如你所见，Gradle是一个通用的构建工具。你在构建脚本中实现的几乎任何内容它都能够构建。它开箱即用，但是需要你在构建脚本中先写好代码。
As we have seen, Gradle is a general-purpose build tool. It can build pretty much anything you care to implement in your build script. Out-of-the-box, however, it doesn't build anything unless you add code to your build script to do so.

大部分的Java项目的基本流程都是类似的：编译Java源文件，运行单元测试，创建一个Jar包。 如果可以不用为每个项目都去编写这些流程那就好了。在实际上，我们确实不用。Gradle通过 插件来解决这一问题。插件就是Gradle的扩展，可以让你以某种方式来配置你的项目，通常通过添加一些预先配置的任务来共同做一些有用的事情。Gradle内置了许多插件，并且你也可以轻松地编写你自己的插件和分享自己的插件。Java plugin是其中之一，这一插件向项目添加一些编译和测试Java源代码，并打包成JAR包的任务。 
Most Java projects are pretty similar as far as the basics go: you need to compile your Java source files, run some unit tests, and create a JAR file containing your classes. It would be nice if you didn't have to code all this up for every project. Luckily, you don't have to. Gradle solves this problem through the use of plugins. A plugin is an extension to Gradle which configures your project in some way, typically by adding some pre-configured tasks which together do something useful. Gradle ships with a number of plugins, and you can easily write your own and share them with others. One such plugin is the Java plugin. This plugin adds some tasks to your project which will compile and unit test your Java source code, and bundle it into a JAR file.

这个Java插件是基于约定的。这也意味着它为项目的很多个方面都定义了一些默认值，比如Java源文件的位置。如果你遵循这些约定，那么你就不用在构建脚本中再去做太多的事情。如果你不想或无法遵循约定，Gradle也允许你进行自定义。实际上，由于对Java项目的支持是以插件的形式来实现的，你甚至可以完全不用这个构建来构建Java项目。 
The Java plugin is convention based. This means that the plugin defines default values for many aspects of the project, such as where the Java source files are located. If you follow the convention in your project, you generally don't need to do much in your build script to get a useful build. Gradle allows you to customize your project if you don't want to or cannot follow the convention in some way. In fact, because support for Java projects is implemented as a plugin, you don't have to use the plugin at all to build a Java project, if you don't want to.

在后续章节中，我们有深入介绍与Java插件，依赖管理以及多项目构建的相关的许多例子。在本章里，我们还是先了解一下使用Java插件来构建Java项目的基本用法。 
We have in-depth coverage with many examples about the Java plugin, dependency management and multi-project builds in later chapters. In this chapter we want to give you an initial idea of how to use the Java plugin to build a Java project.

让我们来看一个简单的例子。要使用Java插件，只需在构建脚本中添加如下代码：
Let's look at a simple example. To use the Java plugin, add the following to your build file:

apply plugin: 'java'

定义一个Java项目只需要这些就够了。它将会向你的项目应用Java插件，从而添加一些任务。
This is all you need to define a Java project. This will apply the Java plugin to your project, which adds a number of tasks to your project.

Gradle会在 src/main/java and your test source code under和 src/test/java能分别找你的生产 源码和测试源码。并且，在 src/main/resources的所有文件都会作为资源被打包进JAR包，任何在 src/test/resources下的资源文件都会被包含到类路径中用于执行测试。所有输出的文件都会在 build 目录里创建，而JAR包会被输出在build/libs 目录里。 
Gradle expects to find your production source code under src/main/java and your test source code under src/test/java. In addition, any files under src/main/resources will be included in the JAR file as resources, and any files under src/test/resources will be included in the classpath used to run the tests. All output files are created under the build directory, with the JAR file ending up in the build/libs directory.

> gradle build
:compileJava
:processResources
:classes
:jar
:assemble
:compileTestJava
:processTestResources
:testClasses
:test
:check
:build

BUILD SUCCESSFUL

Total time: 1 secs

repositories {
    mavenCentral()
}

dependencies {
    compile group: 'commons-collections', name: 'commons-collections', version: '3.2'
    testCompile group: 'junit', name: 'junit', version: '4.+'
}