spring-boot创建最简单的web应用

初衷

看了一下spring-boot相关的书籍,创建一个hello world!的应用,是那么的简单。然而,自己动手,却很不一样。

首先,我们只是创建一个简单的hello world!并不打算使用默认的thymeleaf,而是使用传统的jsp。
当然,我们不能把自己限制于一个简单的hello world!我们要的是具有热部署功能的!

spring-boot + 内置tomcat + jsp

一、初始化项目:

我们只是构建一个hello world! 的web应用。
打包方式选择war
起步依赖只需要选择Web和DevTools即可。

二、处理jsp目录

springboot默认提供thymeleaf的模板,对于从传统web开发转过来的人来说,不喜欢!
然而 spring boot并没有给我们初始化webapp目录。所以,还是手动吧。

在“src/main”下创建“webapp/WEB_INF/jsp”目录
并且在webapp目录下新建index.jsp, 内容为hello world页面。
注意是webapp目录下,不是“webapp/WEB-INF/jsp”目录。

题外话:如果你甘愿hello world!那就hello吧,反正我是 change the world!

三、处理pom.xml(添加jsp支持、war的插件)

1、然后添加jsp需要的依赖jstl

<dependency>
<groupId>javax.servlet</groupId>
<artifactId>jstl</artifactId>
</dependency>

2、jsp编译需要的依赖

<dependency>
<groupId>org.apache.tomcat.embed</groupId>
<artifactId>tomcat-embed-jasper</artifactId>
</dependency>

3、把spring-boot-starter-tomcat的provided属性注释掉

4、再添加一个插件(由于选择的是war包方式)

<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-surefire-plugin</artifactId>
    <configuration>
        <useSystemClassLoader>false</useSystemClassLoader>
    </configuration>
</plugin>

四、配置application.properties

server.port=9090

spring.thymeleaf.cache=false
spring.thymeleaf.enabled=false
spring.mvc.view.prefix=/
spring.mvc.view.suffix=.jsp

五、启动应用

执行main方法启动应用
启动后访问localhost:9090即可

六、处理完后的pom.xml是先这样子的

<?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/4.0.0http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.lgh</groupId>
    <artifactId>sample</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>war</packaging>

    <name>sample</name>
    <description>Demo project for Spring Boot</description>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.0.2.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <java.version>1.8</java.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>jstl</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-tomcat</artifactId>
            <!--<scope>provided</scope>-->
        </dependency>
        <dependency>
            <groupId>org.apache.tomcat.embed</groupId>
            <artifactId>tomcat-embed-jasper</artifactId>
            <!--<scope>provided</scope>-->
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-devtools</artifactId>
            <scope>runtime</scope>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-surefire-plugin</artifactId>
                <configuration>
                    <useSystemClassLoader>false</useSystemClassLoader>
                </configuration>
            </plugin>
        </plugins>
    </build>
</project>

spring-boot + 外置tomcat + jsp

一、同样的方式初始化项目

二、同样的方式处理jsp目录

三、处理pom.mxl(添加jsp支持、war插件及排除掉)

1、然后添加jsp需要的依赖jstl

<dependency>
<groupId>javax.servlet</groupId>
<artifactId>jstl</artifactId>
</dependency>

2、start-web排除掉tomcat

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
    <exclusions>
        <exclusion>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-tomcat</artifactId>
        </exclusion>
    </exclusions>
</dependency>

3、添加servlet-api

<dependency>
    <groupId>javax.servlet</groupId>
    <artifactId>javax.servlet-api</artifactId>
    <version>3.1.0</version>
    <scope>provided</scope>
</dependency>

4、删除spring-boot-starter-tomcat依赖

5、同样添加一个插件

<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-surefire-plugin</artifactId>
    <configuration>
        <useSystemClassLoader>false</useSystemClassLoader>
    </configuration>
</plugin>

四、同样的配置application.properties

五、启动应用

(idea中)在run/debug configuration窗口中,添加tomcatServer,配置部署即可
注意这种方式,application.properties中的server.port是不生效的。

六、处理完后的pom.xml是先这样子的

<?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>com.lgh</groupId>
    <artifactId>client</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>war</packaging>

    <name>client</name>
    <description>Demo project for Spring Boot</description>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.0.2.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <java.version>1.8</java.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
            <exclusions>
                <exclusion>
                    <groupId>org.springframework.boot</groupId>
                    <artifactId>spring-boot-starter-tomcat</artifactId>
                </exclusion>
            </exclusions>
        </dependency>
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>jstl</artifactId>
        </dependency>
    
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>javax.servlet-api</artifactId>
            <version>3.1.0</version>
            <scope>provided</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-devtools</artifactId>
            <scope>runtime</scope>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
                <configuration>
                    <fork>true</fork>
                </configuration>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-surefire-plugin</artifactId>
                <configuration>
                    <useSystemClassLoader>false</useSystemClassLoader>
                </configuration>
            </plugin>
            <plugin>
                <artifactId>maven-compiler-plugin</artifactId>
                <configuration>
                    <source>1.8</source>
                    <target>1.8</target>
                </configuration>
            </plugin>
        </plugins>
    </build>


</project>

踩过的坑,吃过的屎

没有热部署,特别难受

1、添加一个依赖(初始化时如果选了就不需要手动添加了)

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-devtools</artifactId>
    <scope>runtime</scope>
</dependency>

2、插件添加配置(里面的configuration节点加上)

<plugin>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-maven-plugin</artifactId>
    <configuration>
        <fork>true</fork>
    </configuration>
</plugin>

添加了上面的两个配置后,修改java代码后,idea中可以右键recompile重新编译
如果是在本地tomcat的情况下,idea会提示reload class。
如果是在spring boot内置的tomcat的情况下,应用会自动重启。

不同的引导方式,不同的报错信息

首先,我们用idea创建的项目中,pom.xml文件是长这样的

<?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/4.0.0http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.lgh</groupId>
    <artifactId>sample</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>war</packaging>

    <name>sample</name>
    <description>Demo project for Spring Boot</description>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.0.2.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <java.version>1.8</java.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-devtools</artifactId>
            <scope>runtime</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-tomcat</artifactId>
            <scope>provided</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>


</project>

为了支持jsp,我们加入两个依赖

<dependency>
    <groupId>javax.servlet</groupId>
    <artifactId>jstl</artifactId>
</dependency>
<dependency>
    <groupId>org.apache.tomcat.embed</groupId>
    <artifactId>tomcat-embed-jasper</artifactId>
    <scope>provided</scope>
</dependency>

由于我们选择了war的打包方式,你会发现,自动创建了一个ServletInitializer类。
由于是war,还需要添加一个插件

<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-surefire-plugin</artifactId>
    <configuration>
        <useSystemClassLoader>false</useSystemClassLoader>
    </configuration>
</plugin>

我们再src/main下创建“webapp”目录,并创建一个index.jsp文件
(还要去配置application.properties文件,把默认的模板禁用掉)

以上步骤是大部分博客的过程。这时候,我们直接用main方法的方式启动时,是酱紫的

spring-boot创建最简单的web应用

解决办法是:
把pom文件中的spring-boot-starter-tomcat 和 tomcat-embed-jasper的 provided属性注释掉。
注释掉后,启动起来,访问localhost:8080即可看到hello world!

回到注释provided属性前,如果这时候我们把ServletInitializer注释掉
把Application类继承SpringBootServletInitializer, 像这样子

@SpringBootApplication
public class ClientApplication extends SpringBootServletInitializer{

@Override
protected SpringApplicationBuilder configure(SpringApplicationBuilder application) {
    return application.sources(ClientApplication.class);
}

public static void main(String[] args) {
    SpringApplication.run(ClientApplication.class, args);
}

}

此时执行main方法启动应用,报错如下
org.springframework.beans.factory.BeanDefinitionStoreException: Failed to parse configuration class [com.lgh.client.ClientApplication]; nested exception is java.lang.IllegalStateException: Failed to introspect annotated methods on class org.springframework.boot.web.servlet.support.SpringBootServletInitializer

spring-boot创建最简单的web应用

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