配置 spring-boot 生成 jar 包
背景
从 maven 到 springboot 我们介绍了怎么从一个空的 maven 项目，一步步配置成一个 spring-boot 项目。但是还留了一个问题没有讲，那就是当我们把项目编译成 jar 包后并运行不起来。
# 编译 OK{@class=h5 text-secondary mb-4}
mvn package
[INFO] Scanning for projects...
[INFO]
[INFO] --------------------< com.sqlpy:setup-spring-boot >---------------------
[INFO] Building setup-spring-boot 1.0-SNAPSHOT
[INFO] --------------------------------[ jar ]---------------------------------
[INFO]
[INFO] --- maven-resources-plugin:3.0.1:resources (default-resources) @ setup-spring-boot ---
[INFO] Using 'UTF-8' encoding to copy filtered resources.
[INFO] skip non existing resourceDirectory /Users/jianglexing/temps/setup-spring-boot/src/main/resources
[INFO] skip non existing resourceDirectory /Users/jianglexing/temps/setup-spring-boot/src/main/resources
[INFO]
[INFO] --- maven-compiler-plugin:3.7.0:compile (default-compile) @ setup-spring-boot ---
[INFO] Changes detected - recompiling the module!
[INFO] Compiling 1 source file to /Users/jianglexing/temps/setup-spring-boot/target/classes
[INFO]
[INFO] --- maven-resources-plugin:3.0.1:testResources (default-testResources) @ setup-spring-boot ---
[INFO] Using 'UTF-8' encoding to copy filtered resources.
[INFO] skip non existing resourceDirectory /Users/jianglexing/temps/setup-spring-boot/src/test/resources
[INFO]
[INFO] --- maven-compiler-plugin:3.7.0:testCompile (default-testCompile) @ setup-spring-boot ---
[INFO] Changes detected - recompiling the module!
[INFO] Compiling 1 source file to /Users/jianglexing/temps/setup-spring-boot/target/test-classes
[INFO]
[INFO] --- maven-surefire-plugin:2.21.0:test (default-test) @ setup-spring-boot ---
[INFO]
[INFO] -------------------------------------------------------
[INFO] T E S T S
[INFO] -------------------------------------------------------
[INFO] Running com.sqlpy.AppTest
[INFO] Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.019 s - in com.sqlpy.AppTest
[INFO]
[INFO] Results:
[INFO]
[INFO] Tests run: 1, Failures: 0, Errors: 0, Skipped: 0
[INFO]
[INFO]
[INFO] --- maven-jar-plugin:3.0.2:jar (default-jar) @ setup-spring-boot ---
[INFO] Building jar: /Users/jianglexing/temps/setup-spring-boot/target/setup-spring-boot-1.0-SNAPSHOT.jar
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 2.076 s
[INFO] Finished at: 2021-09-04T13:46:18+08:00
[INFO] ------------------------------------------------------------------------
# 运行时报错{@class=h5 text-secondary mb-4}
jianglexing@NEEKYJIANG-MB2 setup-spring-boot % java -jar target/setup-spring-boot-1.0-SNAPSHOT.jar
target/setup-spring-boot-1.0-SNAPSHOT.jar中没有主清单属性
解决办法
spring 官方提供了一个编译插件，这个插件会帮我们配置 jar 的主类，所以我们只要改一下 POM 文件就行了。
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.sqlpy</groupId>
<artifactId>setup-spring-boot</artifactId>
<version>1.0-SNAPSHOT</version>
<name>setup-spring-boot</name>
<url>https://www.sqlpy.com</url>
<parent>
<artifactId>spring-boot-starter-parent</artifactId>
<groupId>org.springframework.boot</groupId>
<version>2.0.2.RELEASE</version>
</parent>
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<maven.compiler.source>1.7</maven.compiler.source>
<maven.compiler.target>1.7</maven.compiler.target>
</properties>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
<version>2.0.2.RELEASE</version>
</dependency>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.11</version>
<scope>test</scope>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
</plugin>
</plugins>
</build>
</project>
spring-boot 编译后生成的 jar 文件
jar 本质上就是一个 zip 文件，就上面的 jar 包，我们解压后可以得到如下的目录结构。
tree .
.
├── BOOT-INF
│ ├── classes
│ │ └── com
│ │ └── sqlpy
│ │ └── App.class
│ └── lib
│ ├── classmate-1.3.4.jar
│ ├── hibernate-validator-6.0.9.Final.jar
│ ├── jackson-annotations-2.9.0.jar
│ ├── jackson-core-2.9.5.jar
│ ├── jackson-databind-2.9.5.jar
│ ├── jackson-datatype-jdk8-2.9.5.jar
│ ├── jackson-datatype-jsr310-2.9.5.jar
│ ├── jackson-module-parameter-names-2.9.5.jar
│ ├── javax.annotation-api-1.3.2.jar
│ ├── jboss-logging-3.3.2.Final.jar
│ ├── jul-to-slf4j-1.7.25.jar
│ ├── log4j-api-2.10.0.jar
│ ├── log4j-to-slf4j-2.10.0.jar
│ ├── logback-classic-1.2.3.jar
│ ├── logback-core-1.2.3.jar
│ ├── slf4j-api-1.7.25.jar
│ ├── snakeyaml-1.19.jar
│ ├── spring-aop-5.0.6.RELEASE.jar
│ ├── spring-beans-5.0.6.RELEASE.jar
│ ├── spring-boot-2.0.2.RELEASE.jar
│ ├── spring-boot-autoconfigure-2.0.2.RELEASE.jar
│ ├── spring-boot-starter-2.0.2.RELEASE.jar
│ ├── spring-boot-starter-json-2.0.2.RELEASE.jar
│ ├── spring-boot-starter-logging-2.0.2.RELEASE.jar
│ ├── spring-boot-starter-tomcat-2.0.2.RELEASE.jar
│ ├── spring-boot-starter-web-2.0.2.RELEASE.jar
│ ├── spring-context-5.0.6.RELEASE.jar
│ ├── spring-core-5.0.6.RELEASE.jar
│ ├── spring-expression-5.0.6.RELEASE.jar
│ ├── spring-jcl-5.0.6.RELEASE.jar
│ ├── spring-web-5.0.6.RELEASE.jar
│ ├── spring-webmvc-5.0.6.RELEASE.jar
│ ├── tomcat-embed-core-8.5.31.jar
│ ├── tomcat-embed-el-8.5.31.jar
│ ├── tomcat-embed-websocket-8.5.31.jar
│ └── validation-api-2.0.1.Final.jar
├── META-INF
│ ├── MANIFEST.MF
│ └── maven
│ └── com.sqlpy
│ └── setup-spring-boot
│ ├── pom.properties
│ └── pom.xml
└── org
└── springframework
└── boot
└── loader
├── ExecutableArchiveLauncher.class
├── JarLauncher.class
├── LaunchedURLClassLoader$UseFastConnectionExceptionsEnumeration.class
├── LaunchedURLClassLoader.class
├── Launcher.class
├── MainMethodRunner.class
├── PropertiesLauncher$1.class
├── PropertiesLauncher$ArchiveEntryFilter.class
├── PropertiesLauncher$PrefixMatchingArchiveFilter.class
├── PropertiesLauncher.class
├── WarLauncher.class
├── archive
│ ├── Archive$Entry.class
│ ├── Archive$EntryFilter.class
│ ├── Archive.class
│ ├── ExplodedArchive$1.class
│ ├── ExplodedArchive$FileEntry.class
│ ├── ExplodedArchive$FileEntryIterator$EntryComparator.class
│ ├── ExplodedArchive$FileEntryIterator.class
│ ├── ExplodedArchive.class
│ ├── JarFileArchive$EntryIterator.class
│ ├── JarFileArchive$JarFileEntry.class
│ └── JarFileArchive.class
├── data
│ ├── RandomAccessData.class
│ ├── RandomAccessDataFile$1.class
│ ├── RandomAccessDataFile$DataInputStream.class
│ ├── RandomAccessDataFile$FileAccess.class
│ └── RandomAccessDataFile.class
├── jar
│ ├── AsciiBytes.class
│ ├── Bytes.class
│ ├── CentralDirectoryEndRecord.class
│ ├── CentralDirectoryFileHeader.class
│ ├── CentralDirectoryParser.class
│ ├── CentralDirectoryVisitor.class
│ ├── FileHeader.class
│ ├── Handler.class
│ ├── JarEntry.class
│ ├── JarEntryFilter.class
│ ├── JarFile$1.class
│ ├── JarFile$2.class
│ ├── JarFile$JarFileType.class
│ ├── JarFile.class
│ ├── JarFileEntries$1.class
│ ├── JarFileEntries$EntryIterator.class
│ ├── JarFileEntries.class
│ ├── JarURLConnection$1.class
│ ├── JarURLConnection$JarEntryName.class
│ ├── JarURLConnection.class
│ ├── StringSequence.class
│ └── ZipInflaterInputStream.class
└── util
└── SystemPropertyUtils.class
META-INF/MANIFEST.MF 配置文件的内容如下
Manifest-Version: 1.0
Implementation-Title: setup-spring-boot
Implementation-Version: 1.0-SNAPSHOT
Built-By: jianglexing
Implementation-Vendor-Id: com.sqlpy
Spring-Boot-Version: 2.0.2.RELEASE
Main-Class: org.springframework.boot.loader.JarLauncher
Start-Class: com.sqlpy.App
Spring-Boot-Classes: BOOT-INF/classes/
Spring-Boot-Lib: BOOT-INF/lib/
Created-By: Apache Maven 3.5.4
Build-Jdk: 1.8.0_282
Implementation-URL: https://www.sqlpy.com
可以看到 spring-boot 帮我们把 Main-Class 设置成了它内部的一个包 org.springframework.boot.loader.JarLauncher 。
在我们不添加编译插件的情况下 MANIFEST.MF 的内容是这样的。
Manifest-Version: 1.0
Implementation-Title: setup-spring-boot
Implementation-Version: 1.0-SNAPSHOT
Built-By: jianglexing
Implementation-Vendor-Id: com.sqlpyl
Created-By: Apache Maven 3.5.4
Build-Jdk: 1.8.0_282
Implementation-URL: https://www.sqlpy.com