Spring Boot的Maven插件（Spring Boot Maven plugin）能够以Maven的方式为应用提供Spring Boot的支持，即为Spring Boot应用提供了执行Maven操作的可能。
Spring Boot Maven plugin能够将Spring Boot应用打包为可执行的jar或war文件，然后以通常的方式运行Spring Boot应用。
Spring Boot Maven plugin的最新版本为2017.6.8发布的1.5.4.RELEASE，要求Java 8, Maven 3.2及以后。
Spring Boot Maven plugin的5个Goals
- spring-boot:repackage，默认goal。在mvn package之后，再次打包可执行的jar/war，同时保留mvn package生成的jar/war为.origin
- spring-boot:run，运行Spring Boot应用
- spring-boot:start，在mvn integration-test阶段，进行Spring Boot应用生命周期的管理
- spring-boot:stop，在mvn integration-test阶段，进行Spring Boot应用生命周期的管理
- spring-boot:build-info，生成Actuator使用的构建信息文件build-info.properties
配置pom.xml文件
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
<version>2.0.1.RELEASE</version>
<executions>
<execution>
<goals>
<goal>repackage</goal>
</goals>
</execution>
</executions>
</plugin>
</plugins>
</build>
mvn package spring-boot:repackage说明
Spring Boot Maven plugin的最主要goal就是repackage，其在Maven的package生命周期阶段，能够将mvn package生成的软件包，再次打包为可执行的软件包，并将mvn package生成的软件包重命名为*.original。
基于上述配置，对一个生成Jar软件包的项目执行如下命令
可以看到生成的两个jar文件，一个是*.jar，另一个是*.jar.original。在执行上述命令的过程中，Maven首先在package阶段打包生成*.jar文件；然后执行spring-boot:repackage重新打包，查找Manifest文件中配置的Main-Class属性，如下所示：
Manifest-Version: 1.0
Implementation-Title: gs-consuming-rest
Implementation-Version: 0.1.0
Archiver-Version: Plexus Archiver
Built-By: exihaxi
Implementation-Vendor-Id: org.springframework
Spring-Boot-Version: 1.5.3.RELEASE
Implementation-Vendor: Pivotal Software, Inc.
Main-Class: org.springframework.boot.loader.JarLauncher
Start-Class: com.ericsson.ramltest.MyApplication
Spring-Boot-Classes: BOOT-INF/classes/
Spring-Boot-Lib: BOOT-INF/lib/
Created-By: Apache Maven 3.5.0
Build-Jdk: 1.8.0_131
注意，其中的Main-Class属性值为org.springframework.boot.loader.JarLauncher；
Start-Class属性值为com.ericsson.ramltest.MyApplication。
其中com.ericsson.ramltest.MyApplication类中定义了main()方法，是程序的入口。
通常，Spring Boot Maven plugin会在打包过程中自动为Manifest文件设置Main-Class属性，事实上该属性究竟作用几何，还可以受Spring Boot Maven plugin的配置属性layout控制的，示例如下
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
<version>1.5.4.RELEASE</version>
<configuration>
<mainClass>${start-class}</mainClass>
<layout>ZIP</layout>
</configuration>
<executions>
<execution>
<goals>
<goal>repackage</goal>
</goals>
</execution>
</executions>
</plugin>
layout属性的值可以如下：
Main-Class: org.springframework.boot.loader.JarLauncher
- WAR，即通常的可执行war，需要的servlet容器依赖位于WEB-INF/lib-provided
Main-Class: org.springframework.boot.loader.warLauncher
Main-Class: org.springframework.boot.loader.PropertiesLauncher
- MODULE，将所有的依赖库打包（scope为provided的除外），但是不打包Spring Boot的任何Launcher
- NONE，将所有的依赖库打包，但是不打包Spring Boot的任何Launcher
RepackageMojo的关键方法execute：
@Override
public void execute() throws MojoExecutionException, MojoFailureException {
if (this.project.getPackaging().equals("pom")) {
getLog().debug("repackage goal could not be applied to pom project.");
return;
}
if (this.skip) {
getLog().debug("skipping repackaging as per configuration.");
return;
}
//得到项目中的原始的jar，就是使用maven-jar-plugin生成的jar
File source = this.project.getArtifact().getFile();
//要写入的目标文件，就是fat jar
File target = getTargetFile();
Repackager repackager = new Repackager(source) {
//从source中寻找spring boot 应用程序入口的main方法。
@Override
protected String findMainMethod(JarFile source) throws IOException {
long startTime = System.currentTimeMillis();
try {
return super.findMainMethod(source);
}
finally {
long duration = System.currentTimeMillis() - startTime;
if (duration > FIND_WARNING_TIMEOUT) {
getLog().warn("Searching for the main-class is taking some time, "
+ "consider using the mainClass configuration "
+ "parameter");
}
}
}
};
//如果插件中指定了mainClass就直接使用
repackager.setMainClass(this.mainClass);
if (this.layout != null) {
getLog().info("Layout: " + this.layout);
repackager.setLayout(this.layout.layout());
}
//寻找项目运行时依赖的jar，过滤后
Set<Artifact> artifacts = filterDependencies(this.project.getArtifacts(),
getFilters(getAdditionalFilters()));
//将Artifact转化成Libraries
Libraries libraries = new ArtifactsLibraries(artifacts, this.requiresUnpack,
getLog());
try {
LaunchScript launchScript = getLaunchScript();
//进行repackage
repackager.repackage(target, libraries, launchScript);
}
catch (IOException ex) {
throw new MojoExecutionException(ex.getMessage(), ex);
}
if (this.classifier != null) {
getLog().info("Attaching archive: " + target + ", with classifier: "
+ this.classifier);
this.projectHelper.attachArtifact(this.project, this.project.getPackaging(),
this.classifier, target);
}
else if (!source.equals(target)) {
this.project.getArtifact().setFile(target);
getLog().info("Replacing main artifact " + source + " to " + target);
}
基本上重要的步骤都有注释，应该不难理解的。再来看下面，当然也不是重点，看看就行
public void repackage(File destination, Libraries libraries,
LaunchScript launchScript) throws IOException {
if (destination == null || destination.isDirectory()) {
throw new IllegalArgumentException("Invalid destination");
}
if (libraries == null) {
throw new IllegalArgumentException("Libraries must not be null");
}
if (alreadyRepackaged()) {
return;
}
destination = destination.getAbsoluteFile();
File workingSource = this.source;
//如果源jar与目标jar的文件路径及名称是一致的
if (this.source.equals(destination)) {
//将源jar重新命名为原名称+.original,同时删除原来的源jar
workingSource = new File(this.source.getParentFile(),
this.source.getName() + ".original");
workingSource.delete();
renameFile(this.source, workingSource);
}
destination.delete();
try {
//将源jar变成JarFile
JarFile jarFileSource = new JarFile(workingSource);
try {
repackage(jarFileSource, destination, libraries, launchScript);
}
finally {
jarFileSource.close();
}
}
finally {
if (!this.backupSource && !this.source.equals(workingSource)) {
deleteFile(workingSource);
}
}
}
这一步所做的是清理工作，如果源jar同目标文件路径名称等一致，将源jar重命名，原来的文件删除。为目标文件腾位置。下面的重点来了。
private void repackage(JarFile sourceJar, File destination, Libraries libraries,
LaunchScript launchScript) throws IOException {
JarWriter writer = new JarWriter(destination, launchScript);
try {
final List<Library> unpackLibraries = new ArrayList<Library>();
final List<Library> standardLibraries = new ArrayList<Library>();
libraries.doWithLibraries(new LibraryCallback() {
@Override
public void library(Library library) throws IOException {
File file = library.getFile();
if (isZip(file)) {
if (library.isUnpackRequired()) {
unpackLibraries.add(library);
}
else {
standardLibraries.add(library);
}
}
}
});
//按照规则写入manifest文件
writer.writeManifest(buildManifest(sourceJar));
Set<String> seen = new HashSet<String>();
writeNestedLibraries(unpackLibraries, seen, writer);
//写入源jar中的内容
writer.writeEntries(sourceJar);
//写入标准的jar,依赖的jar
writeNestedLibraries(standardLibraries, seen, writer);
if (this.layout.isExecutable()) {
//写入spring boot loader的类
writer.writeLoaderClasses();
}
}
finally {
try {
writer.close();
}
catch (Exception ex) {
// Ignore
}
}
