配置maven时常见的小问题
1.出现报错Unable to compile class for JSP
报错信息图片如下:

解决方案
1.考虑是否是jar包冲突而出现的问题
在pom.xml中添加jar包没有加限制,如下列代码:
<?xml version="1.0" encoding="UTF-8"?>
<!--修改前-->
<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>org.example</groupId>
<artifactId>maven_web</artifactId>
<version>1.0-SNAPSHOT</version>
<packaging>war</packaging>
<name>maven_web Maven Webapp</name>
<!-- FIXME change it to the project's website -->
<url>http://www.example.com</url>
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<maven.compiler.source>1.7</maven.compiler.source>
<maven.compiler.target>1.7</maven.compiler.target>
</properties>
<dependencies>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.11</version>
<scope>test</scope>
</dependency>
<dependency>
<groupId>javax.servlet</groupId>
<artifactId>servlet-api</artifactId>
<version>2.5</version>
</dependency>
<dependency>
<groupId>javax.servlet.jsp</groupId>
<artifactId>jsp-api</artifactId>
<version>2.0</version>
</dependency>
</dependencies>
</project>
我们需要在servlet-api以及jsp.api的pom依赖后加上provided,使其不参与代码运行,从而避免jar包冲突。具体代码如下所示。
<?xml version="1.0" encoding="UTF-8"?>
<!--修改后-->
<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>org.example</groupId>
<artifactId>maven_web</artifactId>
<version>1.0-SNAPSHOT</version>
<packaging>war</packaging>
<name>maven_web Maven Webapp</name>
<!-- FIXME change it to the project's website -->
<url>http://www.example.com</url>
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<maven.compiler.source>1.7</maven.compiler.source>
<maven.compiler.target>1.7</maven.compiler.target>
</properties>
<dependencies>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.11</version>
<scope>test</scope>
</dependency>
<dependency>
<groupId>javax.servlet</groupId>
<artifactId>servlet-api</artifactId>
<version>2.5</version>
<scope>provided</scope>
</dependency>
<dependency>
<groupId>javax.servlet.jsp</groupId>
<artifactId>jsp-api</artifactId>
<version>2.0</version>
<scope>provided</scope>
</dependency>
</dependencies>
</project>
2.如果解决了jar包还是报错Unable to compile class for JSP,那应该考虑是不是Tomcat版本不兼容项目使用的JRE版本
maven中自带的Tomcat版本是Tomcat6.0.29,而项目中使用的JRE版本为1.8,可能出现不兼容的问题,我们可以在pom.xml中添加依赖使用更高版本的Tomcat,如下所示
<?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/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>org.example</groupId>
<artifactId>maven_web</artifactId>
<version>1.0-SNAPSHOT</version>
<packaging>war</packaging>
<name>maven_web Maven Webapp</name>
<!-- FIXME change it to the project's website -->
<url>http://www.example.com</url>
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<maven.compiler.source>1.7</maven.compiler.source>
<maven.compiler.target>1.7</maven.compiler.target>
</properties>
<dependencies>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.11</version>
<scope>test</scope>
</dependency>
<dependency>
<groupId>javax.servlet</groupId>
<artifactId>servlet-api</artifactId>
<version>2.5</version>
<scope>provided</scope>
</dependency>
<dependency>
<groupId>javax.servlet.jsp</groupId>
<artifactId>jsp-api</artifactId>
<version>2.0</version>
<scope>provided</scope>
</dependency>
</dependencies>
<build>
<finalName>maven_web</finalName>
<pluginManagement><!-- lock down plugins versions to avoid using Maven defaults (may be moved to parent pom) -->
<plugins>
<!--tomcat7插件-->
<plugin>
<groupId>org.apache.tomcat.maven</groupId>
<artifactId>tomcat7-maven-plugin</artifactId>
<version>2.2</version>
<configuration>
<port>8080</port>
</configuration>
</plugin>
</plugins>
</pluginManagement>
</build>
</project>
添加完成后,使用tomcat7:run命令启动即可。

这样就可以成功访问jsp页面了。
2.无法访问servlet
在访问servlet时页面显示为404

解决方案
在web.xml中进行配置,添加上servlet的url路径
修改前:
<!DOCTYPE web-app PUBLIC
"-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
"http://java.sun.com/dtd/web-app_2_3.dtd" >
<web-app>
<display-name>Archetype Created Web Application</display-name>
<servlet>
<servlet-name>TestServlet</servlet-name>
<servlet-class>org.example.servlet.TestServlet</servlet-class>
</servlet>
</web-app>
修改后:
<!DOCTYPE web-app PUBLIC
"-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
"http://java.sun.com/dtd/web-app_2_3.dtd" >
<web-app>
<display-name>Archetype Created Web Application</display-name>
<servlet>
<servlet-name>TestServlet</servlet-name>
<servlet-class>org.example.servlet.TestServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>TestServlet</servlet-name>
<url-pattern>/testServlet</url-pattern>
</servlet-mapping>
</web-app>
再次运行即可成功。


本文指导如何修复Maven中JSP编译错误,包括检查jar包冲突、设置servlet-api和jsp-api为provided scope,以及调整Tomcat版本以匹配JRE。还介绍了处理servlet访问404问题和web.xml配置的调整。
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