有没有办法从本地 jar 在 pom 文件中创建 maven 依赖项

Question

There is a java project which has too many jar files and it has become difficult to manage all of them. I know there is a way to convert this project to a maven project but I don't want to manually add the dependency for each jar in my project to the pom file.

Is there any way to create the pom file using the local jar files such that the pom will contain the dependency tag for each jar.

Edit: I want to clarify that I do not want to add the jars from/to the local repository. The local repository approach will not work for me as the project will be used by multiple users across different systems.

I wanted to create regular pom dependency entries along with groupId, artifactId and version for the jar files which I already have so that I can copy-paste it into the pom file when I convert my project to a Maven project. As I have a large number of JARs in my project, I would have to do it all manually.

Solution provided by @Milen Dyankov worked for me. I was able to get the information I needed from most of the JAR files.

Answer 1

This code

    public static void main(String[] args) throws IOException {
        Set<String> missingMavenData = new HashSet<String>();
        String FOLDER = "/path/to/your/folder/with/jars";
        
        Files
         .walk(Paths.get(FOLDER), FileVisitOption.FOLLOW_LINKS)
         .map(Path::toFile)
         .filter(f -> f.isFile())
         .filter(f -> f.getName().endsWith(".jar"))
         .map(f -> {
            try {
                return new JarFile(f);
            } catch (IOException e) {
                e.printStackTrace();
                return null;
            }
         })
         .filter(Objects::nonNull)
         .map(jar -> {
             Properties properties = null;
             Enumeration<JarEntry> entries = jar.entries();
             while (entries.hasMoreElements()) {
                 JarEntry jarEntry = entries.nextElement();
                 if (jarEntry.getName().matches("^META-INF/maven/.*/pom\\.properties$")) {
                     try {
                         properties = new Properties();
                         properties.load(jar.getInputStream(jarEntry));
                         break;
                     } catch (IOException e) {
                         e.printStackTrace();
                     }
                 };
             } 
             if (properties == null) {
                 missingMavenData.add(jar.getName());
             }
             return properties;
         })
         .filter(Objects::nonNull)
         .forEach(properties -> {
            System.out.println("< dependency>");
            System.out.println("    <groupId>" + properties.getProperty("groupId")+ "</groupId>");
            System.out.println("    <artifactId>" + properties.getProperty("artifactId")+ "</artifactId>");
            System.out.println("    <version>" + properties.getProperty("version")+ "</version>");
            System.out.println("</dependency>");
         });
        
        System.out.println("Those JAR files do not contain Maven metadata:");
        missingMavenData.forEach(System.out::println);
    }

will iterate over your jar files and try to find the Maven metadata in them. It will generate the POM entries for those who have it and will list those that don't have it so you can add it manually. I hope this helps.

UPDATE:

I added bom-helper:fromJars goal to BOM Helper Maven Plugin which does more or less the same thing as the above code. One can now simply add the plugin

<plugin>
    <groupId>com.commsen.maven</groupId>
    <artifactId>bom-helper-maven-plugin</artifactId>
    <version>0.2.0</version>
</plugin>

and configure it to call fromJars goal. It can also be called form command line. For example:

mvn bom-helper:fromJars \
 -Dbom-helper.jarsFolder=/path/to/folder/with/jars \
 -Dbom-helper.inplace=true \
 -Dbom-helper.recursive

will update current pom with entries for all jars that have Maven metadata in them.

Answer 2

You can Install manually the JAR into your local Maven repository

First Way

Follow the steps here

mvn install:install-file -Dfile=<path-to-file>

And in here you can be able to add these information in command line

mvn install:install-file -Dfile=<path-to-file> -DgroupId=<group-id> -DartifactId=<artifact-id> -Dversion=<version>

<path-to-file> mentioned path to the JAR to install

<group-id> mentioned group id of the JAR to install

<artifact-id> mentioned artifact id of the JAR to install

<version> mentioned version of the JAR

Second Way

You can create a different local Maven repository

Follow the Steps

we can consider the new local Maven repository is named maven-repository and is located in ${basedir} (the directory containing pom.xml).

Deploying the local JARs in the new local maven repository as below i am following

mvn deploy:deploy-file -Dfile=<path-to-file> -DgroupId=<group-id> -DartifactId=<artifact-id> -Dversion=<version> -Dpackaging=jar -Durl=file:./maven-repository/ -DrepositoryId=maven-repository -DupdateReleaseInfo=true

you can see which the maven deploy:deploy-file installs the artifact in a remote repository but in here repository is located in the local machine

After installing the JARs your need to add the repository in your pom.xml file

<repositories>
    <repository>
        <id>maven-repository</id>
        <url>file:///${project.basedir}/maven-repository</url>
    </repository>
</repositories>

Answer 3

AFAIK there is not Maven way to do this.

You could write a script that computes the SHA1 value of each jar and searches for the jar in your Maven repository. It could, alternatively, open the jars and search for the pom.properties to extract the Maven coordinates.

In any way, this is probably too much programming effort unless you need to do it for many projects.

Answer 4

What you need is your local maven nexus that is only available in your server. Considering you have jars that are only available to you, I guess that you have sources for them. As a result, you should be able to convert them into maven projects and deploy them into your local nexus. After fixing the structure, maven will download your dependencies and the dependencies' dependencies when resolving a project.

Or you could use <scope>system</scope> , but that requires absolute paths and is generally not suggested.