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/*
* 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 static java.util.Arrays.asList;
import static java.util.Collections.unmodifiableList;
import com.google.common.annotations.Beta;
import com.google.common.annotations.VisibleForTesting;
import java.io.PrintWriter;
import java.io.StringWriter;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.AbstractList;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import javax.annotation.CheckReturnValue;
import javax.annotation.Nullable;
/**
* Static utility methods pertaining to instances of {@link Throwable}.
*
* See the Guava User Guide entry on Throwables.
*
* @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:
*
* try {
* someMethodThatCouldThrowAnything();
* } catch (IKnowWhatToDoWithThisException e) {
* handle(e);
* } catch (Throwable t) {
* Throwables.propagateIfInstanceOf(t, IOException.class);
* Throwables.propagateIfInstanceOf(t, SQLException.class);
* throw Throwables.propagate(t);
* }
*
*/
public static void propagateIfInstanceOf(
@Nullable Throwable throwable, Class 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:
*
* try {
* someMethodThatCouldThrowAnything();
* } catch (IKnowWhatToDoWithThisException e) {
* handle(e);
* } catch (Throwable t) {
* Throwables.propagateIfPossible(t);
* throw new RuntimeException("unexpected", t);
* }
*
*/
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:
*
* try {
* someMethodThatCouldThrowAnything();
* } catch (IKnowWhatToDoWithThisException e) {
* handle(e);
* } catch (Throwable t) {
* Throwables.propagateIfPossible(t, OtherException.class);
* throw new RuntimeException("unexpected", t);
* }
*
*
* @param throwable the Throwable to possibly propagate
* @param declaredType the single checked exception type declared by the calling method
*/
public static void propagateIfPossible(
@Nullable Throwable throwable, Class 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 void propagateIfPossible(
@Nullable Throwable throwable, Class declaredType1, Class 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} and then propagates.
*
* 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:
*
* T doSomething() {
* try {
* return someMethodThatCouldThrowAnything();
* } catch (IKnowWhatToDoWithThisException e) {
* return handle(e);
* } catch (Throwable t) {
* throw Throwables.propagate(t);
* }
* }
*
*
* @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:
*
* assertEquals("Unable to assign a customer id", Throwables.getRootCause(e).getMessage());
*
*/
@CheckReturnValue
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.
*
* Here's an example of how it can be used to find specific types of exceptions in the cause
* chain:
*
*
* Iterables.filter(Throwables.getCausalChain(e), IOException.class));
*
*
* @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
@CheckReturnValue
public static List getCausalChain(Throwable throwable) {
checkNotNull(throwable);
List causes = new ArrayList(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()}.
*/
@CheckReturnValue
public static String getStackTraceAsString(Throwable throwable) {
StringWriter stringWriter = new StringWriter();
throwable.printStackTrace(new PrintWriter(stringWriter));
return stringWriter.toString();
}
/**
* Returns the stack trace of {@code throwable}, possibly providing slower iteration over the full
* trace but faster iteration over parts of the trace. Here, "slower" and "faster" are defined in
* comparison to the normal way to access the stack trace, {@link Throwable#getStackTrace()
* throwable.getStackTrace()}. Note, however, that this method's special implementation is not
* available for all platforms and configurations. If that implementation is unavailable, this
* method falls back to {@code getStackTrace}. Callers that require the special implementation can
* check its availability with {@link #lazyStackTraceIsLazy()}.
*
* The expected (but not guaranteed) performance of the special implementation differs from
* {@code getStackTrace} in one main way: The {@code lazyStackTrace} call itself returns quickly
* by delaying the per-stack-frame work until each element is accessed. Roughly speaking:
*
*
* - {@code getStackTrace} takes {@code stackSize} time to return but then negligible time to
* retrieve each element of the returned list.
*
- {@code lazyStackTrace} takes negligible time to return but then {@code 1/stackSize} time to
* retrieve each element of the returned list (probably slightly more than {@code 1/stackSize}).
*
*
* Note: The special implementation does not respect calls to {@link Throwable#setStackTrace
* throwable.setStackTrace}. Instead, it always reflects the original stack trace from the
* exception's creation.
*
* @since 19.0
*/
// TODO(cpovirk): Say something about the possibility that List access could fail at runtime?
@Beta
@CheckReturnValue
public static List lazyStackTrace(Throwable throwable) {
return lazyStackTraceIsLazy()
? jlaStackTrace(throwable)
: unmodifiableList(asList(throwable.getStackTrace()));
}
/**
* Returns whether {@link #lazyStackTrace} will use the special implementation described in its
* documentation.
*
* @since 19.0
*/
@Beta
@CheckReturnValue
public static boolean lazyStackTraceIsLazy() {
return getStackTraceElementMethod != null & getStackTraceDepthMethod != null;
}
private static List jlaStackTrace(final Throwable t) {
checkNotNull(t);
/*
* TODO(cpovirk): Consider optimizing iterator() to catch IOOBE instead of doing bounds checks.
*
* TODO(cpovirk): Consider the UnsignedBytes pattern if it performs faster and doesn't cause
* AOSP grief.
*/
return new AbstractList() {
@Override
public StackTraceElement get(int n) {
return (StackTraceElement)
invokeAccessibleNonThrowingMethod(getStackTraceElementMethod, jla, t, n);
}
@Override
public int size() {
return (Integer) invokeAccessibleNonThrowingMethod(getStackTraceDepthMethod, jla, t);
}
};
}
private static Object invokeAccessibleNonThrowingMethod(
Method method, Object receiver, Object... params) {
try {
return method.invoke(receiver, params);
} catch (IllegalAccessException e) {
throw new RuntimeException(e);
} catch (InvocationTargetException e) {
throw propagate(e.getCause());
}
}
/** JavaLangAccess class name to load using reflection */
private static final String JAVA_LANG_ACCESS_CLASSNAME = "sun.misc.JavaLangAccess";
/** SharedSecrets class name to load using reflection */
@VisibleForTesting static final String SHARED_SECRETS_CLASSNAME = "sun.misc.SharedSecrets";
/** Access to some fancy internal JVM internals. */
@Nullable private static final Object jla = getJLA();
/**
* The "getStackTraceElementMethod" method, only available on some JDKs so we use reflection to
* find it when available. When this is null, use the slow way.
*/
@Nullable
private static final Method getStackTraceElementMethod = (jla == null) ? null : getGetMethod();
/**
* The "getStackTraceDepth" method, only available on some JDKs so we use reflection to find it
* when available. When this is null, use the slow way.
*/
@Nullable
private static final Method getStackTraceDepthMethod = (jla == null) ? null : getSizeMethod();
/**
* Returns the JavaLangAccess class that is present in all Sun JDKs. It is not whitelisted for
* AppEngine, and not present in non-Sun JDKs.
*/
@Nullable
private static Object getJLA() {
try {
/*
* We load sun.misc.* classes using reflection since Android doesn't support these classes and
* would result in compilation failure if we directly refer to these classes.
*/
Class sharedSecrets = Class.forName(SHARED_SECRETS_CLASSNAME, false, null);
Method langAccess = sharedSecrets.getMethod("getJavaLangAccess");
return langAccess.invoke(null);
} catch (ThreadDeath death) {
throw death;
} catch (Throwable t) {
/*
* This is not one of AppEngine's whitelisted classes, so even in Sun JDKs, this can fail with
* a NoClassDefFoundError. Other apps might deny access to sun.misc packages.
*/
return null;
}
}
/**
* Returns the Method that can be used to resolve an individual StackTraceElement, or null if that
* method cannot be found (it is only to be found in fairly recent JDKs).
*/
@Nullable
private static Method getGetMethod() {
return getJlaMethod("getStackTraceElement", Throwable.class, int.class);
}
/**
* Returns the Method that can be used to return the size of a stack, or null if that method
* cannot be found (it is only to be found in fairly recent JDKs).
*/
@Nullable
private static Method getSizeMethod() {
return getJlaMethod("getStackTraceDepth", Throwable.class);
}
@Nullable
private static Method getJlaMethod(String name, Class... parameterTypes) throws ThreadDeath {
try {
return Class.forName(JAVA_LANG_ACCESS_CLASSNAME, false, null).getMethod(name, parameterTypes);
} catch (ThreadDeath death) {
throw death;
} catch (Throwable t) {
/*
* Either the JavaLangAccess class itself is not found, or the method is not supported on the
* JVM.
*/
return null;
}
}
}