Lombok 的@SneakyThrows的作用

ゝ一纸荒年。 2023-09-29 12:24 20阅读 0赞

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.
 	 * 
 	 * Example usage:
 	 * <pre>public void run() {
 	 * throw sneakyThrow(new IOException("You don't need to catch me!"));
 	 * }</pre>
 	 * 
 	 * 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.
 	 * 
 	 * 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 always 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\{\}