java - 为什么maven编译失败？

Question

我正在尝试使用 Maven 构建一个 Java 项目。我通过 mvn -v 检查 maven 命令，它给出了以下输出

Apache Maven 3.3.9 (bb52d8502b132ec0a5a3f4c09453c07478323dc5; 2015-11-10T18:41:47+02:00)
Maven home: C:\Program Files\Apache\Maven\apache-maven-3.3.9\bin\..
Java version: 1.8.0_101, vendor: Oracle Corporation
Java home: C:\Program Files\Java\jdk1.8.0_101\jre
Default locale: en_US, platform encoding: Cp1252
OS name: "windows 10", version: "10.0", arch: "amd64", family: "dos"

我将 org.joda.time.LocalTime 添加到 HelloWorld.java 如下

package hello;

import org.joda.time.LocalTime;

public class HelloWorld {
    public static void main(String[] args) {
        LocalTime currentTime = new LocalTime();
        System.out.println("The current local time is: " + currentTime);
        Greeter greeter = new Greeter();
        System.out.println(greeter.sayHello());
    }
}

因此，我将 joda-time 依赖项添加到我的 pom.xml 中。这是我的 pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<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/maven-v4_0_0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>org.springframework</groupId>
    <artifactId>gs-maven</artifactId>
    <packaging>jar</packaging>
    <version>0.1.0</version>

    <dependencies>
        <!-- tag::joda[] -->
        <dependency>
            <groupId>joda-time</groupId>
            <artifactId>joda-time</artifactId>
            <version>2.2</version>
        </dependency>
        <!-- end::joda[] -->
        <!-- tag::junit[] -->
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
            <scope>test</scope>
        </dependency>
        <!-- end::junit[] -->
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-shade-plugin</artifactId>
                <version>2.1</version>
                <executions>
                    <execution>
                        <phase>package</phase>
                        <goals>
                            <goal>shade</goal>
                        </goals>
                        <configuration>
                            <transformers>
                                <transformer implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">
                                    <mainClass>hello.HelloWorld</mainClass>
                                </transformer>
                            </transformers>
                        </configuration>
                    </execution>
                </executions>
            </plugin>
        </plugins>
    </build>

</project>

每当我要运行 mvn compile 时，它都会给出输出

[INFO] Scanning for projects...
[INFO]
[INFO] ------------------------------------------------------------------------
[INFO] Building gs-maven 0.1.0
[INFO] ------------------------------------------------------------------------
[INFO]
[INFO] --- maven-resources-plugin:2.6:resources (default-resources) @ gs-maven ---
[WARNING] Using platform encoding (Cp1252 actually) to copy filtered resources, i.e. build is platform dependent!
[INFO] skip non existing resourceDirectory H:\Projects\JAVA\web\unzipped\gs-maven\initial\src\main\resources
[INFO]
[INFO] --- maven-compiler-plugin:3.1:compile (default-compile) @ gs-maven ---
[INFO] Changes detected - recompiling the module!
[WARNING] File encoding has not been set, using platform encoding Cp1252, i.e. build is platform dependent!
[INFO] Compiling 2 source files to H:\Projects\JAVA\web\unzipped\gs-maven\initial\target\classes
[INFO] -------------------------------------------------------------
[ERROR] COMPILATION ERROR :
[INFO] -------------------------------------------------------------
[ERROR] /H:/Projects/JAVA/web/unzipped/gs-maven/initial/src/main/java/hello/HelloWorld.java:[3,21] package org.joda.time does not exist
[ERROR] /H:/Projects/JAVA/web/unzipped/gs-maven/initial/src/main/java/hello/HelloWorld.java:[7,9] cannot find symbol
  symbol:   class LocalTime
  location: class hello.HelloWorld
[ERROR] /H:/Projects/JAVA/web/unzipped/gs-maven/initial/src/main/java/hello/HelloWorld.java:[7,37] cannot find symbol
  symbol:   class LocalTime
  location: class hello.HelloWorld
[INFO] 3 errors
[INFO] -------------------------------------------------------------
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 2.647 s
[INFO] Finished at: 2016-10-03T09:11:07+03:00
[INFO] Final Memory: 14M/114M
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.1:compile (default-compile) on project gs-maven: Compilation failure: Compilation failure:
[ERROR] /H:/Projects/JAVA/web/unzipped/gs-maven/initial/src/main/java/hello/HelloWorld.java:[3,21] package org.joda.time does not exist
[ERROR] /H:/Projects/JAVA/web/unzipped/gs-maven/initial/src/main/java/hello/HelloWorld.java:[7,9] cannot find symbol
[ERROR] symbol:   class LocalTime
[ERROR] location: class hello.HelloWorld
[ERROR] /H:/Projects/JAVA/web/unzipped/gs-maven/initial/src/main/java/hello/HelloWorld.java:[7,37] cannot find symbol
[ERROR] symbol:   class LocalTime
[ERROR] location: class hello.HelloWorld
[ERROR] -> [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/MojoFailureException

请告诉我我做错了什么。

注意:我只是关注 Building Java Projects with Maven作为初学者的教程。

Answer 1

您的 Maven 读取的 Java 版本为 1.8.0_101，而 pom.xml 未更新

1) 尝试安装所需的版本。将JAVA_HOME和pom.xml更新到相同的jdk安装路径

2) mvn clean install - 它的作用是清除您拥有的所有已编译文件，确保您确实是从头开始编译每个模块。