/*
* Copyright (C) 2007 The Guava Authors
*
* 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 com.google.common.base;
import static com.google.common.base.Preconditions.checkNotNull;
import com.google.common.annotations.Beta;
import java.io.PrintWriter;
import java.io.StringWriter;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import javax.annotation.Nullable;
/**
* Static utility methods pertaining to instances of {@link Throwable}.
*
* <p>See the Guava User Guide entry on <a href=
* "http://code.google.com/p/guava-libraries/wiki/ThrowablesExplained">
* Throwables</a>.
*
* @author Kevin Bourrillion
* @author Ben Yu
* @since 1.0
*/
public final class Throwables {
private Throwables() {}
/**
* Propagates {@code throwable} exactly as-is, if and only if it is an
* instance of {@code declaredType}. Example usage:
* <pre>
* try {
* someMethodThatCouldThrowAnything();
* } catch (IKnowWhatToDoWithThisException e) {
* handle(e);
* } catch (Throwable t) {
* Throwables.propagateIfInstanceOf(t, IOException.class);
* Throwables.propagateIfInstanceOf(t, SQLException.class);
* throw Throwables.propagate(t);
* }
* </pre>
*/
public static <X extends Throwable> void propagateIfInstanceOf(
@Nullable Throwable throwable, Class<X> declaredType) throws X {
// Check for null is needed to avoid frequent JNI calls to isInstance().
if (throwable != null && declaredType.isInstance(throwable)) {
throw declaredType.cast(throwable);
}
}
/**
* Propagates {@code throwable} exactly as-is, if and only if it is an
* instance of {@link RuntimeException} or {@link Error}. Example usage:
* <pre>
* try {
* someMethodThatCouldThrowAnything();
* } catch (IKnowWhatToDoWithThisException e) {
* handle(e);
* } catch (Throwable t) {
* Throwables.propagateIfPossible(t);
* throw new RuntimeException("unexpected", t);
* }
* </pre>
*/
public static void propagateIfPossible(@Nullable Throwable throwable) {
propagateIfInstanceOf(throwable, Error.class);
propagateIfInstanceOf(throwable, RuntimeException.class);
}
/**
* Propagates {@code throwable} exactly as-is, if and only if it is an
* instance of {@link RuntimeException}, {@link Error}, or
* {@code declaredType}. Example usage:
* <pre>
* try {
* someMethodThatCouldThrowAnything();
* } catch (IKnowWhatToDoWithThisException e) {
* handle(e);
* } catch (Throwable t) {
* Throwables.propagateIfPossible(t, OtherException.class);
* throw new RuntimeException("unexpected", t);
* }
* </pre>
*
* @param throwable the Throwable to possibly propagate
* @param declaredType the single checked exception type declared by the
* calling method
*/
public static <X extends Throwable> void propagateIfPossible(
@Nullable Throwable throwable, Class<X> declaredType) throws X {
propagateIfInstanceOf(throwable, declaredType);
propagateIfPossible(throwable);
}
/**
* Propagates {@code throwable} exactly as-is, if and only if it is an
* instance of {@link RuntimeException}, {@link Error}, {@code declaredType1},
* or {@code declaredType2}. In the unlikely case that you have three or more
* declared checked exception types, you can handle them all by invoking these
* methods repeatedly. See usage example in {@link
* #propagateIfPossible(Throwable, Class)}.
*
* @param throwable the Throwable to possibly propagate
* @param declaredType1 any checked exception type declared by the calling
* method
* @param declaredType2 any other checked exception type declared by the
* calling method
*/
public static <X1 extends Throwable, X2 extends Throwable>
void propagateIfPossible(@Nullable Throwable throwable,
Class<X1> declaredType1, Class<X2> declaredType2) throws X1, X2 {
checkNotNull(declaredType2);
propagateIfInstanceOf(throwable, declaredType1);
propagateIfPossible(throwable, declaredType2);
}
/**
* Propagates {@code throwable} as-is if it is an instance of
* {@link RuntimeException} or {@link Error}, or else as a last resort, wraps
* it in a {@code RuntimeException} then propagates.
* <p>
* This method always throws an exception. The {@code RuntimeException} return
* type is only for client code to make Java type system happy in case a
* return value is required by the enclosing method. Example usage:
* <pre>
* T doSomething() {
* try {
* return someMethodThatCouldThrowAnything();
* } catch (IKnowWhatToDoWithThisException e) {
* return handle(e);
* } catch (Throwable t) {
* throw Throwables.propagate(t);
* }
* }
* </pre>
*
* @param throwable the Throwable to propagate
* @return nothing will ever be returned; this return type is only for your
* convenience, as illustrated in the example above
*/
public static RuntimeException propagate(Throwable throwable) {
propagateIfPossible(checkNotNull(throwable));
throw new RuntimeException(throwable);
}
/**
* Returns the innermost cause of {@code throwable}. The first throwable in a
* chain provides context from when the error or exception was initially
* detected. Example usage:
* <pre>
* assertEquals("Unable to assign a customer id",
* Throwables.getRootCause(e).getMessage());
* </pre>
*/
public static Throwable getRootCause(Throwable throwable) {
Throwable cause;
while ((cause = throwable.getCause()) != null) {
throwable = cause;
}
return throwable;
}
/**
* Gets a {@code Throwable} cause chain as a list. The first entry in the
* list will be {@code throwable} followed by its cause hierarchy. Note
* that this is a snapshot of the cause chain and will not reflect
* any subsequent changes to the cause chain.
*
* <p>Here's an example of how it can be used to find specific types
* of exceptions in the cause chain:
*
* <pre>
* Iterables.filter(Throwables.getCausalChain(e), IOException.class));
* </pre>
*
* @param throwable the non-null {@code Throwable} to extract causes from
* @return an unmodifiable list containing the cause chain starting with
* {@code throwable}
*/
@Beta // TODO(kevinb): decide best return type
public static List<Throwable> getCausalChain(Throwable throwable) {
checkNotNull(throwable);
List<Throwable> causes = new ArrayList<Throwable>(4);
while (throwable != null) {
causes.add(throwable);
throwable = throwable.getCause();
}
return Collections.unmodifiableList(causes);
}
/**
* Returns a string containing the result of
* {@link Throwable#toString() toString()}, followed by the full, recursive
* stack trace of {@code throwable}. Note that you probably should not be
* parsing the resulting string; if you need programmatic access to the stack
* frames, you can call {@link Throwable#getStackTrace()}.
*/
public static String getStackTraceAsString(Throwable throwable) {
StringWriter stringWriter = new StringWriter();
throwable.printStackTrace(new PrintWriter(stringWriter));
return stringWriter.toString();
}
}