安装了Java11后，用其编译多个Springboot工程，老是失败，后来发现所有工程指定了java版本为java8，于是乎卸载了java11，安装了java8，再去编译。

其中某个工程在之前用java11编译的时候没有任何问题， 但是换成java8后出现了以下错误：

具体信息： 

F:\Digital marketing\workspace-scrm\workspace-scrm\wit-gateway-app>mvn clean install package -Dmaven.test.skip=true
[INFO] Scanning for projects...
Downloading from nexus: http://......:8051/repository/maven-public/net/trueland/tcloud/scrm/common-dependencies/3.1-SNAPSHOT/maven-metadata.xml
Downloaded from nexus: http://......:8051/repository/maven-public/net/trueland/tcloud/scrm/common-dependencies/3.1-SNAPSHOT/maven-metadata.xml (621 B at 3.8 kB/s)
[INFO]
[INFO] --------------< net.trueland.tcloud.scrm:tcloud-gateway >---------------
[INFO] Building tcloud-gateway 3.1.0
[INFO] --------------------------------[ jar ]---------------------------------
Downloading from nexus: http://......:8051/repository/maven-public/net/trueland/commons/1.1-SNAPSHOT/maven-metadata.xml
Downloaded from nexus: http://......:8051/repository/maven-public/net/trueland/commons/1.1-SNAPSHOT/maven-metadata.xml (983 B at 16 kB/s)
Downloading from nexus: http://......:8051/repository/maven-public/net/trueland/tcloud/scrm/common-base/3.1-SNAPSHOT/maven-metadata.xml
Downloaded from nexus: http://......:8051/repository/maven-public/net/trueland/tcloud/scrm/common-base/3.1-SNAPSHOT/maven-metadata.xml (996 B at 15 kB/s)
[INFO]
[INFO] --- maven-clean-plugin:3.1.0:clean (default-clean) @ tcloud-gateway ---
[INFO] Deleting F:\Digital marketing\wit-gateway-app\target
[INFO]
[INFO] --- maven-resources-plugin:3.2.0:resources (default-resources) @ tcloud-gateway ---
[INFO] Using 'UTF-8' encoding to copy filtered resources.
[INFO] Using 'UTF-8' encoding to copy filtered properties files.
[INFO] Copying 0 resource
[INFO] Copying 6 resources
[INFO]
[INFO] --- maven-compiler-plugin:3.8.1:compile (default-compile) @ tcloud-gateway ---
[INFO] Changes detected - recompiling the module!
[INFO] Compiling 14 source files to F:\Digital marketing\workspace-scrm\wit-gateway-app\target\classes
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  2.305 s
[INFO] Finished at: 2022-01-12T08:43:21+08:00
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.8.1:compile (default-compile) on project tcloud-gateway: Fatal error compiling: 无效的目标发行版: 11 -> [Help 1]
[ERROR]
[ERROR] To see the full stack trace of the errors, re-run Maven with the -e switch.
[ERROR] Re-run Maven using the -X switch to enable full debug logging.
[ERROR]
[ERROR] For more information about the errors and possible solutions, please read the following articles:
[ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/MojoExecutionException

从网上查了查资料，需要指定Maven的java编译器版本：

1. 在Java 8和更早版本中指定Maven的Java编译器

在Java 8 和更早版本开始，可以通过两种方式在Maven POM文件中设置Java编译器版本：

• 通过Maven Java编译器属性。
• 通过Maven Java编译器插件。

下面将具体说明这两种在Maven中设置Java编译器版本的方法。

1. Maven Java编译器属性

最简单的方法是通过Maven Java编译器属性。

在我们工程的pom.xml文件中进行设置，这些属性必须包含在POM文件的properties元素中。

<properties>
  <maven.compiler.target>1.8</maven.compiler.target>
  <maven.compiler.source>1.8</maven.compiler.source>
</properties>

下面是一个具体的例子：

<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>com.bruce</groupId>
    <artifactId>wit-example</artifactId>
    <version>0.1.0</version>
    <packaging>jar</packaging>
    
    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <maven.compiler.target>1.8</maven.compiler.target>
        <maven.compiler.source>1.8</maven.compiler.source>
    </properties>
    
    <dependencies>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
            <scope>test</scope>
        </dependency>
    </dependencies>
</project>

 2.Maven Java编译器插件

第二种方式是通过插件：

<build>
  <plugins>
    <plugin>
      <groupId>org.apache.maven.plugins</groupId>
      <artifactId>maven-compiler-plugin</artifactId>
      <version>3.6.1</version>
      <configuration>
        <source>1.8</source>
        <target>1.8</target>
      </configuration>
    </plugin>
  </plugins>
</build>

下面是一个具体的例子：

<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>com.bruce</groupId>
    <artifactId>wit-example</artifactId>
    <version>0.1.0</version>
    <packaging>jar</packaging>

    <dependencies>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
            <scope>test</scope>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.6.1</version>
                <configuration>
                    <source>1.8</source>
                    <target>1.8</target>
                </configuration>
            </plugin>
        </plugins>
    </build>
</project>

 

2. 在Java 9及以后的版本中指定Maven的Java编译器

在Java 9和更高版本中，也要使用插件，但是要用release属性来代替source和target属性。

<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-compiler-plugin</artifactId>
    <version>3.8.0</version>
    <configuration>
        <release>11</release>
    </configuration>
</plugin>

Note: Maven Java编译器插件的版本已从3.6.1更改为3.8.0