src/main/java/rx/exceptions/CompositeException.java
/**
* Copyright 2014 Netflix, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package rx.exceptions;
import java.io.*;
import java.util.*;
/**
* Represents an exception that is a composite of one or more other exceptions. A {@code CompositeException}
* does not modify the structure of any exception it wraps, but at print-time it iterates through the list of
* Throwables contained in the composite in order to print them all.
*
* Its invariant is to contain an immutable, ordered (by insertion order), unique list of non-composite
* exceptions. You can retrieve individual exceptions in this list with {@link #getExceptions()}.
*
* The {@link #printStackTrace()} implementation handles the StackTrace in a customized way instead of using
* {@code getCause()} so that it can avoid circular references.
*
* If you invoke {@link #getCause()}, it will lazily create the causal chain but will stop if it finds any
* Throwable in the chain that it has already seen.
*/
public final class CompositeException extends RuntimeException {
private static final long serialVersionUID = 3026362227162912146L;
private final List<Throwable> exceptions;
private final String message;
private Throwable cause;
/**
* Constructs a CompositeException with the given prefix and error collection.
* @param messagePrefix the prefix to use (actually unused)
* @param errors the collection of errors
* @deprecated please use {@link #CompositeException(Collection)} */
@Deprecated
public CompositeException(String messagePrefix, Collection<? extends Throwable> errors) { // NOPMD
Set<Throwable> deDupedExceptions = new LinkedHashSet<Throwable>();
List<Throwable> localExceptions = new ArrayList<Throwable>();
if (errors != null) {
for (Throwable ex : errors) {
if (ex instanceof CompositeException) {
deDupedExceptions.addAll(((CompositeException) ex).getExceptions());
} else
if (ex != null) {
deDupedExceptions.add(ex);
} else {
deDupedExceptions.add(new NullPointerException());
}
}
} else {
deDupedExceptions.add(new NullPointerException());
}
localExceptions.addAll(deDupedExceptions);
this.exceptions = Collections.unmodifiableList(localExceptions);
this.message = exceptions.size() + " exceptions occurred. ";
}
/**
* Constructs a CompositeException instance with the Throwable elements
* of the supplied Collection.
* <p>Null values are replaced by {@link NullPointerException}.
* @param errors the collection of errors
*/
public CompositeException(Collection<? extends Throwable> errors) {
this(null, errors);
}
/**
* Constructs a CompositeException instance with the supplied initial Throwables.
* @param errors the array of Throwables
* @since 1.3
*/
public CompositeException(Throwable... errors) {
Set<Throwable> deDupedExceptions = new LinkedHashSet<Throwable>();
List<Throwable> localExceptions = new ArrayList<Throwable>();
if (errors != null) {
for (Throwable ex : errors) {
if (ex instanceof CompositeException) {
deDupedExceptions.addAll(((CompositeException) ex).getExceptions());
} else
if (ex != null) {
deDupedExceptions.add(ex);
} else {
deDupedExceptions.add(new NullPointerException());
}
}
} else {
deDupedExceptions.add(new NullPointerException());
}
localExceptions.addAll(deDupedExceptions);
this.exceptions = Collections.unmodifiableList(localExceptions);
this.message = exceptions.size() + " exceptions occurred. ";
}
/**
* Retrieves the list of exceptions that make up the {@code CompositeException}
*
* @return the exceptions that make up the {@code CompositeException}, as a {@link List} of {@link Throwable}s
*/
public List<Throwable> getExceptions() {
return exceptions;
}
@Override
public String getMessage() {
return message;
}
@Override
public synchronized Throwable getCause() { // NOPMD
if (cause == null) {
// we lazily generate this causal chain if this is called
CompositeExceptionCausalChain localCause = new CompositeExceptionCausalChain();
Set<Throwable> seenCauses = new HashSet<Throwable>();
Throwable chain = localCause;
for (Throwable e : exceptions) {
if (seenCauses.contains(e)) {
// already seen this outer Throwable so skip
continue;
}
seenCauses.add(e);
List<Throwable> listOfCauses = getListOfCauses(e);
// check if any of them have been seen before
for (Throwable child : listOfCauses) {
if (seenCauses.contains(child)) {
// already seen this outer Throwable so skip
e = new RuntimeException("Duplicate found in causal chain so cropping to prevent loop ...");
continue;
}
seenCauses.add(child);
}
// we now have 'e' as the last in the chain
try {
chain.initCause(e);
} catch (Throwable t) { // NOPMD
// ignore
// the javadocs say that some Throwables (depending on how they're made) will never
// let me call initCause without blowing up even if it returns null
}
chain = getRootCause(chain);
}
cause = localCause;
}
return cause;
}
/**
* All of the following {@code printStackTrace} functionality is derived from JDK {@link Throwable}
* {@code printStackTrace}. In particular, the {@code PrintStreamOrWriter} abstraction is copied wholesale.
*
* Changes from the official JDK implementation:<ul>
* <li>no infinite loop detection</li>
* <li>smaller critical section holding {@link PrintStream} lock</li>
* <li>explicit knowledge about the exceptions {@link List} that this loops through</li>
* </ul>
*/
@Override
public void printStackTrace() {
printStackTrace(System.err);
}
@Override
public void printStackTrace(PrintStream s) {
printStackTrace(new WrappedPrintStream(s));
}
@Override
public void printStackTrace(PrintWriter s) {
printStackTrace(new WrappedPrintWriter(s));
}
/**
* Special handling for printing out a {@code CompositeException}.
* Loops through all inner exceptions and prints them out.
*
* @param s
* stream to print to
*/
private void printStackTrace(PrintStreamOrWriter s) {
StringBuilder b = new StringBuilder(128);
b.append(this).append('\n');
for (StackTraceElement myStackElement : getStackTrace()) {
b.append("\tat ").append(myStackElement).append('\n');
}
int i = 1;
for (Throwable ex : exceptions) {
b.append(" ComposedException ").append(i).append(" :\n");
appendStackTrace(b, ex, "\t");
i++;
}
synchronized (s.lock()) {
s.println(b.toString());
}
}
private void appendStackTrace(StringBuilder b, Throwable ex, String prefix) {
b.append(prefix).append(ex).append('\n');
for (StackTraceElement stackElement : ex.getStackTrace()) {
b.append("\t\tat ").append(stackElement).append('\n');
}
if (ex.getCause() != null) {
b.append("\tCaused by: ");
appendStackTrace(b, ex.getCause(), "");
}
}
abstract static class PrintStreamOrWriter {
/** Returns the object to be locked when using this StreamOrWriter */
abstract Object lock();
/** Prints the specified string as a line on this StreamOrWriter */
abstract void println(Object o);
}
/**
* Same abstraction and implementation as in JDK to allow PrintStream and PrintWriter to share implementation
*/
static final class WrappedPrintStream extends PrintStreamOrWriter {
private final PrintStream printStream;
WrappedPrintStream(PrintStream printStream) {
this.printStream = printStream;
}
@Override
Object lock() {
return printStream;
}
@Override
void println(Object o) {
printStream.println(o);
}
}
static final class WrappedPrintWriter extends PrintStreamOrWriter {
private final PrintWriter printWriter;
WrappedPrintWriter(PrintWriter printWriter) {
this.printWriter = printWriter;
}
@Override
Object lock() {
return printWriter;
}
@Override
void println(Object o) {
printWriter.println(o);
}
}
/* package-private */final static class CompositeExceptionCausalChain extends RuntimeException {
private static final long serialVersionUID = 3875212506787802066L;
/* package-private */static final String MESSAGE = "Chain of Causes for CompositeException In Order Received =>";
@Override
public String getMessage() {
return MESSAGE;
}
}
private List<Throwable> getListOfCauses(Throwable ex) {
List<Throwable> list = new ArrayList<Throwable>();
Throwable root = ex.getCause();
if (root == null || root == ex) {
return list;
} else {
while (true) {
list.add(root);
Throwable cause = root.getCause();
if (cause == null || cause == root) {
return list;
} else {
root = root.getCause();
}
}
}
}
/**
* Returns the root cause of {@code e}. If {@code e.getCause()} returns {@code null} or {@code e}, just return {@code e} itself.
*
* @param e the {@link Throwable} {@code e}.
* @return The root cause of {@code e}. If {@code e.getCause()} returns {@code null} or {@code e}, just return {@code e} itself.
*/
private Throwable getRootCause(Throwable e) {
Throwable root = e.getCause();
if (root == null || root == e) {
return e;
} else {
while (true) {
Throwable cause = root.getCause();
if (cause == null || cause == root) {
return root;
}
root = root.getCause();
}
}
}
}