spring boot 2.x文件路径映射问题汇总

当我们在运行可执行的java jar包的时候，我们肯定改变不了jar里面的内容，因此文件上传路径就成了我们必须考虑的一点问题，我们不能往直接这个jar包里面写文件，那么只能写在jar包外面，但是写到jar包外面的时候要怎么通过内置的tomcat下载文件呢？springboot给我们提供了一种方式，可以将jar包外部路径映射到jar里面。接下来我们看看如何实现。
1、springboot2.0以前：我们通过继承WebMvcConfigurerAdapter来实现文件路径的映射。

@Configuration
public class FileConfig extends WebMvcConfigurerAdapter {

private String uploadPath = E://file/;

@Override
public void addResourceHandlers(ResourceHandlerRegistry registry) {
registry.addResourceHandler("/file/**").addResourceLocations("file:"+uploadPath);
super.addResourceHandlers(registry);
}
}

2、WebMvcConfigurerAdapter的内部实现
WebMvcConfigurerAdapter实现了WebMvcConfigurer接口的所有空方法。

@Deprecated
public abstract class WebMvcConfigurerAdapter implements WebMvcConfigurer {
public WebMvcConfigurerAdapter() {}

public void configurePathMatch(PathMatchConfigurer configurer) {}

public void configureContentNegotiation(ContentNegotiationConfigurer configurer) {}

public void configureAsyncSupport(AsyncSupportConfigurer configurer) {}

public void configureDefaultServletHandling(DefaultServletHandlerConfigurer configurer) {}

public void addFormatters(FormatterRegistry registry) {}

public void addInterceptors(InterceptorRegistry registry) {}

public void addResourceHandlers(ResourceHandlerRegistry registry) {}

public void addCorsMappings(CorsRegistry registry) {}

public void addViewControllers(ViewControllerRegistry registry) {}

public void configureViewResolvers(ViewResolverRegistry registry) {}

public void addArgumentResolvers(List<HandlerMethodArgumentResolver> argumentResolvers) {}

public void addReturnValueHandlers(List<HandlerMethodReturnValueHandler> returnValueHandlers) {}

public void configureMessageConverters(List<HttpMessageConverter<?>> converters) {}

public void extendMessageConverters(List<HttpMessageConverter<?>> converters) {}

public void configureHandlerExceptionResolvers(List<HandlerExceptionResolver> exceptionResolvers) {}

public void extendHandlerExceptionResolvers(List<HandlerExceptionResolver> exceptionResolvers) {}
@Nullable
public Validator getValidator() {
return null;
}

@Nullable
public MessageCodesResolver getMessageCodesResolver() {
return null;
}
}

3、WebMvcConfigurerAdapter为什么会过时？
这是因为由于Java的版本更新，在Java 8中，可以使用default关键词为接口添加默认的方法，Spring在升级的过程中也同步支持了Java 8中这一新特性。
4、新选择WebMvcConfigurer
我们看一下它实现的接口WebMvcConfigurer，既然WebMvcConfigurer默认有了空实现，我们直接实现WebMvcConfigurer接口即可。

public interface WebMvcConfigurer {
default void configurePathMatch(PathMatchConfigurer configurer) {}

default void configureContentNegotiation(ContentNegotiationConfigurer configurer) {}

default void configureAsyncSupport(AsyncSupportConfigurer configurer) {}

default void configureDefaultServletHandling(DefaultServletHandlerConfigurer configurer) {}

default void addFormatters(FormatterRegistry registry) {}

default void addInterceptors(InterceptorRegistry registry) {}

default void addResourceHandlers(ResourceHandlerRegistry registry) {}

default void addCorsMappings(CorsRegistry registry) {}

default void addViewControllers(ViewControllerRegistry registry) {}

default void configureViewResolvers(ViewResolverRegistry registry) {}

default void addArgumentResolvers(List<HandlerMethodArgumentResolver> resolvers) {}

default void addReturnValueHandlers(List<HandlerMethodReturnValueHandler> handlers) {}

default void configureMessageConverters(List<HttpMessageConverter<?>> converters) {}

default void extendMessageConverters(List<HttpMessageConverter<?>> converters) {}

default void configureHandlerExceptionResolvers(List<HandlerExceptionResolver> resolvers) {}

default void extendHandlerExceptionResolvers(List<HandlerExceptionResolver> resolvers) {}

@Nullable
default Validator getValidator() {
return null;
}

@Nullable
default MessageCodesResolver getMessageCodesResolver() {
return null;
}
}

5、更新后的代码如下：

@Configuration
public class FileConfig implements WebMvcConfigurer {

private String uploadPath = E://file/;

@Override
public void addResourceHandlers(ResourceHandlerRegistry registry) {
registry.addResourceHandler("/file/**").addResourceLocations("file:"+uploadPath);
super.addResourceHandlers(registry);
}
}

如果各位想直接使用，且用的spring boot版本在2以上，则复制第五点到项目中就好了。最后祝广大程序猿1024快乐。多长头发，少些bug。