yoko-core/src/test/java/test/util/MultiException.java

package test.util;

import java.io.PrintStream;
import java.io.PrintWriter;
import java.io.StringWriter;
import java.util.Map;
import java.util.TreeMap;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Future;

public class MultiException extends RuntimeException {
    private static final String SEP = "--------------------------------------------------------------------------------";
    private static final String NULL_COUNT_FORMAT = SEP + "%n%d \u2715 null%n" + SEP + "%n";
    private static final String ENTRY_FORMAT = "%n" + SEP + "%n%d \u2715 %s" + SEP + "%n";
    private Map<String, Integer> map = new TreeMap<>();
    private int nullCount;

    public boolean isEmpty() {
        return map.isEmpty();
    }

    public Integer add(Throwable t) {
        if (t == null) return nullCount++;
        String desc = getDescription(t);
        Integer count = map.get(desc);
        return count == null ?
                map.put(desc, 1) :
                map.put(desc, ++count);
    }

    private String getDescription(Throwable t) {
        StringWriter sw = new StringWriter();
        PrintWriter pw = new PrintWriter(sw);
        pw.println(t);
        pw.println(SEP);
        t.printStackTrace(pw);
        pw.flush();
        return sw.getBuffer().toString();
    }

    public <T extends Throwable, F extends Future<T>> MultiException(Iterable<F> results) {
        for (F f : results)
            try {
                add(f.get());
            } catch (InterruptedException | ExecutionException e) {
                add(e);
            }
    }

    @Override
    public void printStackTrace(PrintStream s) {
        s.printf(NULL_COUNT_FORMAT, nullCount);
        for (Map.Entry<String, Integer> e : map.entrySet()) s.printf(ENTRY_FORMAT, e.getValue(), e.getKey());
    }

    @Override
    public void printStackTrace(PrintWriter s) {
        s.printf(NULL_COUNT_FORMAT, nullCount);
        for (Map.Entry<String, Integer> e : map.entrySet()) s.printf(ENTRY_FORMAT, e.getValue(), e.getKey());
    }
}