java - 使用 lambda 表达式编译代码时出错

Question

我有以下代码:

package com.mongoDB;

import spark.Spark;

public class HelloWorldSparkStyle {
   public static void main(String[] args) {
       Spark.get("/hello", (req, res) -> "Hello World");
   }
}

当我通过 main 方法运行它时它运行良好，但当我尝试编译它时抛出以下错误:

\HelloWorldSparkStyle.java:[9,33] error: lambda expressions are not supported in -source 1.5

D:\WorkspaceWithJava8\BeginnerProject>javac -version
javac 1.8.0_60

我正在使用 Eclipse IDE 并尝试通过命令行编译它。

Answer 1

默认情况下，maven-compiler-plugin 使用 Java 5 编译类。引用 its documentation :

Also note that at present the default source setting is 1.5 and the default target setting is 1.5, independently of the JDK you run Maven with. If you want to change these defaults, you should set source and target as described in Setting the -source and -target of the Java Compiler.

您需要将其配置为使用 Java 8，如下所示:

<plugin>
    <artifactId>maven-compiler-plugin</artifactId>
    <version>3.3</version>
    <configuration>
      <source>1.8</source>
      <target>1.8</target>
    </configuration>
</plugin>