在android项目中添加第三方jar包虽然不是一个很复杂的问题，但是确实给很多开发者带来了不小的困扰。我自己就曾经碰到过calss not found exception、error inflating class等本质都是第三方jar包未被真正识别但报错指向其他问题的状况，碰到这类问题时我们很容易会被这些指向不够准确的报错误导，因此正确地添加第三方jar包就显得很重要。网上关于这个问题的信息也比较杂乱，因此希望借此文章对这个问题进行明确的解释和解答。
首先要说的是为什么会出现这个问题？我们在以往开发java程序的过程中都已经习惯于通过add external archives来添加第三方的jar包，之所以不能在android项目中用同样的方法引入第三方jar包的原因，下面是来自eclipse j2ee开发者之一Russ Bateman的解释：
I'm an Eclipse JEE developer and have been in the habit for many years of adding third-party libraries via the "User Library" mechanism in Build Path. Of course, there are at least 3 ways to add a third-party library, the one I use is the most elegant, in my humble opinion.
This will not work, however, for Android, whose Dalvik "JVM" cannot handle an ordinary Java-compiled class, but must have it converted to a special format. This does not happen when you add a library in the way I'm wont to do it.
Instead, follow the (widely available) instructions for importing the third-party library, then adding it using Build Path (which makes it known to Eclipse for compilation purposes). Here is the step-by-step:
- Download the library to your host development system.
- Create a new folder, libs, in your Eclipse/Android project.
- Right-click libs and choose Import -> General -> File System, then Next, Browse in the filesystem to find the library's parent directory (i.e.: where you downloaded it to).
- Click OK, then click the directory name (not the checkbox) in the left pane, then check the relevant JAR in the right pane. This puts the library into your project (physically).
- Right-click on your project, choose Build Path -> Configure Build Path, then click the Libraries tab, then Add JARs..., navigate to your new JAR in the libs directory and add it. (This, incidentally, is the moment at which your new JAR is converted for use on Android.)
What you've done here accomplishes two things:
- Includes a Dalvik-converted JAR in your Android project.
- Makes Java definitions available to Eclipse in order to find the third-party classes when developing (that is, compiling) your project's source code.
他的意思是android的dalvik虚拟机不能直接处理编译过的java .class文件，因此直接添加第三方jar包需要经过一定的处理才能被android项目正常识别并使用。以下是他提供的步骤：
- 下载第三方jar包
- 在android项目下创建一个libs目录（就我理解及测试的经验，名称并不固定,你完全可以取其他名称）
- 在eclipse中右键点击libs目录，依次选择Import -> General -> File System,选中jar包所在目录， 然后选中这个目录下的jar包
注：到这一步为止你就成功地把jar包添加到项目中（但是还没有被android的虚拟机识别，因此如果这时你使用jar包中的类，编译都无法通过）
4.右键点击项目名，依次选择Build Path -> Configure Build Path，选择library选项卡。点击右边的add jars，选择libs目录下的jar包
注：这一步就帮助android虚拟机来处理之前添加的jar包
理论上到这一步应该就可以正常使用了，但是如果到这一步你调试还会出错的话可以尝试右键点击libs目录，选择build path –> configure as source folder ，基本上到这一步就可以正常使用第三方jar包，继续你的android开发之旅了