破解Linux内存陷阱！Spring Boot文件上传的"隐形杀手"：/tmp空间不足，99%开发者栽在它身上！

java.io.IOException: The temporary upload location [/tmp/tomcat.8080.123456789] is not valid

df -h /tmp
# 输出示例：
# tmpfs     1.8G   0  1.8G   0% /tmp

# 创建安全目录（必须！）
sudo mkdir -p /var/tmp/springboot-uploads
sudo chmod 777 /var/tmp/springboot-uploads  # 确保应用有写权限

# application.properties
# 1. JVM全局临时目录（影响所有Java操作）
-Djava.io.tmpdir=/var/tmp/springboot-uploads

# 2. Spring文件上传专用目录
spring.servlet.multipart.location=/var/tmp/springboot-uploads/upload

# 3. Tomcat工作目录（嵌入式Tomcat）
server.tomcat.basedir=/var/tmp/springboot-uploads/tomcat

# 4. 防止大文件占用内存（关键！）
spring.servlet.multipart.max-file-size=100MB
spring.servlet.multipart.max-request-size=200MB

// 日志报错：java.io.IOException: The temporary upload location is not valid
// 解决：必须提前创建目录！
File dir = new File("/var/tmp/springboot-uploads");
if (!dir.exists()) dir.mkdirs(); // 代码中自动创建（推荐）

# 错误配置：只改了multipart.location
spring.servlet.multipart.location=/var/tmp/springboot-uploads/upload

# 但JVM仍用默认/tmp → 仍会报错

# application.properties
spring.servlet.multipart.location=/var/tmp/springboot-uploads/upload
server.tomcat.basedir=/var/tmp/springboot-uploads/tomcat

# 错误：应用无权写入目录
chown -R nobody:nobody /var/tmp/springboot-uploads

@SpringBootApplication
public class App {
    public static void main(String[] args) {
        System.out.println("JVM临时目录: " + System.getProperty("java.io.tmpdir"));
        SpringApplication.run(App.class, args);
    }
}

# 上传100MB文件后
ls -lh /var/tmp/springboot-uploads/upload
# 应显示：100M的临时文件

# application.properties
# 1. JVM全局临时目录（必须！）
-Djava.io.tmpdir=/var/tmp/springboot-uploads

# 2. 文件上传专用目录
spring.servlet.multipart.location=/var/tmp/springboot-uploads/upload

# 3. Tomcat工作目录
server.tomcat.basedir=/var/tmp/springboot-uploads/tomcat

# 4. 限制文件大小（防内存溢出）
spring.servlet.multipart.max-file-size=100MB
spring.servlet.multipart.max-request-size=200MB

# 服务器初始化脚本（一键生效）
sudo mkdir -p /var/tmp/springboot-uploads/{upload,tomcat}
sudo chmod 777 /var/tmp/springboot-uploads