在之前spring boot3文章中我们介绍了，spring boot3的一个重要特性就是支持把spring boot3的应用编译成为GraalVM的Native Image。
今天我们用具体的例子来给大家演示一下如何正确的将spring boot3的应用编译成为native image。
安装GraalVM
如果要把spring boot3的app编译成为native应用，需要GraalVM的支持。
什么是GraalVM呢？
从名字就可以看出来GraalVM是一个虚拟机，它的主要目标就是提升java应用程序的性能，并且消耗更少的资源。
它在java HotSpot JVM的基础上添加了JIT编译器和AOT来实现将应用编译成为本地可执行文件。除了java之外，GraalVM还支持JavaScript、Ruby、Python等多种编程语言。
所以，为什么要用GraalVM呢？一个字：快。
安装GraalVM也比较简单，我们进入它的官方下载页面下载对应的版本即可：https://www.oracle.com/downloads/graalvm-downloads.html。
GraalVM跟JDK一样也有两个版本，社区版和企业版本，大家可以根据需要自行选择。
要注意的是spring boot3需要GraalVM 22.3以上的版本支持，大家可不要下载错了。
下载完成之后，我们可以像正常安装JDK一样来安装GraalVM,这里以mac为例，假如我们安装的目录是/Library/Java/JavaVirtualMachines/graalvm-ee-java17-22.3.0，那么我们需要配置对应的JAVA_HOME和PATH环境变量如下：
export PATH=/Library/Java/JavaVirtualMachines/graalvm-ee-java17-22.3.0/Contents/Home/bin:$PATH
export JAVA_HOME=/Library/Java/JavaVirtualMachines/graalvm-ee-java17-22.3.0/Contents/Home
PATH中有一个非常重要的命令叫做gu，如果不添加PATH，那么在使用中就可能遇到下面的异常：
'gu' tool wasn't found. This probably means that JDK at isn't a GraalVM distribution.
安装完毕之后可以通过下面的命令来进行验证：
java -version
java version "17.0.5" 2022-10-18 LTS
Java(TM) SE Runtime Environment GraalVM EE 22.3.0 (build 17.0.5+9-LTS-jvmci-22.3-b07)
Java HotSpot(TM) 64-Bit Server VM GraalVM EE 22.3.0 (build 17.0.5+9-LTS-jvmci-22.3-b07, mixed mode, sharing)
如果是在mac环境下，还需要执行下面的命令来解除对graalvm的隔离限制：
sudo xattr -r -d com.apple.quarantine /path/to/graalvm
否则在使用中就会遇到下面的问题：
添加Native Image支持
我们安装GraalVM的目的就是使用它的native Image特性。native image是一个单独的jar包，我们可以执行下面的命令来进行安装：
gu install native-image
其中gu就是/Library/Java/JavaVirtualMachines/graalvm-ee-java17-22.3.0/Contents/Home/bin中的命令。
下载的过程中还需要输入一个有效的邮件，并进行邮箱校验。然后一路ENTER就可以了。
当然，你还可以把Oracle GraalVM Enterprise Edition Native Image下载到本地，然后使用gu install -L来进行本地安装。
好了，到目前为止，一切准备妥当，我们接下来看看如何把spring boot3的应用打包成为native image吧。
构建spring boot3应用
这里我们使用的是maven，所以需要添加下面的spring boot3的依赖：
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>3.0.1</version>
<relativePath/>
</parent>
因为要构建native image，所以我们还需要用到下面的一个native-maven-plugin插件：
<plugin>
<groupId>org.graalvm.buildtools</groupId>
<artifactId>native-maven-plugin</artifactId>
</plugin>
这里我们只创建了一个非常简单的main方法：
@SpringBootApplication
public class NativeImageApplication {
public static void main(String[] args) {
SpringApplication.run(NativeImageApplication.class, args);
}
}
然后，我们尝试运行 mvn native:build来构建spring boot3应用程序。
记得在build之前一定先要编译好项目。
很可惜，你会发现下面的异常：
[INFO] --- native-maven-plugin:0.9.19:build (default-cli) @ native-image ---
[WARNING] 'native:build' goal is deprecated. Use 'native:compile-no-fork' instead.
[INFO] Found GraalVM installation from JAVA_HOME variable.
...
Error: Please specify class (or <module>/<mainclass>) containing the main entry point method. (see --help)
从上面的异常我们发现了两个问题，第一个问题是一个警告，它推荐我们使用native:compile-no-fork。
第二个问题是说找不到mainclass,根据异常信息，我们在pom的plugin中添加下面的配置信息，如下所示：
<plugin>
<groupId>org.graalvm.buildtools</groupId>
<artifactId>native-maven-plugin</artifactId>
<configuration>
<!-- imageName用于设置生成的二进制文件名称 -->
<imageName>${project.artifactId}</imageName>
<!-- mainClass用于指定main方法类路径 -->
<mainClass>com.flydean.nativeimage.NativeImageApplication</mainClass>
<buildArgs>
--no-fallback
</buildArgs>
</configuration>
<executions>
<execution>
<id>build-native</id>
<goals>
<goal>compile-no-fork</goal>
</goals>
<phase>package</phase>
</execution>
</executions>
</plugin>
然后重新运行mvn native:compile-no-fork：
GraalVM Native Image: Generating 'native-image' (executable)...
========================================================================================================================
[1/7] Initializing... (4.3s @ 0.25GB)
Version info: 'GraalVM 22.3.0 Java 17 EE'
Java version info: '17.0.5+9-LTS-jvmci-22.3-b07'
C compiler: cc (apple, arm64, 14.0.0)
Garbage collector: Serial GC
1 user-specific feature(s)
- org.springframework.aot.nativex.feature.PreComputeFieldFeature
Field org.apache.commons.logging.LogAdapter#log4jSpiPresent set to true at build time
Field org.apache.commons.logging.LogAdapter#log4jSlf4jProviderPresent set to true at build time
Field org.apache.commons.logging.LogAdapter#slf4jSpiPresent set to true at build time
Field org.apache.commons.logging.LogAdapter#slf4jApiPresent set to true at build time
Field org.springframework.core.NativeDetector#imageCode set to true at build time
Field org.springframework.core.KotlinDetector#kotlinPresent set to false at build time
Field org.springframework.core.KotlinDetector#kotlinReflectPresent set to false at build time
Field org.springframework.format.support.DefaultFormattingConversionService#jsr354Present set to false at build time
Field org.springframework.cglib.core.AbstractClassGenerator#imageCode set to true at build time
[2/7] Performing analysis... [**********] (24.8s @ 4.57GB)
10,266 (89.50%) of 11,470 classes reachable
16,675 (63.53%) of 26,248 fields reachable
53,776 (60.71%) of 88,575 methods reachable
469 classes, 140 fields, and 2,281 methods registered for reflection
63 classes, 69 fields, and 55 methods registered for JNI access
5 native libraries: -framework CoreServices, -framework Foundation, dl, pthread, z
[3/7] Building universe... (5.0s @ 2.72GB)
[4/7] Parsing methods... [**] (4.4s @ 2.42GB)
[5/7] Inlining methods... [***] (1.3s @ 3.87GB)
[6/7] Compiling methods... [********] (70.0s @ 1.04GB)
[7/7] Creating image... (4.7s @ 3.35GB)
30.27MB (58.75%) for code area: 30,771 compilation units
20.50MB (39.79%) for image heap: 305,579 objects and 93 resources
769.52KB ( 1.46%) for other data
51.52MB in total
------------------------------------------------------------------------------------------------------------------------
Top 10 packages in code area: Top 10 object types in image heap:
2.02MB com.oracle.svm.core.code 5.79MB byte[] for code metadata
1.77MB sun.security.ssl 2.31MB byte[] for java.lang.String
1.29MB java.util 2.09MB byte[] for general heap data
929.52KB java.lang.invoke 2.07MB java.lang.String
925.96KB com.sun.crypto.provider 1.76MB java.lang.Class
802.99KB java.lang 671.09KB byte[] for embedded resources
633.35KB sun.nio.ch 567.26KB byte[] for reflection metadata
625.89KB java.util.concurrent 481.22KB com.oracle.svm.core.hub.DynamicHubCompanion
601.86KB org.apache.tomcat.util.net 450.06KB java.util.HashMap$Node
594.48KB sun.security.x509 401.78KB java.util.concurrent.ConcurrentHashMap$Node
20.02MB for 397 more packages 3.40MB for 2297 more object types
------------------------------------------------------------------------------------------------------------------------
9.5s (7.9% of total time) in 50 GCs | Peak RSS: 3.75GB | CPU load: 4.39
------------------------------------------------------------------------------------------------------------------------
Produced artifacts:
/Users/learn-springboot3/learn-springboot3/native-image/target/native-image (executable)
/Users/learn-springboot3/learn-springboot3/native-image/target/native-image.build_artifacts.txt (txt)
========================================================================================================================
Finished generating 'native-image' in 2m 0s.
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 02:01 min
[INFO] Finished at: 2023-01-05T20:43:39+08:00
[INFO] ------------------------------------------------------------------------
经过漫长的等待，我们终于build完成了。
因为我们的artifactId叫做native-image,所以最终在target目录下面生成了一个叫做native-image的可执行文件：
.
├── classes
│ ├── application.properties
│ └── com
│ └── flydean
│ └── nativeimage
│ └── NativeImageApplication.class
├── generated-sources
│ └── annotations
├── generated-test-sources
│ └── test-annotations
├── maven-archiver
│ └── pom.properties
├── maven-status
│ └── maven-compiler-plugin
│ ├── compile
│ │ └── default-compile
│ │ ├── createdFiles.lst
│ │ └── inputFiles.lst
│ └── testCompile
│ └── default-testCompile
│ ├── createdFiles.lst
│ └── inputFiles.lst
├── native-image
├── native-image-0.0.1-SNAPSHOT.jar
├── native-image-0.0.1-SNAPSHOT.jar.original
├── native-image.build_artifacts.txt
├── surefire-reports
│ ├── TEST-com.flydean.nativeimage.NativeImageApplicationTests.xml
│ └── com.flydean.nativeimage.NativeImageApplicationTests.txt
└── test-classes
└── com
└── flydean
└── nativeimage
└── NativeImageApplicationTests.class
20 directories, 14 files
如果你这时候运行target/native-image,那么很可能得到下面的异常：
[main] DEBUG org.springframework.context.aot.AotApplicationContextInitializer - Initializing ApplicationContext with AOT
[main] ERROR org.springframework.boot.SpringApplication - Application run failed
java.lang.IllegalArgumentException: Could not find class [com.flydean.nativeimage.NativeImageApplication__ApplicationContextInitializer]
at org.springframework.util.ClassUtils.resolveClassName(ClassUtils.java:333)
这是因为我们缺少一些spring boot的AOT元文件信息，正确的做法是使用下面的命令：
mvn clean package -Pnative
它实际上执行的是下面的几个命令：
mvn spring-boot:process-aot
mvn spring-boot:process-test-aot
mvn spring-boot:build-image
最终我们得到编译好的native-image信息，运行得到下面的结果：
2023-01-05T17:07:11.692+08:00 INFO 69299 --- [ main] c.f.nativeimage.NativeImageApplication : Starting AOT-processed NativeImageApplication using Java 17.0.5 with PID 69299 (/Users/wayne/data/git/ddean2009/learn-springboot3/learn-springboot3/native-image/target/native-image started by wayne in /Users/wayne/data/git/ddean2009/learn-springboot3/learn-springboot3/native-image)
2023-01-05T17:07:11.693+08:00 INFO 69299 --- [ main] c.f.nativeimage.NativeImageApplication : No active profile set, falling back to 1 default profile: "default"
2023-01-05T17:07:11.709+08:00 INFO 69299 --- [ main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat initialized with port(s): 8080 (http)
2023-01-05T17:07:11.710+08:00 INFO 69299 --- [ main] o.apache.catalina.core.StandardService : Starting service [Tomcat]
2023-01-05T17:07:11.710+08:00 INFO 69299 --- [ main] o.apache.catalina.core.StandardEngine : Starting Servlet engine: [Apache Tomcat/10.1.4]
2023-01-05T17:07:11.717+08:00 INFO 69299 --- [ main] o.a.c.c.C.[Tomcat].[localhost].[/] : Initializing Spring embedded WebApplicationContext
2023-01-05T17:07:11.717+08:00 INFO 69299 --- [ main] w.s.c.ServletWebServerApplicationContext : Root WebApplicationContext: initialization completed in 24 ms
2023-01-05T17:07:11.729+08:00 INFO 69299 --- [ main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat started on port(s): 8080 (http) with context path ''
2023-01-05T17:07:11.729+08:00 INFO 69299 --- [ main] c.f.nativeimage.NativeImageApplication : Started NativeImageApplication in 0.053 seconds (process running for 0.072)
总结
从运行情况来看，native-image的启动速度非常快，应该可以提升不少的性能。
感兴趣的小伙伴赶紧用起来吧。