解决项目报错Cannot change version of project facet Dynamic web module to 3.0

1、web.xml文件中约束空间：

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
        xmlns="http://java.sun.com/xml/ns/javaee" 
        xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" 
        id="WebApp_ID" version="3.0">

2、pom.xml引入编译插件，强制指定字符编码集和jdk版本：

<plugins>
        <!-- 编译插件，前置指定当前工程编译锁使用的字符编码集和jdk版本 -->
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-compiler-plugin</artifactId>
            <version>2.3.2</version>
            <configuration>
                <encoding>UTF-8</encoding>
                <source>1.7</source>  
                <target>1.7</target>  
            </configuration>  
        </plugin>
    </plugins>

3、修改org.eclipse.wst.common.project.facet.core.xml

<?xml version="1.0" encoding="UTF-8"?>
<faceted-project>
  <fixed facet="wst.jsdt.web"/>
  <installed facet="jst.web" version="3.0"/>
  <installed facet="wst.jsdt.web" version="1.0"/>
  <installed facet="java" version="1.7"/>
</faceted-project>

重新Maven --> Update Project..