The input is empty. You have to specify one or more '-injars' options

[takeAction]

spring boot 2.x, jdk 1.8, maven 3.5, proguard 7.2.2 and proguard-maven-plugin 2.6.0.
my configuration as follows:

<properties>

		<war.output.dictionary>wars/</war.output.dictionary>

</properties>
....
<build>
		...
		<plugins>
						
			<plugin>
				<groupId>org.apache.maven.plugins</groupId>
				<artifactId>maven-war-plugin</artifactId>				
				<configuration>
					<outputDirectory>${war.output.dictionary}</outputDirectory>
				</configuration>
			</plugin>
			<plugin>
				<groupId>com.github.wvengen</groupId>
				<artifactId>proguard-maven-plugin</artifactId>
				<version>2.6.0</version>
				<executions>
					<execution>
						<phase>compile</phase>
						<goals>
							<goal>proguard</goal>
						</goals>
					</execution>
				</executions>
				<configuration>
					<proguardVersion>7.2.2</proguardVersion>
					<obfuscate>true</obfuscate>
					<proguardInclude>E:/proguard.cfg</proguardInclude>
					<libs>
						<lib>${java.home}/lib/rt.jar</lib>
					</libs>
					<injar>classes</injar>
					<outputDirectory>proguard</outputDirectory>
				</configuration>
				<dependencies>
					<dependency>
						<groupId>com.guardsquare</groupId>
						<artifactId>proguard-base</artifactId>
						<version>7.2.2</version>
						<scope>runtime</scope>
					</dependency>
				</dependencies>
			</plugin>
		</plugins>
		
		<resources>
			<resource>
				<directory>src/main/resources</directory>  
                <filtering>true</filtering>
                <includes>
                	<include>**/*.properties</include>
                	<include>**/*.yml</include><!-- 也可以指定具体的文件 application-${env}.yml -->
                </includes>                
			</resource>
			<resource>
				<directory>src/main/resources</directory>
				<filtering>false</filtering>
				<excludes>
					<exclude>**/*.properties</exclude>
					<exclude>**/*.yml</exclude>
				</excludes>
			</resource>
		</resources>
		
	</build>

my project is packaged as war.
I want to obfuscate the war or its classes, when I execute mvn clean package in idea, the error thrown:

[proguard] ProGuard, version 7.2.2
 [proguard] Unexpected error
 [proguard] java.io.IOException: The input is empty. You have to specify one or more '-injars' options.
 [proguard] 	at proguard.ConfigurationChecker.check(ConfigurationChecker.java:62) ~[proguard-base-7.2.2.jar:7.2.2]
 [proguard] 	at proguard.ProGuard.checkConfiguration(ProGuard.java:290) ~[proguard-base-7.2.2.jar:7.2.2]
 [proguard] 	at proguard.ProGuard.execute(ProGuard.java:99) ~[proguard-base-7.2.2.jar:7.2.2]
 [proguard] 	at proguard.ProGuard.main(ProGuard.java:623) [proguard-base-7.2.2.jar:7.2.2]

what's the problem? I have set injar as classes and phase of execution as compile.

[lasselindqvist]

Based on your code, your injar parameter points to a directory of class files, not a JAR file. Try changing that.

[takeAction]

@lasselindqvist but from plugin.xml of proguard-maven-plugin, it says the injar is about

Specifies the input jar name (or wars, ears, zips) of the application to be processed. You may specify a classes directory e. g. 'classes'. This way plugin will processed the classes instead of jar. You would need to bind the execution to phase 'compile' or 'process-classes' in this case.

does I misunderstand it?

[lasselindqvist]

You can see the parameter here: https://github.com/wvengen/proguard-maven-plugin/blob/master/src/main/java/com/github/wvengen/maven/proguard/ProGuardMojo.java#L192

See https://github.com/wvengen/proguard-maven-plugin/blob/master/src/main/java/com/github/wvengen/maven/proguard/ProGuardMojo.java#L434 about what happens if that directory does not exist. You have given outputDirectory parameter and maybe that is what breaks you usage of it.

Why is outputDirectory also used as input directory? I have no idea and it preceeds my time. Maybe there could be a separate inputDirectory which could default to outputDirectory if none specified (for compatibility reasons), but there is none. If you need such a solution, I could merge and release such a change.

[takeAction]

I added outputDirectory of proguard-maven-plugin in my case because I want to generate the obfuscated classes in the specified folder under target directory.

After I remove this parameter, this error gone, the obfuscated classes are in classes folder and the un-obfuscated classes are in classes_proguard_base folder.
Thanks @lasselindqvist !