最近在MINGW64控制台中使用 maven 命令打包时出现如下错误。通常在 eclipse 或 IDEA这样的集成开发工具中，只要将工程的JDK环境变量重新设置一下，重新执行一下maven 打包命令即可。
1 [INFO] ------------------------------------------------------------------------ 2 [INFO] BUILD FAILURE 3 [INFO] ------------------------------------------------------------------------ 4 [INFO] Total time: 1.628 s 5 [INFO] Finished at: 2018-08-21T12:05:46+08:00 6 [INFO] ------------------------------------------------------------------------ 7 [ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.7.0:compile (default-compile) on project xxx-framework: Compilation failure 8 [ERROR] No compiler is provided in this environment. Perhaps you are running on a JRE rather than a JDK? 9 [ERROR] 10 [ERROR] -> [Help 1] 11 org.apache.maven.lifecycle.LifecycleExecutionException: Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.7.0:compile (default-compile) on project xxx-framework: Compilation failure 12 No compiler is provided in this environment. Perhaps you are running on a JRE rather than a JDK? 13 14 at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:213) 15 at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:154) 16 at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:146) 17 at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject (LifecycleModuleBuilder.java:117) 18 at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject (LifecycleModuleBuilder.java:81) 19 at org.apache.maven.lifecycle.internal.builder.singlethreaded.SingleThreadedBuilder.build (SingleThreadedBuilder.java:56) 20 at org.apache.maven.lifecycle.internal.LifecycleStarter.execute (LifecycleStarter.java:128) 21 at org.apache.maven.DefaultMaven.doExecute (DefaultMaven.java:305) 22 at org.apache.maven.DefaultMaven.doExecute (DefaultMaven.java:192) 23 at org.apache.maven.DefaultMaven.execute (DefaultMaven.java:105) 24 at org.apache.maven.cli.MavenCli.execute (MavenCli.java:956) 25 at org.apache.maven.cli.MavenCli.doMain (MavenCli.java:290) 26 at org.apache.maven.cli.MavenCli.main (MavenCli.java:194) 27 at sun.reflect.NativeMethodAccessorImpl.invoke0 (Native Method) 28 at sun.reflect.NativeMethodAccessorImpl.invoke (Unknown Source) 29 at sun.reflect.DelegatingMethodAccessorImpl.invoke (Unknown Source) 30 at java.lang.reflect.Method.invoke (Unknown Source) 31 at org.codehaus.plexus.classworlds.launcher.Launcher.launchEnhanced (Launcher.java:289) 32 at org.codehaus.plexus.classworlds.launcher.Launcher.launch (Launcher.java:229) 33 at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode (Launcher.java:415) 34 at org.codehaus.plexus.classworlds.launcher.Launcher.main (Launcher.java:356) 35 Caused by: org.apache.maven.plugin.compiler.CompilationFailureException: Compilation failure 36 No compiler is provided in this environment. Perhaps you are running on a JRE rather than a JDK? 37 38 at org.apache.maven.plugin.compiler.AbstractCompilerMojo.execute (AbstractCompilerMojo.java:1161) 39 at org.apache.maven.plugin.compiler.CompilerMojo.execute (CompilerMojo.java:168) 40 at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo (DefaultBuildPluginManager.java:137) 41 at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:208) 42 at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:154) 43 at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:146) 44 at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject (LifecycleModuleBuilder.java:117) 45 at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject (LifecycleModuleBuilder.java:81) 46 at org.apache.maven.lifecycle.internal.builder.singlethreaded.SingleThreadedBuilder.build (SingleThreadedBuilder.java:56) 47 at org.apache.maven.lifecycle.internal.LifecycleStarter.execute (LifecycleStarter.java:128) 48 at org.apache.maven.DefaultMaven.doExecute (DefaultMaven.java:305) 49 at org.apache.maven.DefaultMaven.doExecute (DefaultMaven.java:192) 50 at org.apache.maven.DefaultMaven.execute (DefaultMaven.java:105) 51 at org.apache.maven.cli.MavenCli.execute (MavenCli.java:956) 52 at org.apache.maven.cli.MavenCli.doMain (MavenCli.java:290) 53 at org.apache.maven.cli.MavenCli.main (MavenCli.java:194) 54 at sun.reflect.NativeMethodAccessorImpl.invoke0 (Native Method) 55 at sun.reflect.NativeMethodAccessorImpl.invoke (Unknown Source) 56 at sun.reflect.DelegatingMethodAccessorImpl.invoke (Unknown Source) 57 at java.lang.reflect.Method.invoke (Unknown Source) 58 at org.codehaus.plexus.classworlds.launcher.Launcher.launchEnhanced (Launcher.java:289) 59 at org.codehaus.plexus.classworlds.launcher.Launcher.launch (Launcher.java:229) 60 at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode (Launcher.java:415) 61 at org.codehaus.plexus.classworlds.launcher.Launcher.main (Launcher.java:356) 62 [ERROR] 63 [ERROR] 64 [ERROR] For more information about the errors and possible solutions, please read the following articles: 65 [ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/MojoFailureException 66 [ERROR] 67 [ERROR] After correcting the problems, you can resume the build with the command
[ERROR] mvn <goals> -rf :xxx-framework
错误源头分析：
我试了一下，在IDEA中是可以正常执行maven打包命令。由于这种错误出现过很多次，但是却不知道其背后的原因，这次又碰到了，于是决定从源头上看看究竟是什么原因导致的。根据上面的异常提示信息，一路追踪下来，发现异常是从这个类（如下所示，该类位于plexus-compiler-javac-2.8.2.jar 之中）的方法抛出来的。
org.codehaus.plexus.compiler.javac.JavaxToolsCompiler.compileInProcess(String[], CompilerConfiguration, String[])
很容易看出来是compiler等于null，导致出错。而compiler变量是由执行 getJavaCompiler 方法后赋值的。进入到这个方法（如下所示，该方法位于plexus-compiler-javac-2.8.2.jar 之中）里面去看看。
org.codehaus.plexus.compiler.javac.JavaxToolsCompiler.getJavaCompiler(CompilerConfiguration)
1 protected static JavaCompiler getJavaCompiler( CompilerConfiguration compilerConfiguration ) 2 { 3 switch ( compilerConfiguration.getCompilerReuseStrategy() ) 4 { 5 case AlwaysNew: 6 return ToolProvider.getSystemJavaCompiler(); 7 case ReuseCreated: //打断点跟踪会执行此处 8 JavaCompiler javaCompiler; 9 synchronized ( JAVA_COMPILERS ) 10 { 11 if ( JAVA_COMPILERS.size() > 0 ) 12 { 13 javaCompiler = JAVA_COMPILERS.get( 0 ); 14 JAVA_COMPILERS.remove( javaCompiler ); 15 return javaCompiler; 16 } 17 } 18 javaCompiler = ToolProvider.getSystemJavaCompiler(); 19 return javaCompiler; 20 case ReuseSame: 21 default: 22 return COMPILER; 23 } 24 25 }
打断点跟踪了一下，会执行 ReuseCreated 分支。JAVA_COMPILERS 列表大小为空，执行 ToolProvider.getSystemJavaCompiler()，进入到这个方法中，发现这个方法查找某接口的实现类（如下所示），然后加载该实现类并实例化。
javax.tools.ToolProvider.getSystemJavaCompiler()
private static final String defaultJavaCompilerName= "com.sun.tools.javac.api.JavacTool";
跟踪到这儿，看到com.sun这个包我一时半会儿还没有反应过来，这个是JDK私有的包。既然了找不到实现类，那我就创建一个实现该接口的类，这样的话就不会报错了，然而当我把眼光停留到控制台那行红色错误提示信息上面，心想是不是应该使用 mvn -v 命令看一下，是不是加载的JDK路径不对导致的？ 在 MINGW64 中执行 mvn -v 命令，控制台打印出来的信息如下所示：
1 $ mvn -v 2 Apache Maven 3.5.3 (3383c37e1f9e9b3bc3df5050c29c8aff9f295297; 2018-02-25T03:49:05+08:00) 3 Maven home: D:progapache-maven-3.5.3 4 Java version: 1.8.0_161, vendor: Oracle Corporation 5 Java home: C:Program FilesJavajre 6 Default locale: zh_CN, platform encoding: GBK 7 OS name: "windows 7", version: "6.1", arch: "amd64", family: "windows"
看到控制台输出的Java home路径，跟我在环境中配置的JAVA_HOME路径不一样，奇怪了？ 打开cmd， 在cmd命令行中执行 mvn -v 命令，控制台打印出来的信息如下所示：
1 C:Usershyt>mvn -v 2 Apache Maven 3.5.3 (3383c37e1f9e9b3bc3df5050c29c8aff9f295297; 2018-02-25T03:49:05+08:00) 3 Maven home: D:progapache-maven-3.5.3in.. 4 Java version: 1.8.0_161, vendor: Oracle Corporation 5 Java home: C:Program FilesJavajdk1.8.0_161jre 6 Default locale: zh_CN, platform encoding: GBK 7 OS name: "windows 7", version: "6.1", arch: "amd64", family: "windows"
对比之后，发现两者不一样，打开maven源码工程，看一下执行 mvn -v 命令的输出版本信息的方法，看一下究竟是从什么地方读取JDK的路径信息的。
org.apache.maven.cli.MavenCli#version private void version( CliRequest cliRequest ) { if ( cliRequest.debug || cliRequest.commandLine.hasOption( CLIManager.SHOW_VERSION ) ) { System.out.println( CLIReportingUtils.showVersion() ); } }
org.apache.maven.cli.CLIReportingUtils#showVersion public static String showVersion() { final String ls = System.getProperty( "line.separator" ); Properties properties = getBuildProperties(); StringBuilder version = new StringBuilder( 256 ); version.append( buffer().strong( createMavenVersionString( properties ) ) ).append( ls ); version.append( reduce( properties.getProperty( "distributionShortName" ) + " home: " + System.getProperty( "maven.home", "<unknown Maven " + "home>" ) ) ) .append( ls ); version.append( "Java version: " ).append( System.getProperty( "java.version", "<unknown Java version>" ) ).append( ", vendor: " ).append( System.getProperty( "java.vendor", "<unknown vendor>" ) ).append( ", runtime: " ).append( System.getProperty( "java.home", "<unknown runtime>" ) ).append( ls ); version.append( "Default locale: " ).append( Locale.getDefault() ).append( ", platform encoding: " ).append( System.getProperty( "file.encoding", "<unknown encoding>" ) ).append( ls ); version.append( "OS name: "" ).append( Os.OS_NAME ).append( "", version: "" ).append( Os.OS_VERSION ).append( "", arch: "" ).append( Os.OS_ARCH ).append( "", family: "" ).append( Os.OS_FAMILY ).append( '"' ); return version.toString(); }
看到这儿我明白了，是在执行mvn命令的时候传入JDK路径不正确，我手动传入JDK路径来试试看能不能解决这个问题。我找到mvn.cmd文件，在该文件中（如下所示位置，使用notepad++编辑打开）设置JAVA_HOME路径，在 MINGW64 中执行 mvn install 依然提示错误信息，mvn -v 打印出的信息中 java home 路径依然是错误的。mvn -DJAVA_HOME=C:/Program Files/Java/jdk1.8.0_161/ install 采用这样的方式强制传入JAVA_HOME参数，导致maven根本无法识别 install 命令。
看来得研究一下 MINGW64 和 cmd 这两者为什么打印出来的JDK路径不一样，难不成 MINGW64 没有读取系统环境变量。 不过在此之前我要先尝试一下在 maven-compile-plugin 插件中增加<forceJavacCompilerUse>true</forceJavacCompilerUse> 配置项。因为前面代码提示 compiler 为空，是因为使用了JavaxToolsCompiler来编译源代码，我让maven直接使用javac命令来编译源代码，这样就不会提示找不到complier,从而compiler为null，这样做因该不会出错。
org.codehaus.plexus.compiler.javac.JavacCompiler.performCompile(CompilerConfiguration)
//省略方法 if ( isJava16() && !config.isForceJavacCompilerUse() ) { // use fqcn to prevent loading of the class on 1.5 environment ! result =org.codehaus.plexus.compiler.javac.JavaxToolsCompiler.compileInProcess( args, config, sourceFiles ); } else { result = compileInProcess( args, config ); }
在工程的 pom.xml 文件中为 maven-compile-plugin 插件中增加 <forceJavacCompilerUse>true</forceJavacCompilerUse> 配置项。
1 <plugin> 2 <groupId>org.apache.maven.plugins</groupId> 3 <artifactId>maven-compiler-plugin</artifactId> 4 <!-- since 2.0 --> 5 <version>3.7.0</version> 6 <configuration> 7 <!-- use the Java 8 language features --> 8 <source>1.8</source> 9 <!-- want the compiled classes to be compatible with JVM 1.8 --> 10 <target>1.8</target> 11 <!-- The -encoding argument for the Java compiler. --> 12 <encoding>UTF8</encoding> 13 <forceJavacCompilerUse>true</forceJavacCompilerUse> 14 </configuration> 15 </plugin>
在 MINGW64 中执行 mvn install 命令，错误依旧
[ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.7.0:compile (default-compile) on project xxx-framework: Fatal error compiling: tools.jar not found: C:Program FilesJavajre..lib ools.jar -> [Help 1] [ERROR] [ERROR] To see the full stack trace of the errors, re-run Maven with the -e switch. [ERROR] Re-run Maven using the -X switch to enable full debug logging. [ERROR] [ERROR] For more information about the errors and possible solutions, please read the following articles: [ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/MojoExecutionException
没办法，回到设置 MINGW64 读取windows环境变量的路子上来，只有这样才能读取正确的JDK路径。可是在网上找了好长时间，都是说如何设置 MINGW64 的C++ gcc环境变量之类，不是自己想要。猛然脑海中想到3个字“注册表”。果然在“注册表”中找到与JDK相关的配置项。
HKEY_LOCAL_MACHINESOFTWAREJavaSoftJava Runtime Environment
问题的解决办法：
编辑注册表中相关的配置项，来解决这个问题。配置如下所示：
使用上面的配置之后，在 MINGW64 中执行 mvn install 命令之后，控制台提示报错。
$ mvn install
Error: could not open `C:Program FilesJavajdk1.8.0_161libamd64jvm.cfg'
我在这个目录下面去看了一下，果然没有这个文件。在这个路径 C:Program FilesJavajdk1.8.0_161jrelibamd64 才有相关的配置，修改一下配置，如下所示：
在 MINGW64 中执行mvn install命令，控制台提示打包成功，mvn -v 输出的信息显示jdk路径也配置正确。
原因分析：
对 C:Program FilesJavajre 和 C:Program FilesJavajdk1.8.0_161jre 这二者之间的区别没有弄清楚。开发的时候要指向JDK中的jre，因为要根据该jre的位置来做定位，加载JDK中的相关资源。比如上面maven要加载JDK中的com.sun私有包。关于这二者的区别可以在网上搜索，有关这方面的文章挺多的。
附CSDN上的某篇文章： java中的两个jre区别 https://blog.csdn.net/sanjiaozhen/article/details/45157565