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Android MVVM architecture and observing changes on data from an API

I'm new to the Android MVVM architecture. I have an API running locally with data ("deals") in it. I'd like to simply make a request to the API and display that data in a text field. Currently the data does not show up when the fragment is first loaded, but if I go to another activity and then back to the fragment it loads.
There are 3 classes of importance here.
DashboardViewModel.java:
package com.example.android_client.ui.dashboard;
import androidx.lifecycle.LiveData;
import androidx.lifecycle.MutableLiveData;
import androidx.lifecycle.ViewModel;
import com.example.android_client.models.Deal;
import com.example.android_client.repository.Repository;
import java.util.List;
public class DashboardViewModel extends ViewModel {
private MutableLiveData<String> mText;
private Repository repository;
private MutableLiveData<List<Deal>> deals = null;
public void init() {
if(this.deals == null) {
this.repository = Repository.getInstance();
this.deals = this.repository.getDeals();
}
}
public DashboardViewModel() {
this.mText = new MutableLiveData<>();
}
public LiveData<List<Deal>> getDeals() {
return this.deals;
}
}
DashboardFragment.java:
package com.example.android_client.ui.dashboard;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
import androidx.annotation.NonNull;
import androidx.fragment.app.Fragment;
import androidx.lifecycle.Observer;
import androidx.lifecycle.ViewModelProviders;
import com.example.android_client.R;
import com.example.android_client.models.Deal;
import java.util.List;
public class DashboardFragment extends Fragment {
private DashboardViewModel dashboardViewModel;
public View onCreateView(#NonNull LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View root = inflater.inflate(R.layout.fragment_dashboard, container, false);
final TextView textView = root.findViewById(R.id.text_dashboard);
dashboardViewModel = ViewModelProviders.of(this).get(DashboardViewModel.class);
dashboardViewModel.init();
dashboardViewModel.getDeals().observe(this, new Observer<List<Deal>>() {
#Override
public void onChanged(List<Deal> deals) {
if (deals != null && !deals.isEmpty()) {
System.out.println(deals.get(0).toString());
textView.setText(deals.get(0).toString());
}
}
});
return root;
}
}
and Repository.java:
package com.example.android_client.repository;
import androidx.lifecycle.MutableLiveData;
import com.example.android_client.models.Deal;
import com.google.gson.Gson;
import org.jetbrains.annotations.NotNull;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import okhttp3.Call;
import okhttp3.Callback;
import okhttp3.OkHttpClient;
import okhttp3.Request;
import okhttp3.Response;
import okhttp3.ResponseBody;
public class Repository {
private static Repository instance;
private ArrayList<Deal> dealsList = new ArrayList<>();
private final OkHttpClient client = new OkHttpClient();
public static Repository getInstance() {
if(instance == null) {
instance = new Repository();
}
return instance;
}
private Repository() {}
public MutableLiveData<List<Deal>> getDeals() {
setDeals();
MutableLiveData<List<Deal>> deals = new MutableLiveData<>();
deals.setValue(dealsList);
return deals;
}
private void setDeals() {
Request request = new Request.Builder()
.url("http://10.0.2.2:8000/api/deals?<params here>")
.build();
client.newCall(request).enqueue(new Callback() {
#Override
public void onFailure(#NotNull Call call, #NotNull IOException e) {
e.printStackTrace();
}
#Override
public void onResponse(#NotNull Call call, #NotNull Response response) throws IOException {
try (ResponseBody responseBody = response.body()) {
if (!response.isSuccessful()) {
throw new IOException("Unexpected code " + response);
}
String jsonDeals = responseBody.string(); // can only call string() once or you'll get an IllegalStateException
Deal[] deals = new Gson().fromJson(jsonDeals, Deal[].class);
dealsList = new ArrayList<>(Arrays.asList(deals));
}
}
});
}
}
When stepping through the code in the Repository class I can see that setDeals() is called when I load the fragment, and the request in the callback is queued. The first time getDeals() returns, it returns a list of 0 deals (within the MutableLiveData object).
onResponse in the callback doesn't run until the fragment is already loaded. When debugging I can see that the data is in the objects (all the Gson stuff works fine), but onChanged doesn't get called again (which sets the text view).
Am I not observing changes on the deals properly?

Your code is not working due to a new live data instance be created whenever getDeals() is called and the api response value be informed to other live data instance. You must set api response value to same instance of MutableLiveData returned by getDeals()
I'm not saying that it is the best architectural solution, but if you create a mutable live data as a class attribute and return it whenever getDeals() is called. Probably, it's going to work.
Also, a good practice is return a LiveData and not a MutableLiveData to not allowing a external component modify the internal value.
Please, take a look at the piece of code below.
OBS: Maybe, there is some syntax error, because I have not compiled it
import com.example.android_client.models.Deal;
import com.google.gson.Gson;
import org.jetbrains.annotations.NotNull;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import okhttp3.Call;
import okhttp3.Callback;
import okhttp3.OkHttpClient;
import okhttp3.Request;
import okhttp3.Response;
import okhttp3.ResponseBody;
public class Repository {
private static Repository instance;
private ArrayList<Deal> dealsList = new ArrayList<>();
private final OkHttpClient client = new OkHttpClient();
private MutableLiveData<List<Deal>> _deals = new MutableLiveData<>();
private LiveData<List<Deal>> deals = _deals
public static Repository getInstance() {
if(instance == null) {
instance = new Repository();
}
return instance;
}
private Repository() {}
public LiveData<List<Deal>> getDeals() {
setDeals();
return deals;
}
private void setDeals() {
Request request = new Request.Builder()
.url("http://10.0.2.2:8000/api/deals?<params here>")
.build();
client.newCall(request).enqueue(new Callback() {
#Override
public void onFailure(#NotNull Call call, #NotNull IOException e) {
e.printStackTrace();
}
#Override
public void onResponse(#NotNull Call call, #NotNull Response response) throws IOException {
try (ResponseBody responseBody = response.body()) {
if (!response.isSuccessful()) {
throw new IOException("Unexpected code " + response);
}
String jsonDeals = responseBody.string(); // can only call string() once or you'll get an IllegalStateException
Deal[] deals = new Gson().fromJson(jsonDeals, Deal[].class);
dealsList = new ArrayList<>(Arrays.asList(deals));
_deals.setValue(dealsList);
}
}
});
}
}
When

I think this would help. Try postValue on MutableLiveData in onResponse of network call. Please change your repository class like below:
package com.example.android_client.repository;
import androidx.lifecycle.MutableLiveData;
import com.example.android_client.models.Deal;
import com.google.gson.Gson;
import org.jetbrains.annotations.NotNull;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import okhttp3.Call;
import okhttp3.Callback;
import okhttp3.OkHttpClient;
import okhttp3.Request;
import okhttp3.Response;
import okhttp3.ResponseBody;
public class Repository {
private static Repository instance;
private ArrayList<Deal> dealsList = new ArrayList<>();
private final OkHttpClient client = new OkHttpClient();
MutableLiveData<List<Deal>> deals = new MutableLiveData<>();
public static Repository getInstance() {
if(instance == null) {
instance = new Repository();
}
return instance;
}
private Repository() {}
private MutableLiveData<List<Deal>> getDeals() {
Request request = new Request.Builder()
.url("http://10.0.2.2:8000/api/deals?<params here>")
.build();
client.newCall(request).enqueue(new Callback() {
#Override
public void onFailure(#NotNull Call call, #NotNull IOException e) {
e.printStackTrace();
}
#Override
public void onResponse(#NotNull Call call, #NotNull Response response) throws IOException {
try (ResponseBody responseBody = response.body()) {
if (!response.isSuccessful()) {
throw new IOException("Unexpected code " + response);
}
String jsonDeals = responseBody.string(); // can only call string() once or you'll get an IllegalStateException
Deal[] deals = new Gson().fromJson(jsonDeals, Deal[].class);
dealsList = new ArrayList<>(Arrays.asList(deals));
deals.postValue(dealsList);
}
}
});
return deals;
}
}

in your repository class in function get deals. you are initializing live data. requesting url in background thread and posting value on live data which is not received from server yet.
to solve this create livedata instance in constructor of repository and postvalue on livedata in onResponse callback.
//sorry for bad writting, posted from mobile.

rxjava2 for load testing inconsistencies as result of onComplete event

There is code that is supposed to do the load testing form some function that performs the http call (we call it callInit here) and collects some data in the LoaTestMetricsData:
the collected responses
and the total duration of the execution.
import io.reactivex.Observable;
import io.reactivex.Scheduler;
import io.reactivex.Single;
import io.reactivex.observers.TestObserver;
import io.reactivex.schedulers.Schedulers;
import io.reactivex.subjects.PublishSubject;
import io.reactivex.subjects.Subject;
import io.restassured.internal.RestAssuredResponseImpl;
import io.restassured.response.Response;
import org.junit.jupiter.api.Test;
import java.time.Duration;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.function.Supplier;
import static java.lang.Thread.sleep;
import static org.hamcrest.CoreMatchers.equalTo;
import static org.hamcrest.CoreMatchers.is;
import static org.hamcrest.MatcherAssert.assertThat;
import static org.hamcrest.Matchers.allOf;
import static org.hamcrest.Matchers.greaterThanOrEqualTo;
import static org.hamcrest.Matchers.lessThan;
public class TestRx {
#Test
public void loadTest() {
int CALL_N_TIMES = 10;
final long CALL_NIT_EVERY_MILLISECONDS = 100;
final LoaTestMetricsData loaTestMetricsData = loadTestHttpCall(
this::callInit,
CALL_N_TIMES,
CALL_NIT_EVERY_MILLISECONDS
);
assertThat(loaTestMetricsData.responseList.size(), is(equalTo(Long.valueOf(CALL_N_TIMES).intValue())));
long errorCount = loaTestMetricsData.responseList.stream().filter(x -> x.getStatusCode() != 200).count();
long executionTime = loaTestMetricsData.duration.getSeconds();
//assertThat(errorCount, is(equalTo(0)));
assertThat(executionTime , allOf(greaterThanOrEqualTo(1L),lessThan(3L)));
}
// --
private Single<Response> callInit() {
try {
return Single.fromCallable(() -> {
System.out.println("...");
sleep(1000);
Response response = new RestAssuredResponseImpl();
return response;
});
} catch (Exception ex) {
throw new RuntimeException(ex.getMessage());
}
}
// --
private LoaTestMetricsData loadTestHttpCall(final Supplier<Single<Response>> restCallFunction, long callnTimes, long callEveryMilisseconds) {
long startTimeMillis = System.currentTimeMillis();
final LoaTestMetricsData loaDestMetricsData = new LoaTestMetricsData();
final AtomicInteger atomicInteger = new AtomicInteger(0);
final TestObserver<Response> testObserver = new TestObserver<Response>() {
public void onNext(Response response) {
loaDestMetricsData.responseList.add(response);
super.onNext(response);
}
public void onComplete() {
loaDestMetricsData.duration = Duration.ofMillis(System.currentTimeMillis() - startTimeMillis);
super.onComplete();
}
};
final Subject<Response> subjectInitCallResults = PublishSubject.create(); // Memo: Subjects are hot so if you don't observe them the right time, you may not get events. Thus: subscribe first then emit (onNext)
final Scheduler schedulerIo = Schedulers.io();
subjectInitCallResults
.subscribeOn(schedulerIo)
.subscribe(testObserver); // subscribe first
final Observable<Long> source = Observable.interval(callEveryMilisseconds, TimeUnit.MILLISECONDS).take(callnTimes);
source.subscribe(x -> {
final Single<Response> singleResult = restCallFunction.get();
singleResult
.subscribeOn(schedulerIo)
.subscribe( result -> {
int count = atomicInteger.incrementAndGet();
if(count == callnTimes) {
subjectInitCallResults.onNext(result); // then emit
subjectInitCallResults.onComplete();
} else {
subjectInitCallResults.onNext(result);
}
});
});
testObserver.awaitTerminalEvent();
testObserver.assertComplete();
testObserver.assertValueCount(Long.valueOf(callnTimes).intValue()); // !!!
return loaDestMetricsData;
}
}
The: LoaTestMetricsData is defined as:
public class LoaTestMetricsData {
public List<Response> responseList = new ArrayList<>();
public Duration duration;
}
Sometimes test fails with this error:
java.lang.AssertionError: Value counts differ; expected: 10 but was: 9 (latch = 0, values = 9, errors = 0, completions = 1)
Expected :10
Actual :9 (latch = 0, values = 9, errors = 0, completions = 1)
<Click to see difference>
If someone could tell me why?
As is some of the subjectInitCallResults.onNext() has not been executed, or consumed. But why.. I understand that PublishSubject is hot observable, thus I subscribe for the events before emitting/onNext anything to it.
UPDATE:
What would fix it, is this ugly code, that would wait for the subject to fill up:
while(subjectInitCallResults.count().blockingGet() != callnTimes) {
Thread.sleep(100);
}
..
testObserver.awaitTerminalEvent();
But is the proper / better way of doing it?
Thanks.

Validate each filed against multiple constraints using CSV Parser

I am working on a requirement where I need to parse CSV record fields against multiple validations. I am using supercsv which has support for field level processors to validate data.
My requirement is to validate each record/row field against multiple validations and save them to the database with success/failure status. for failure records I have to display all the failed validations using some codes.
Super CSV is working file but it is checking only first validation for a filed and if it is failed , ignoring second validation for the same field.Please look at below code and help me on this.
package com.demo.supercsv;
import java.io.FileReader;
import java.io.IOException;
import java.io.StringWriter;
import java.util.ArrayList;
import java.util.List;
import org.supercsv.cellprocessor.Optional;
import org.supercsv.cellprocessor.constraint.NotNull;
import org.supercsv.cellprocessor.constraint.StrMinMax;
import org.supercsv.cellprocessor.constraint.StrRegEx;
import org.supercsv.cellprocessor.constraint.UniqueHashCode;
import org.supercsv.cellprocessor.ift.CellProcessor;
import org.supercsv.exception.SuperCsvCellProcessorException;
import org.supercsv.io.CsvBeanReader;
import org.supercsv.io.CsvBeanWriter;
import org.supercsv.io.ICsvBeanReader;
import org.supercsv.io.ICsvBeanWriter;
import org.supercsv.prefs.CsvPreference;
public class ParserDemo {
public static void main(String[] args) throws IOException {
List<Employee> emps = readCSVToBean();
System.out.println(emps);
System.out.println("******");
writeCSVData(emps);
}
private static void writeCSVData(List<Employee> emps) throws IOException {
ICsvBeanWriter beanWriter = null;
StringWriter writer = new StringWriter();
try{
beanWriter = new CsvBeanWriter(writer, CsvPreference.STANDARD_PREFERENCE);
final String[] header = new String[]{"id","name","role","salary"};
final CellProcessor[] processors = getProcessors();
// write the header
beanWriter.writeHeader(header);
//write the beans data
for(Employee emp : emps){
beanWriter.write(emp, header, processors);
}
}finally{
if( beanWriter != null ) {
beanWriter.close();
}
}
System.out.println("CSV Data\n"+writer.toString());
}
private static List<Employee> readCSVToBean() throws IOException {
ICsvBeanReader beanReader = null;
List<Employee> emps = new ArrayList<Employee>();
try {
beanReader = new CsvBeanReader(new FileReader("src/employees.csv"),
CsvPreference.STANDARD_PREFERENCE);
// the name mapping provide the basis for bean setters
final String[] nameMapping = new String[]{"id","name","role","salary"};
//just read the header, so that it don't get mapped to Employee object
final String[] header = beanReader.getHeader(true);
final CellProcessor[] processors = getProcessors();
Employee emp;
while ((emp = beanReader.read(Employee.class, nameMapping,
processors)) != null) {
emps.add(emp);
if (!CaptureExceptions.SUPPRESSED_EXCEPTIONS.isEmpty()) {
System.out.println("Suppressed exceptions for row "
+ beanReader.getRowNumber() + ":");
for (SuperCsvCellProcessorException e :
CaptureExceptions.SUPPRESSED_EXCEPTIONS) {
System.out.println(e);
}
// for processing next row clearing validation list
CaptureExceptions.SUPPRESSED_EXCEPTIONS.clear();
}
}
} finally {
if (beanReader != null) {
beanReader.close();
}
}
return emps;
}
private static CellProcessor[] getProcessors() {
final CellProcessor[] processors = new CellProcessor[] {
new CaptureExceptions(new NotNull(new StrRegEx("\\d+",new StrMinMax(0, 2)))),//id must be in digits and should not be more than two charecters
new CaptureExceptions(new Optional()),
new CaptureExceptions(new Optional()),
new CaptureExceptions(new NotNull()),
// Salary
};
return processors;
}
}
Exception Handler:
package com.demo.supercsv;
import java.util.ArrayList;
import java.util.List;
import org.supercsv.cellprocessor.CellProcessorAdaptor;
import org.supercsv.cellprocessor.ift.CellProcessor;
import org.supercsv.exception.SuperCsvCellProcessorException;
import org.supercsv.util.CsvContext;
public class CaptureExceptions extends CellProcessorAdaptor {
public static List<SuperCsvCellProcessorException> SUPPRESSED_EXCEPTIONS =
new ArrayList<SuperCsvCellProcessorException>();
public CaptureExceptions(CellProcessor next) {
super(next);
}
public Object execute(Object value, CsvContext context) {
try {
return next.execute(value, context);
} catch (SuperCsvCellProcessorException e) {
// save the exception
SUPPRESSED_EXCEPTIONS.add(e);
if(value!=null)
return value.toString();
else
return "";
}
}
}
sample csv file
ID,Name,Role,Salary
a123,kiran,CEO,"5000USD"
2,Kumar,Manager,2000USD
3,David,developer,1000USD
when I run my program supercsv exception handler displaying this message for the ID value in the first row
Suppressed exceptions for row 2:
org.supercsv.exception.SuperCsvConstraintViolationException: 'a123' does not match the regular expression '\d+'
processor=org.supercsv.cellprocessor.constraint.StrRegEx
context={lineNo=2, rowNo=2, columnNo=1, rowSource=[a123, kiran, CEO, 5000USD]}
[com.demo.supercsv.Employee#23bf011e, com.demo.supercsv.Employee#50e26ae7, com.demo.supercsv.Employee#40d88d2d]
for field Id length should not be null and more than two and it should be neumeric...I have defined field processor like this.
new CaptureExceptions(new NotNull(new StrRegEx("\\d+",new StrMinMax(0, 2))))
but super csv ignoring second validation (maxlenght 2) if given input is not neumeric...if my input is 100 then its validating max lenght..but how to get two validations for wrong input.plese help me on this

SuperCSV cell processors will work in sequence. So, if it passes the previous constraint validation then it will check next one.
To achieve your goal, you need to write a custom CellProcessor, which will check whether the input is a number (digit) and length is between 0 to 2.
So, that both of those checks are done in a single step.

Unable to Cast the List Values into Comparable Value for JFreeChart

I have two classes viz. ExistInsert.java and TryExist.java . The complete code for ExistInsert is given below:
package tryexist;
import java.util.ArrayList;
import java.util.List;
import org.exist.xmldb.XQueryService;
import org.jfree.chart.ChartFactory;
import org.jfree.chart.ChartFrame;
import org.jfree.chart.JFreeChart;
import org.jfree.chart.plot.PlotOrientation;
import org.jfree.data.category.DefaultCategoryDataset;
import org.xmldb.api.DatabaseManager;
import org.xmldb.api.base.Collection;
import org.xmldb.api.base.Database;
import org.xmldb.api.base.Resource;
import org.xmldb.api.base.ResourceIterator;
import org.xmldb.api.base.ResourceSet;
public class ExistInsert {
public static String URI = "xmldb:exist://localhost:8899/exist/xmlrpc";
public static String driver = "org.exist.xmldb.DatabaseImpl";
public static List mylist = new ArrayList();
public List insert_data(String xquery){
try{
Class c1 = Class.forName(driver);
Database database=(Database) c1.newInstance();
String collectionPath= "/db";
DatabaseManager.registerDatabase(database);
Collection col=DatabaseManager.getCollection(URI+collectionPath);
XQueryService service = (XQueryService) col.getService("XQueryService","1.0");
service.setProperty("indent", "yes");
ResourceSet result = service.query(xquery);
ResourceIterator i = result.getIterator();
while(i.hasMoreResources()){
Resource r =i.nextResource();
mylist.add(((String)r.getContent()));
}
}
catch(Exception e){
System.out.println(e);
}
return mylist;
}
public void draw_bar(List values, List years ){
try{
//DefaultPieDataset data = new DefaultPieDataset();
DefaultCategoryDataset dataset = new DefaultCategoryDataset();
for(int j=0;j<values.size();j++){
dataset.addValue();
}
//JFreeChart chart = ChartFactory.createPieChart("TEST PEICHART", data, true, true, Locale.ENGLISH);
JFreeChart chart2 = ChartFactory.createLineChart("Assets", "X","Y",dataset , PlotOrientation.VERTICAL, true, true, true);
ChartFrame frame = new ChartFrame("TEST", chart2);
frame.setVisible(true);
frame.setSize(500, 500);
}
catch(Exception e){
System.out.println(e);
}
}
}
Here the function insert_data executes a xquery and return the result into list of String. The function draw_bar draws a barchart using the arguments viz values and years as list. The main problem I faced was converting the List into the Comparable, which is the requirement of dataset.addValue() . In my main program TryExist.java I have:
package tryexist;
import java.util.ArrayList;
import java.util.List;
public class Tryexist {
public static void main(String[] args) throws Exception{
ExistInsert exist = new ExistInsert();
String query = "Some query Here"
List resp = exist.insert_data(query);
List years = new ArrayList();
for (int i=2060;i<=2064;i++){
years.add(i);
}
System.out.println(years);
System.out.println(resp);
exist.draw_bar(resp,years);
}
}
Now executing query returns years and resp as [2060, 2061, 2062, 2063, 2064] and [32905657, 3091102752, 4756935449, 7954664475, 11668355950] respectively. Then How do I edit dataset.addValue() in ExistInsert.java so that I can pass above obtained values resp and years into draw_bar to make a bar diagram for the data passed.?

A complete example using DefaultCategoryDataset, BarChartDemo1, is included in the distribution and illustrated below. Click on the class name to see the source code. The example uses instances of String as column and row keys, but any Comparable can by used, as discussed here.

Validate every field in a single pass with SuperCSV

I'm trying to write a large number of rows (~2 million) from a database to a CSV file using SuperCSV. I need to perform validation on each cell as it is written, and the built-in CellProcessors do very nicely. I want to capture all the exceptions that are thrown by the CellProcessors so that I can go back to the source data and make changes.
The problem is that when there are multiple errors in a single row (e.g. The first value is out of range, the second value is null but shouldn't be), only the first CellProcessor will execute, and so I'll only see one of the errors. I want to process the whole file in a single pass, and have a complete set of exceptions at the end of it.
This is the kind of approach I'm trying:
for (Row row : rows) {
try {
csvBeanWriter.write(row, HEADER_MAPPINGS, CELL_PROCESSORS);
} catch (SuperCsvCellProcessorException e) {
log(e);
}
}
How can I achieve this? Thanks!
EDIT: Here is the code I wrote that's similar to Hound Dog's, in case it helps anyone:
import java.util.List;
import org.supercsv.cellprocessor.CellProcessorAdaptor;
import org.supercsv.cellprocessor.ift.CellProcessor;
import org.supercsv.exception.SuperCsvCellProcessorException;
import org.supercsv.util.CsvContext;
public class ExceptionCapturingCellProcessor extends CellProcessorAdaptor {
private final List<Exception> exceptions;
private final CellProcessor current;
public ExceptionCapturingCellProcessor(CellProcessor current, CellProcessor next, List<Exception> exceptions) {
super(next);
this.exceptions = exceptions;
this.current = current;
}
#Override
public Object execute(Object value, CsvContext context) {
// Check input is not null
try {
validateInputNotNull(value, context);
} catch (SuperCsvCellProcessorException e) {
exceptions.add(e);
}
// Execute wrapped CellProcessor
try {
current.execute(value, context);
} catch (SuperCsvCellProcessorException e) {
exceptions.add(e);
}
return next.execute(value, context);
}
}

I'd recommend writing a custom CellProcessor to achieve this. The following processor can be placed at the start of each CellProcessor chain - it will simply delegate to the processor chained after it, and will suppress any cell processing exceptions.
package example;
import java.util.ArrayList;
import java.util.List;
import org.supercsv.cellprocessor.CellProcessorAdaptor;
import org.supercsv.cellprocessor.ift.CellProcessor;
import org.supercsv.exception.SuperCsvCellProcessorException;
import org.supercsv.util.CsvContext;
public class SuppressException extends CellProcessorAdaptor {
public static List<SuperCsvCellProcessorException> SUPPRESSED_EXCEPTIONS =
new ArrayList<SuperCsvCellProcessorException>();
public SuppressException(CellProcessor next) {
super(next);
}
public Object execute(Object value, CsvContext context) {
try {
// attempt to execute the next processor
return next.execute(value, context);
} catch (SuperCsvCellProcessorException e) {
// save the exception
SUPPRESSED_EXCEPTIONS.add(e);
// and suppress it (null is written as "")
return null;
}
}
}
And here it is in action:
package example;
import java.io.StringWriter;
import java.util.Arrays;
import java.util.List;
import org.supercsv.cellprocessor.constraint.NotNull;
import org.supercsv.cellprocessor.constraint.StrMinMax;
import org.supercsv.cellprocessor.ift.CellProcessor;
import org.supercsv.exception.SuperCsvCellProcessorException;
import org.supercsv.io.CsvBeanWriter;
import org.supercsv.io.ICsvBeanWriter;
import org.supercsv.prefs.CsvPreference;
public class TestSuppressExceptions {
private static final CellProcessor[] PROCESSORS = {
new SuppressException(new StrMinMax(0, 4)),
new SuppressException(new NotNull()) };
private static final String[] HEADER = { "name", "age" };
public static void main(String[] args) throws Exception {
final StringWriter stringWriter = new StringWriter();
ICsvBeanWriter beanWriter = null;
try {
beanWriter = new CsvBeanWriter(stringWriter,
CsvPreference.STANDARD_PREFERENCE);
beanWriter.writeHeader(HEADER);
// set up the data
Person valid = new Person("Rick", 43);
Person nullAge = new Person("Lori", null);
Person totallyInvalid = new Person("Shane", null);
Person valid2 = new Person("Carl", 12);
List<Person> people = Arrays.asList(valid, nullAge, totallyInvalid,
valid2);
for (Person person : people) {
beanWriter.write(person, HEADER, PROCESSORS);
if (!SuppressException.SUPPRESSED_EXCEPTIONS.isEmpty()) {
System.out.println("Suppressed exceptions for row "
+ beanWriter.getRowNumber() + ":");
for (SuperCsvCellProcessorException e :
SuppressException.SUPPRESSED_EXCEPTIONS) {
System.out.println(e);
}
// clear ready for next row
SuppressException.SUPPRESSED_EXCEPTIONS.clear();
}
}
} finally {
beanWriter.close();
}
// CSV will have empty columns for invalid data
System.out.println(stringWriter);
}
}
Here's the suppressed exceptions output (row 4 has two exceptions, one for each column):
Suppressed exceptions for row 3:
org.supercsv.exception.SuperCsvConstraintViolationException: null value
encountered processor=org.supercsv.cellprocessor.constraint.NotNull
context={lineNo=3, rowNo=3, columnNo=2, rowSource=[Lori, null]}
Suppressed exceptions for row 4:
org.supercsv.exception.SuperCsvConstraintViolationException: the length (5)
of value 'Shane' does not lie between the min (0) and max (4) values (inclusive)
processor=org.supercsv.cellprocessor.constraint.StrMinMax
context={lineNo=4, rowNo=4, columnNo=2, rowSource=[Shane, null]}
org.supercsv.exception.SuperCsvConstraintViolationException: null value
encountered processor=org.supercsv.cellprocessor.constraint.NotNull
context={lineNo=4, rowNo=4, columnNo=2, rowSource=[Shane, null]}
And the CSV output
name,age
Rick,43
Lori,
,
Carl,12
Notice how the invalid values were written as "" because the SuppressException processor returned null for those values (not that you'd use the CSV output anyway, as it's not valid!).