报错分析

报错原因：Maven 构建时，Java 版本配置不匹配

我安装的JDK版本是1.8，但由于种种原因，Maven构建时指定了 Java 17 作为目标发行版，从而导致错误

解决方案

首先，java -version，查看环境变量是否设置为了想要的JDK版本

1.检查pom文件

由于是在Maven构建时报错，所以优先检查pom文件，查看是否在properties中设置了错误的compiler.source或compiler.target：

如上所示则是正确的（因为使用的JDK版本是1.8）

两个参数的含义分别是：

maven.compiler.source设置为 1.8，表示使用 Java 8 的语法规则来编译源代码

maven.compiler.target设置为 1.8，表示生成的字节码版本为 Java 8

2.查看Maven的有效配置

在编译时，可以使用 maven-compiler-plugin 插件指定所使用的JDK的版本，如果没有指定的话，将会使用默认配置，可以通过mvn help:effective-pom指令来查看默认配置，打印输出的内容结构如下：

  <modelVersion>4.0.0</modelVersion>
  <groupId>com.why</groupId>
  <artifactId>Sort-Array-Desc</artifactId>
  <version>1.0-SNAPSHOT</version>
  <properties>
    <maven.compiler.compilerVersion>17</maven.compiler.compilerVersion>
    <maven.compiler.source>17</maven.compiler.source>
    <maven.compiler.target>17</maven.compiler.target>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
  </properties>
  <dependencies>
    <dependency>
      <groupId>org.apache.hive</groupId>
      <artifactId>hive-exec</artifactId>
      <version>3.1.3</version>
      <scope>compile</scope>
    </dependency>
  </dependencies>
  <repositories>
    <repository>
      <snapshots>
        <enabled>false</enabled>
      </snapshots>
      <id>central</id>
      <name>Central Repository</name>
      <url>https://repo.maven.apache.org/maven2</url>
    </repository>
  </repositories>
  <pluginRepositories>
    <pluginRepository>
      <releases>
        <updatePolicy>never</updatePolicy>
      </releases>
      <snapshots>
        <enabled>false</enabled>
      </snapshots>
      <id>central</id>
      <name>Central Repository</name>
      <url>https://repo.maven.apache.org/maven2</url>
    </pluginRepository>
  </pluginRepositories>
  <build>
    <sourceDirectory>D:\codes\java\hive\Sort-Array-Desc\src\main\java</sourceDirectory>
    <scriptSourceDirectory>D:\codes\java\hive\Sort-Array-Desc\src\main\scripts</scriptSourceDirectory>
    <testSourceDirectory>D:\codes\java\hive\Sort-Array-Desc\src\test\java</testSourceDirectory>
    <outputDirectory>D:\codes\java\hive\Sort-Array-Desc\target\classes</outputDirectory>
    <testOutputDirectory>D:\codes\java\hive\Sort-Array-Desc\target\test-classes</testOutputDirectory>
    <resources>
      <resource>
        <directory>D:\codes\java\hive\Sort-Array-Desc\src\main\resources</directory>
      </resource>
    </resources>
    <testResources>
      <testResource>
        <directory>D:\codes\java\hive\Sort-Array-Desc\src\test\resources</directory>
      </testResource>
    </testResources>
    <directory>D:\codes\java\hive\Sort-Array-Desc\target</directory>
    <finalName>Sort-Array-Desc</finalName>
    <pluginManagement>
      <plugins>
        <plugin>
          <artifactId>maven-antrun-plugin</artifactId>
          <version>1.3</version>
        </plugin>
        <plugin>
          <artifactId>maven-assembly-plugin</artifactId>
          <version>2.2-beta-5</version>
        </plugin>
        <plugin>
          <artifactId>maven-dependency-plugin</artifactId>
          <version>2.8</version>
        </plugin>
        <plugin>
          <artifactId>maven-release-plugin</artifactId>
          <version>2.5.3</version>
        </plugin>
      </plugins>
    </pluginManagement>
    <plugins>
      <plugin>
        <artifactId>maven-compiler-plugin</artifactId>
        <version>3.8.1</version>
        <executions>
          <execution>
            <id>default-compile</id>
            <phase>compile</phase>
            <goals>
              <goal>compile</goal>
            </goals>
            <configuration>
              <source>1.8</source>
              <target>1.8</target>
            </configuration>
          </execution>
          <execution>
            <id>default-testCompile</id>
            <phase>test-compile</phase>
            <goals>
              <goal>testCompile</goal>
            </goals>
            <configuration>
              <source>1.8</source>
              <target>1.8</target>
            </configuration>
          </execution>
        </executions>
        <configuration>
          <source>1.8</source>
          <target>1.8</target>
        </configuration>
      </plugin>
      <plugin>
        <artifactId>maven-clean-plugin</artifactId>
        <version>2.5</version>
        <executions>
          <execution>
            <id>default-clean</id>
            <phase>clean</phase>
            <goals>
              <goal>clean</goal>
            </goals>
          </execution>
        </executions>
      </plugin>
      <plugin>
        <artifactId>maven-resources-plugin</artifactId>
        <version>2.6</version>
        <executions>
          <execution>
            <id>default-testResources</id>
            <phase>process-test-resources</phase>
            <goals>
              <goal>testResources</goal>
            </goals>
          </execution>
          <execution>
            <id>default-resources</id>
            <phase>process-resources</phase>
            <goals>
              <goal>resources</goal>
            </goals>
          </execution>
        </executions>
      </plugin>
      <plugin>
        <artifactId>maven-jar-plugin</artifactId>
        <version>2.4</version>
        <executions>
          <execution>
            <id>default-jar</id>
            <phase>package</phase>
            <goals>
              <goal>jar</goal>
            </goals>
          </execution>
        </executions>
      </plugin>
      <plugin>
        <artifactId>maven-surefire-plugin</artifactId>
        <version>2.12.4</version>
        <executions>
          <execution>
            <id>default-test</id>
            <phase>test</phase>
            <goals>
              <goal>test</goal>
            </goals>
          </execution>
        </executions>
      </plugin>
      <plugin>
        <artifactId>maven-install-plugin</artifactId>
        <version>2.4</version>
        <executions>
          <execution>
            <id>default-install</id>
            <phase>install</phase>
            <goals>
              <goal>install</goal>
            </goals>
          </execution>
        </executions>
      </plugin>
      <plugin>
        <artifactId>maven-deploy-plugin</artifactId>
        <version>2.7</version>
        <executions>
          <execution>
            <id>default-deploy</id>
            <phase>deploy</phase>
            <goals>
              <goal>deploy</goal>
            </goals>
          </execution>
        </executions>
      </plugin>
      <plugin>
        <artifactId>maven-site-plugin</artifactId>
        <version>3.3</version>
        <executions>
          <execution>
            <id>default-site</id>
            <phase>site</phase>
            <goals>
              <goal>site</goal>
            </goals>
            <configuration>
              <outputDirectory>D:\codes\java\hive\Sort-Array-Desc\target\site</outputDirectory>
              <reportPlugins>
                <reportPlugin>
                  <groupId>org.apache.maven.plugins</groupId>
                  <artifactId>maven-project-info-reports-plugin</artifactId>
                </reportPlugin>
              </reportPlugins>
            </configuration>
          </execution>
          <execution>
            <id>default-deploy</id>
            <phase>site-deploy</phase>
            <goals>
              <goal>deploy</goal>
            </goals>
            <configuration>
              <outputDirectory>D:\codes\java\hive\Sort-Array-Desc\target\site</outputDirectory>
              <reportPlugins>
                <reportPlugin>
                  <groupId>org.apache.maven.plugins</groupId>
                  <artifactId>maven-project-info-reports-plugin</artifactId>
                </reportPlugin>
              </reportPlugins>
            </configuration>
          </execution>
        </executions>
        <configuration>
          <outputDirectory>D:\codes\java\hive\Sort-Array-Desc\target\site</outputDirectory>
          <reportPlugins>
            <reportPlugin>
              <groupId>org.apache.maven.plugins</groupId>
              <artifactId>maven-project-info-reports-plugin</artifactId>
            </reportPlugin>
          </reportPlugins>
        </configuration>
      </plugin>
    </plugins>
  </build>
  <reporting>
    <outputDirectory>D:\codes\java\hive\Sort-Array-Desc\target\site</outputDirectory>
  </reporting>
</project>

可以看到，默认配置中，指定了源代码编译的语法规则以及生成的字节码文件版本都是Java 17，与我们本地的环境不符，因此·会报错：无效的目标发行版17

此时我很奇怪为什么默认会用Java 17的语法去进行编译，于是去查看maven的配置文件settings.xml，结果发现在<profiles></profiles>中添加了一个profile：

可能是之前想要控制maven的默认编译行为，结果忘记了😂

所以解决方案有两种，第一种就是删除这里的配置，由于我所使用的maven版本是3.6.3，默认就是用Java 8 进行编译了：

第二种方法就是使用maven-compiler-plugin插件配置：

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.8.1</version>
                <configuration>
                    <source>1.8</source>
                    <target>1.8</target>
                </configuration>
            </plugin>
        </plugins>
    </build>

从而覆盖默认的配置

3.检查IDE中的JDK 配置

除了以上Maven配置的问题，我们也需要检查IDE中的配置，下述的方法在运行代码报错时同样可用

3.1 Project Structure

进入File -> Project Structure

在Project标签页中，检查 Project SDK 是否设置为 1.8：

在 Modules 标签页中，检查 Module SDK以及language level是否设置为 1.8：

3.2 Java Compiler

进入File -> Settings -> Java Compiler，检查Target bytecode version是否设置为1…8：