Java的类是这样的
public class Demo {
public static void main(String[] args) {
}
private void throwE() throws ClassNotFoundException {
}
@SneakyThrows
private void t() {
throwE();
}
}
生成的class文件是这样的
public class Demo {
public Demo() {
}
public static void main(String[] args) {
}
private void throwE() throws ClassNotFoundException {
}
private void t() {
try {
this.throwE();
} catch (Throwable var2) {
throw var2;
}
}
}
Lombok 欺骗了编译器。
通过查看Lombok.sneakyThrow()的源码
/*
* Copyright (C) 2009-2017 The Project Lombok Authors.
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
package lombok;
/**
* Useful utility methods to manipulate lombok-generated code.
*/
public class Lombok {
/**
* Throws any throwable 'sneakily' - you don't need to catch it, nor declare that you throw it onwards.
* The exception is still thrown - javac will just stop whining about it.
* <p>
* Example usage:
* <pre>public void run() {
* throw sneakyThrow(new IOException("You don't need to catch me!"));
* }</pre>
* <p>
* NB: The exception is not wrapped, ignored, swallowed, or redefined. The JVM actually does not know or care
* about the concept of a 'checked exception'. All this method does is hide the act of throwing a checked exception
* from the java compiler.
* <p>
* Note that this method has a return type of {@code RuntimeException}; it is advised you always call this
* method as argument to the {@code throw} statement to avoid compiler errors regarding no return
* statement and similar problems. This method won't of course return an actual {@code RuntimeException} -
* it never returns, it always throws the provided exception.
*
* @param t The throwable to throw without requiring you to catch its type.
* @return A dummy RuntimeException; this method never returns normally, it <em>always</em> throws an exception!
*/
public static RuntimeException sneakyThrow(Throwable t) {
if (t == null) throw new NullPointerException("t");
return Lombok.<RuntimeException>sneakyThrow0(t);
}
@SuppressWarnings("unchecked")
private static <T extends Throwable> T sneakyThrow0(Throwable t) throws T {
throw (T)t;
}
/**
* Returns the parameter directly.
*
* This method can be used to prevent a static analyzer to determine the nullness of the passed parameter.
*
* @param <T> the type of the parameter.
* @param value the value to return.
* @return value (this method just returns the parameter).
*/
public static <T> T preventNullAnalysis(T value) {
return value;
}
/**
* Ensures that the {@code value} is not {@code null}.
*
* @param <T> Type of the parameter.
* @param value the value to test for null.
* @param message the message of the {@link NullPointerException}.
* @return the value if it is not null.
* @throws NullPointerException with the {@code message} if the value is null.
*/
public static <T> T checkNotNull(T value, String message) {
if (value == null) throw new NullPointerException(message);
return value;
}
}
你会发现它最终做了两件事：
空检查
重铸
两者都作为编译的一部分被删除，这就是为什么反编译代码只是重新抛出异常
这样可以用@SneakyThrows代替try{}catch{}
