jar包读取资源文件报错：找不到资源文件(No such file or directory)

1、遇到问题

（1）Maven项目开发阶段正常运行，Java程序可以读取配置文件

public class Main {

    public static void main(String[] args) throws Exception {

        Main.readFile("resources/sharepointApp.xml");
    }

    public static byte[] readFile(String fileName) throws Exception {
        String path = SharepointApp.class.getClassLoader().getResource(fileName).getPath();
        System.out.println(path);
        File file = new File(path);
        byte[] buf = new byte[(int) file.length()];
        InputStream input=new FileInputStream(fileName);
        input.read(buf);
        input.close();
        return buf;
    }
}

（2）但是，Maven项目打成jar包后，放到服务器上运行时，却报错，找不到配置文件。

[[email protected] ~]# java -jar webservice-0.0.1-SNAPSHOT-jar-with-dependencies.jar 
file:/root/webservice-0.0.1-SNAPSHOT-jar-with-dependencies.jar!/resources/sharepointApp.xml
Exception in thread "main" java.io.FileNotFoundException: file:/root/webservice-0.0.1-SNAPSHOT-jar-with-dependencies.jar!/resources/sharepointApp.xml (No such file or directory)
    at java.io.FileInputStream.open0(Native Method)
    at java.io.FileInputStream.open(FileInputStream.java:195)
    at java.io.FileInputStream.<init>(FileInputStream.java:138)
    at java.io.FileInputStream.<init>(FileInputStream.java:93)
    at com.cntaiping.tpa.webservice.SharepointApp.readFile(SharepointApp.java:53)
    at com.cntaiping.tpa.webservice.SharepointApp.sendSms(SharepointApp.java:30)
    at Main.main(Main.java:22)
[[email protected] ~]#

（3）查看jar结构，对应配置文件存在。

[[email protected] ~]# jar tf webservice-0.0.1-SNAPSHOT-jar-with-dependencies.jar
。。。
DownloadDemo.class
Main.class
META-INF/maven/cn.hadron/webservice/pom.properties
META-INF/maven/cn.hadron/webservice/pom.xml
resources/a.xml
resources/result.xml
resources/sharepoint.xml
resources/sharepointApp.xml
resources/table.xml
Test.class
META-INF/maven/commons-io/
META-INF/maven/commons-codec/
META-INF/maven/commons-codec/commons-codec/
META-INF/maven/commons-io/commons-io/
META-INF/maven/commons-logging/
META-INF/maven/com.github.virtuald/
META-INF/maven/com.github.virtuald/curvesapi/
META-INF/maven/commons-logging/commons-logging/
[[email protected] ~]#

2、问题分析

由上面运行jar包输出/root/webservice-0.0.1-SNAPSHOT-jar-with-dependencies.jar!/resources/sharepointApp.xml可知，该值是我们通过自定义方法readFile()读取的文件路径，显然这个值不是一般意义上的URL地址。所以jar包中的类源代码用File f=new File(项目内地址)的形式，是不可能定位到文件资源的。

3、解决办法

jar中资源有其专门的URL形式：jar:<url>!/{entry}
可以通过Class类的getResourceAsStream()方法来获取资源文件输入流方式读取文件。

public class FileUtil {
    /**
     * 读取配置文件
     * @return
     */
    public static byte[] readConfigFile(String cfgFile) {
        try {
            InputStream in=FileUtil.class.getClassLoader().getResource(cfgFile).openStream();
            BufferedReader br=new BufferedReader(new InputStreamReader(in));
            StringBuilder sb=new StringBuilder();        
            String line="";
            while((line=br.readLine())!=null) {
                sb.append(line);
            }
            return sb.toString().getBytes();
        } catch (IOException e) {
            e.printStackTrace();
            return null;
        }
    }

    //省略其他的方法

    //主方法
    public static void main(String[] args) throws IOException {
         byte[] buf = FileUtil.readConfigFile("resources/sharepointApp.xml");

    }
}