Cannot change version of project facet Dynamic Web Module to 3.1

最近项目一直报错，看的极度的不爽，于是找了很长时间的解决方案。

先说一下环境Spring + SpringMVC + MAVEN + jdk 1.8 + servlet 3.1

由于是web 项目，这里选用了 servlet 3.1 的jar 包，在pom 中引入

<properties>
    <standard.version>1.1.2</standard.version>
    <jstl.version>1.2</jstl.version>
    <servlet-api.verison>3.1.0</servlet-api.verison>
    <jsp-api.version>2.2</jsp-api.version>
</properties>
<dependencies>
    <dependency>
        <groupId>taglibs</groupId>
        <artifactId>standard</artifactId>
        <version>${standard.version}</version>
        <type>jar</type>
    </dependency>
    <dependency>
        <groupId>javax.servlet</groupId>
        <artifactId>jstl</artifactId>
        <version>${jstl.version}</version>
        <type>jar</type>
    </dependency>
    <dependency>
        <groupId>javax.servlet</groupId>
        <artifactId>javax.servlet-api</artifactId>
        <version>${servlet-api.verison}</version>
        <scope>provided</scope>
    </dependency>
    <dependency>
        <groupId>javax.servlet.jsp</groupId>
        <artifactId>jsp-api</artifactId>
        <version>${jsp-api.version}</version>
        <scope>provided</scope>
    </dependency>
</dependencies>

而 web.xml 的头文件也要改为3.1（可以照着 tomcat8 的web.xml 复制这段头文件）

<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee
                     http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"
    version="3.1">

方法一（推荐）：

为了Maven 的编译环境和所设置的jdk 是一致的，在pom 中添加一个编译插件

<build>
        <plugins>
            <!-- Compiler 插件, 设定JDK版本 -->
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.1</version>
                <configuration>
                    <source>1.8</source>
                    <target>1.8</target>
                    <showWarnings>true</showWarnings>
                </configuration>
            </plugin>
        </plugins>
                ……
 
</build>