-- >=0 ) {
try {
synCampaign();
return; // no exception? success
}
catch (ApiException e ) {
// log exception?
}
catch (RemoteException e ) {
// log exception?
}
try {
Thread.sleep(msecsRetry);
} catch (InterruptedException e1) {
// log exception?
}
}
// no success , even with ntries - log?
}
private void synCampaign() throws ApiException ,RemoteException {
List<Campaign> campaigns = AdwordsCampaign.getAllCampaign();
for(Campaign c : campaigns)
CampaignDao.save(c);
}
This looks OK except the repetition of code in catch block(be sure of number of retries you want). You may want to create a private method to handle your exception as below:
private void synCampaign() {
List<Campaign> campaigns;
try {
campaigns = AdwordsCampaign.getAllCampaign();
for(Campaign c : campaigns)
CampaignDao.save(c);
} catch (ApiException e) {
e.printStackTrace();
waitAndSync();
} catch (RemoteException e) {
e.printStackTrace();
waitAndSync();
}
}
private void waitAndSync(){
try {
Thread.sleep(5000);
} catch (InterruptedException e1) {
e1.printStackTrace();
}
synCampaign();
}
You indeed cannot catch it as a SocketTimeoutException. What is possible is to catch the RemoteException, retrieve it's cause and check if that's an instanceof SocketTimeoutException.
try{
// Your code that throws SocketTimeoutException
}catch (RemoteException e) {
if(e.getCause().getClass().equals(SocketTimeoutException.class)){
System.out.println("It is SocketTimeoutException");
// Do handling for socket exception
}else{
throw e;
}
}catch (Exception e) {
// Handling other exception. If necessary
}
I'm trying to make a new thread for parsing xml from an rss feed. When I click run it says there are errors please correct them etc. I have 2 classes in my project. The other class has no errors and this class below has only warnings that a lot of the things in the try/catch statements may be uninitialized. I understand that and figured I should still be able to run the program anyways, I expect them to be initialized and if they're not that's fine I want to know about it. Is this really what's going on or am I missing something? I thought it would compile if something may be uninitialized but its not certainly uninitialized.
public class RssParse extends Thread {
Thread th=new Thread() {
public void run(){
System.out.println("1");
URL iotd;
try {
iotd = new URL("http://www.nasa.gov/rss/image_of_the_day.rss");
} catch (MalformedURLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
System.out.println("2");
BufferedReader in;
try {
in = new BufferedReader(new InputStreamReader(iotd.openStream()));
} catch (IOException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
}
System.out.println("3");
XmlPullParserFactory factory;
try {
factory = XmlPullParserFactory.newInstance();
} catch (XmlPullParserException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
factory.setNamespaceAware(true);
System.out.println("4");
XmlPullParser xpp;
try {
xpp = factory.newPullParser();
} catch (XmlPullParserException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
System.out.println("5");
try {
xpp.setInput(in);
} catch (XmlPullParserException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
System.out.println("6");
int eventType;
try {
eventType = xpp.getEventType();
} catch (XmlPullParserException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
System.out.println(eventType+"!!!!!!!!!!!!!!!!");
while(eventType!=XmlPullParser.END_DOCUMENT){
if(eventType==XmlPullParser.START_DOCUMENT){
System.out.println("start");
}
}
try {
in.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}//method
};//thread
}//class
Look at this try/catch block for example :
URL iotd;
try {
iotd = new URL("http://www.nasa.gov/rss/image_of_the_day.rss");
} catch (MalformedURLException e) {
e.printStackTrace();
}
If iotd = new URL("...") fails, iotd will remain uninitialized.
There are two ways to deal with this :
Assign a default value to iotd, like : URL iotd = null; However, it's bad here because if you use iotd later its value may be null and can throw a NullPointerException.
Stop the execution of your function if something failed instead of just printing the stack trace. For example you can add a return statement in the catch block :
URL iotd;
try {
iotd = new URL("http://www.nasa.gov/rss/image_of_the_day.rss");
} catch (MalformedURLException e) {
e.printStackTrace();
return;
}
All the warnings you are getting are because all your catch blocks are not dealing with the exception at all (just printing the stacktrace to standard out).
Let's see it through an example:
URL iotd;
try {
iotd = new URL("http://www.nasa.gov/rss/image_of_the_day.rss");
} catch (MalformedURLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
at that snipped you are declaring a iotd variable as a URL but without initializing it (not assigning any value), you do it inside the try block - which isn't wrong by the way. However if for any reason the statement inside the try block throws an exception program flow will go to the catch block leaving the iotd variable with its initial value (unassigned).
So, in that case, execution of the program will continue and when reaching this statement:
in = new BufferedReader(new InputStreamReader(iotd.openStream()));
it will find no value assigned to the iotd variable.
To remove the warning regarding the uninitialized value you can either assign a null value to the variable when declaring it or rethrow another exception inside the catch block, stopping the program flow.
In the other hand, the snippet you posted here is not just one class, it's actually two as you are extending the Thread class and then creating an anonymous one inside its body. Using threads is easier than that in Java, just implement the Runnable interface and then instantiate a new thread from that interface:
public class MyRunnable implements Runnable {
public void run() {
// do stuff
}
}
and then:
new Thread(new MyRunnable()).start();
cheers
you need to initialize the variables above the try catch block, or give them a value in catch or finally block
find updated code here
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.MalformedURLException;
import java.net.URL;
import org.xmlpull.v1.XmlPullParser;
import org.xmlpull.v1.XmlPullParserException;
import org.xmlpull.v1.XmlPullParserFactory;
public class RssParse extends Thread {
Thread th=new Thread() {
public void run(){
System.out.println("1");
URL iotd=null;
try {
iotd = new URL("http://www.nasa.gov/rss/image_of_the_day.rss");
} catch (MalformedURLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
System.out.println("2");
BufferedReader in=null;
try {
in = new BufferedReader(new InputStreamReader(iotd.openStream()));
} catch (IOException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
}
System.out.println("3");
XmlPullParserFactory factory=null;
try {
factory = XmlPullParserFactory.newInstance();
} catch (XmlPullParserException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
factory.setNamespaceAware(true);
System.out.println("4");
XmlPullParser xpp=null;
try {
xpp = factory.newPullParser();
} catch (XmlPullParserException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
System.out.println("5");
try {
xpp.setInput(in);
} catch (XmlPullParserException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
System.out.println("6");
int eventType=-1; // set to a default value of your choice
try {
eventType = xpp.getEventType();
} catch (XmlPullParserException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
System.out.println(eventType+"!!!!!!!!!!!!!!!!");
while(eventType!=XmlPullParser.END_DOCUMENT){
if(eventType==XmlPullParser.START_DOCUMENT){
System.out.println("start");
}
}
try {
in.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}//method
};//thread
}//class
I have code which needs to do something like this
There is a list of classes each with some method (lets say execute()). I need to invoke that method on each class and there is a fixed timeOut for each invocation. Now, one of the class's execute method is badly written and results in a timeout due to which the jvm does not exit. I am running the class like this.
java ExecutorServiceTest execute TestClass1 TestClass2 TestClass3
Why does the jvm not exit after completing the execution of the code?
I get the following output
In class 1
In Class 2
java.util.concurrent.TimeoutException
at java.util.concurrent.FutureTask$Sync.innerGet(Unknown Source)
at java.util.concurrent.FutureTask.get(Unknown Source)
at ExecutorServiceTest.main(ExecutorServiceTest.java:78)
java.util.concurrent.TimeoutException
at java.util.concurrent.FutureTask$Sync.innerGet(Unknown Source)
at java.util.concurrent.FutureTask.get(Unknown Source)
The second class's execute times out and after that, the third class's execute also times out. Why does the third class's execute time out?
The jvm does not exit after the execution is complete. What is the reason? Also why is the TestClass3 execute timedout?
import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
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;
class Task implements Callable<String> {
Object instance;
Method m;
Object[] input;
Task(Object instance, Method m, Object[] input) {
this.instance = instance;
this.m = m;
this.input = input;
}
public String call() {
String s = "initial";
try {
m.invoke(instance, input);
}
catch (RuntimeException e) {
}
catch (Exception e) {
}
finally {
}
return s;
}
}
public class ExecutorServiceTest {
public static void main(String[] args) {
String methodName = args[0];
String className;
List<Object> instanceList = new ArrayList<Object>();
for (int i=1;i<args.length;i++) {
className = args[i];
Object o = null;
try {
o = Class.forName(className).newInstance();
} catch (InstantiationException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IllegalAccessException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (ClassNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
instanceList.add(o);
}
ExecutorService executor = Executors.newSingleThreadExecutor();
Iterator<Object> iter = instanceList.iterator();
while (iter.hasNext()) {
Object o = iter.next();
Method m = null;
try {
m = o.getClass().getDeclaredMethod(methodName, new Class[] {});
} catch (SecurityException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (NoSuchMethodException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
Task t = new Task(o,m,new Object[]{});
Future<String> fut = executor.submit(t);
try {
fut.get(2,TimeUnit.SECONDS);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (ExecutionException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (TimeoutException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
executor.shutdown();
}
}
public class TestClass1 {
public void execute() {
System.out.println("In class 1");
}
}
public class TestClass2 {
public void execute() {
System.out.println("In class 2");
boolean b = true;
while (b) {
}
}
}
public class TestClass3 {
public void execute() {
System.out.println("In class 3");
}
}
ExecutorService.shutdown() doesn't actually stop any running executors/threads, it just tells the service to stop accepting new tasks:
void shutdown()
Initiates an orderly shutdown in which previously submitted tasks are executed, but no new tasks will be accepted. Invocation has no additional effect if already shut down.
Your TestClass2 instance is never going to stop running because it has a while(true) loop which is never halted.
If you want to stop the ExecutorService immediately, you can use awaitTermination(long timeout, TimeUnit unit) or shutdownNow().
You need to call executor.shutdown() or create a daemon thread (using appropriate ThreadFactory passed to Executors.newSingleThreadExecutor()