Daily Plan

更新: 5/3/2025 字数: 0 字 时长: 0 分钟

• Acwing + LeetCode
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Daily Study

更新: 5/3/2025 字数: 0 字 时长: 0 分钟

SpringBoot配置和简单应用

步骤

1. 安装Java
2. 安装Maven
3. 创建Spring Boot项目
4. 构建和运行 Spring Boot 应用

创建Spring Boot项目

创建一个新目录作为项目根目录，并进入该目录：

mkdir my-spring-boot-app && cd my-spring-boot-app

创建 Maven 项目结构：

mkdir -p src/main/java/hello

创建项目的 pom.xml 文件：在 my-spring-boot-app 目录下创建一个 pom.xml 文件，内容如下

<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.example</groupId>
    <artifactId>my-spring-boot-app</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>

    <name>my-spring-boot-app</name>
    <description>Demo project for Spring Boot</description>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.3.4.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>

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

    <properties>
        <java.version>8</java.version> # 注意这里的Java版本！！！
    </properties>

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

创建一个简单的 Spring Boot 应用程序： 在 src/main/java/hello 目录下创建一个名为 HelloApplication.java 的文件，内容如下：

package hello;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class HelloApplication {

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

在 src/main/java/hello 目录下创建一个名为 HelloController.java 的文件，内容如下：

package hello;

import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class HelloController {

    @GetMapping("/")
    public String index() {
        return "Greetings from Spring Boot!";
    }
}

构建和运行 Spring Boot 应用，返回到项目根目录（my-spring-boot-app），运行 Maven 打包命令：

mvn package

运行构建好的 JAR 文件：

java -jar target/my-spring-boot-app-0.0.1-SNAPSHOT.jar

在Docker虚拟机Linux3上碰见的BUG

BUG1

环境： java-version：OpenJDK11.0.20.1 Mvn-version：3.6.3 报错：

[ERROR] Error executing Maven. 
[ERROR] java.lang.IllegalStateException: Unable to load cache item [ERROR] Caused by: Unable to load cache item [ERROR] Caused by: Could not initialize class com.google.inject.internal.cglib.core.$MethodWrapper[ERROR] Caused by: Exception com.google.inject.internal.cglib.core.$CodeGenerationException: java.lang.reflect.InaccessibleObjectException-->Unable to make protected final java.lang.Class java.lang.ClassLoader.defineClass(java.lang.String,byte[],int,int,java.security.ProtectionDomain) throws java.lang.ClassFormatError accessible: module java.base does not "opens java.lang" to unnamed module @365c30cc [in thread "main"]

解决办法： java - Maven crashes when trying to compile a project "Error executing Maven." - Stack Overflow Looks like that version of maven doesn't work on Java 9, but it does on Java 8.

Ensure that you have the relevant packages installed, e.g...

sudo apt install openjdk-8-jre openjdk-8-jdk

And then make sure that maven uses the correct version. The simplest way to do this is to add the following line to the end of ~/.mavenrc (Creating it if needed):

export JAVA_HOME=/usr/lib/jvm/java-8-openjdk-amd64/

(You might need to look around in /usr/lib/jvm/ for the exact name you need as it might be different for your system)

BUG2

在进行了BUG1的修复后 再次运行报错

[ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.8.1:compile (default-compile) on project my-spring-boot-app: Fatal error compiling: invalid target release: 11 -> [Help 1] 
[ERROR] 
[ERROR] To see the full stack trace of the errors, re-run Maven with the -e switch. 
[ERROR] Re-run Maven using the -X switch to enable full debug logging. 
[ERROR] 
[ERROR] For more information about the errors and possible solutions, please read the following articles: 
[ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/MojoExecutionException

解决办法： 修改pom.xml文件中的java版本，找到下列内容修改

<properties>
    <java.version>1.8</java.version>
</properties>

Daily Problem

更新: 5/3/2025 字数: 0 字 时长: 0 分钟