java -jar經常會報兩個錯誤

1. 找不到主類異常

2. 依賴的jar檔案未打入到包中

怎麼解決呢？

1. POM檔案新增maven-compiler-plugin以及maven-assembly-plugin，注意在maven-assembly-plugin中要指定mainClass，這樣可以避免java –jar 時報找不到主類異常。

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>

  <groupId>cn.hfi</groupId>
  <artifactId>itemProcess</artifactId>
  <version>1.0-SNAPSHOT</version>
  <packaging>jar</packaging>

  <name>itemProcess</name>
  <url>http://maven.apache.org</url>

  <properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    <java.version>1.8</java.version>
  </properties>

  <dependencies>
    
  </dependencies>

  <build>
    <finalName>${project.artifactId}</finalName>
    <plugins>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-compiler-plugin</artifactId>
        <version>2.5.1</version>
        <configuration>
          <source>${java.version}</source>
          <target>${java.version}</target>
          <showWarnings>true</showWarnings>
        </configuration>
      </plugin>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-assembly-plugin</artifactId>
        <version>3.1.0</version>
        <configuration>
          <archive>
            <manifest>
              <mainClass>cn.hfi.App</mainClass>
            </manifest>
          </archive>
          <descriptorRefs>
            <descriptorRef>jar-with-dependencies</descriptorRef>
          </descriptorRefs>
        </configuration>
      </plugin>
    </plugins>
  </build>
</project>
 

2. 在intelliij idea的專案terminal中執行mvn compile assembly:single

會進行打包，並將依賴打入到包中

E:\develop_IJ\itemProcess>mvn compile assembly:single
[INFO] Scanning for projects...
[INFO]
[INFO] ------------------------------------------------------------------------
[INFO] Building itemProcess 1.0-SNAPSHOT
[INFO] ------------------------------------------------------------------------
[WARNING] The artifact org.apache.commons:commons-io:jar:1.3.2 has been relocated to commons-io:commons-io:jar:1.3.2
[INFO]
[INFO] --- maven-resources-plugin:2.6:resources (default-resources) @ itemProcess ---
[INFO] Using 'UTF-8' encoding to copy filtered resources.
[INFO] Copying 3 resources
[INFO]
[INFO] --- maven-compiler-plugin:2.5.1:compile (default-compile) @ itemProcess ---
[INFO] Nothing to compile - all classes are up to date
[INFO]
[INFO] --- maven-assembly-plugin:3.1.0:single (default-cli) @ itemProcess ---
[WARNING] While downloading org.apache.commons:commons-io:1.3.2
  This artifact has been relocated to commons-io:commons-io:1.3.2.
  https://issues.sonatype.org/browse/MVNCENTRAL-244


[INFO] Building jar: E:\develop_IJ\itemProcess\target\itemProcess-jar-with-dependencies.jar
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 9.924 s
[INFO] Finished at: 2018-07-30T11:48:16+08:00
[INFO] Final Memory: 35M/516M
[INFO] ------------------------------------------------------------------------
 

3. windows下開啟cmd，cd到jar位置

執行java -jar  itemProcess-jar-with-dependencies.jar

4. 可能存在以下這個需求：一個maven專案中有多個帶main函式的子專案，那麼如何指定生成的某個jar檔案呢？

比如下面這個配置檔案

<build>
<plugins>
<plugin>
<artifactId>maven-assembly-plugin</artifactId>
<version>2.2.1</version>
<executions>
<execution>
<id>make-network-logs-job</id>
<configuration>
<descriptors>
	<descriptor>assembly.xml</descriptor>
</descriptors>
<archive>
	<manifest>
		<mainClass>com.packtpub.esh.nwlogs.Driver</mainClass>
	</manifest>
</archive>
<finalName>${project.artifactId}-${project.version}-nwlogs</finalName>
</configuration>
<phase>package</phase>
<goals>
<goal>single</goal>
</goals>
</execution>
<execution>
<id>make-tweets2es-job</id>
<configuration>
<descriptors>
	<descriptor>assembly.xml</descriptor>
</descriptors>
<archive>
	<manifest>
		<mainClass>com.packtpub.esh.tweets2es.Driver</mainClass>
	</manifest>
</archive>
<finalName>${project.artifactId}-${project.version}-tweets2es</finalName>
</configuration>
<phase>package</phase>
<goals>
<goal>single</goal>
</goals>
</execution>
<execution>
<id>make-tweets2hdfs-job</id>
<configuration>
<descriptors>
	<descriptor>assembly.xml</descriptor>
</descriptors>
<archive>
	<manifest>
		<mainClass>com.packtpub.esh.tweets2hdfs.Driver</mainClass>
	</manifest>
</archive>
<finalName>${project.artifactId}-${project.version}-tweets2hdfs</finalName>
</configuration>
<phase>package</phase>

<goals>
<goal>single</goal>
</goals>

</execution>
<execution>
<id>make-historywords-job</id>
<configuration>
<descriptors>
	<descriptor>assembly.xml</descriptor>
</descriptors>
<archive>
	<manifest>
		<mainClass>com.packtpub.esh.historywords2hdfs.EsToHDFS</mainClass>
	</manifest>
</archive>
<finalName>history2hdfs</finalName>
</configuration>
<phase>package</phase>
<goals>
<goal>single</goal>
</goals>

</execution>
</executions>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.3</version>
<configuration>
<source>1.8</source>
<target>1.8</target>
</configuration>
</plugin>
</plugins>
</build>
 

可以指定mvn compile assembly:[email protected]來執行具體某個execution id的任務

另一種可選的解決方法是使用profile，在這裡有種大材小用的感覺