使用动态依赖项构建多个Java项目

Question

I have multiple java projects in a folder. Also there is a second folder with libraries, that might be used as build dependencies from the projects. The projects may also have dependencies to other Projects. What's the best approach to build all projects ?

In other words I want to build the projects without explicit telling their dependencies.I think the biggest problem is the dependecy between the projects.

Answer 1

There are multiple build systems that are available that you may use. Maven has a complete dependency system built into it. Almost all third party open source jars are directly accessible via the World Wide Maven repository system. Basically, you describe the jar you need (groupId, artifactId, and version) and Maven will automatically fetch it for you. Not only that, but Maven also will build your project without having to create a build file. Instead, you have to describe your project in a project object model (a pom.xml file) and Maven will download everything you need, including all compilers, etc.

Almost all new projects use Maven, but Maven has a few downsides:

• Since you don't control a build process, it can sometimes feel like poking a prodding a black box to get the build to work the way you want.
• Documentation can be scant -- especially if you're moving beyond basic Java compiles.
• You usually have to arrange your project in a specific layout. For example, source files should go under src/main/java while JUnit tests are under src/test/java . You don't have to follow the recommended layout, but then you'd have to modify the pom.xml file this way and that to get your build to work. That defeats the whole purpose of the pom.xml in the first place.
• If you already have another build system setup (like Ant), you lose everything. There's no easy way to move from Ant to Maven.

The other is called Ant with Ivy . Ivy uses Ant for building, but can access Maven's world wide repository system for third party dependencies. It's a great compromise if you already are heavily invested in Ant. I also find Ant with Ivy to be better documented than Maven (although that's not too difficult). There's an excellent chapter going over the basics of Ivy in Manning Publication's Ant in Action .

With either process, I would recommend that you build a company wide Maven repository using either Nexus or Artifactory . This way, any proprietary third party jars (like Oracle jars) can also be stored in your company wide Maven repository since they won't be in the standard World Wide Maven repository.

By the way, if this is a company wide effort, and you are moving multiple Ant projects into Ivy, I have an Ivy project I use in Github that makes things easier.

Oh, there's a third possibility called Gradle which I know nothing about. I also believe it can use the World Wide Maven repository. It's based on Groovy which is based on Java syntax, and that's about all I can say. Maybe others can fill you in on the details. The Gradle group contends it solves a lot of problems of both Ant/Ivy and Maven.

Answer 2

Whatever tool you use, if you have various projects interdependent, you need to be clear on the independent ones which will be built first before building the dependent projects. You need to have a clear dependency structure for your projects.

Answer 3

You can do this with Apache Ivy . You can lay out the locations for you common libraries, define published artifacts and inter-dependencies in an ivy.xml document in each project, and let a top-level Ant build with the Ivy tasks figure out what the build order should be based on those dependencies.