SpringMVC4-组件(五)-MultipartResolver

《看透springMvc源代码分析与实践》学习笔记
SpringMVC 版本 4.1.5.RELEASE

MultipartResolver

MultipartResolver用于处理文件上传，它的接口定义如下：

public interface MultipartResolver {
    //判断request是否为文件上传请求
    boolean isMultipart(HttpServletRequest request);
    
    //将 HttpServletRequest 转换为 MultipartHttpServletRequest
    MultipartHttpServletRequest resolveMultipart(HttpServletRequest request) throws MultipartException;
    
    //清空： 入参是MultipartHttpServletRequest
    void cleanupMultipart(MultipartHttpServletRequest request);
}

MultipartResolver有两个实现类：

• StandardServletMultipartResolver: 使用Servlet3.0标准的上传方式,将HttpServletRequest转换为StandardMultipartHttpServletRequest。
• CommonsMultipartResolver: 使用Apache的common-fileupload,将HttpServletRequest转换为DefaultMultipartHttpServletRequest。

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MultipartHttpServletRequest

文件上传处理过程中使用的是MultipartHttpServletRequest,它继承自接口MultipartRequest.

SpringMVC提供了两种实现：StandardMultipartHttpServletRequest和DefaultMultipartHttpServletRequest，
他们有着同一个父类AbstractMultipartHttpServletRequest,MultipartHttpServletRequest接口定义的方法基本都在AbstractMultipartHttpServletRequest中实现。

AbstractMultipartHttpServletRequest

//org.springframework.web.multipart.support.AbstractMultipartHttpServletRequest
public abstract class AbstractMultipartHttpServletRequest extends HttpServletRequestWrapper implements MultipartHttpServletRequest {
	//注意： MultiValueMap 等价于 Map<String ,List<MultipartFile>>
	private MultiValueMap<String, MultipartFile> multipartFiles;
    
    //对象自身持有了 HttpServletRequest ;
	protected AbstractMultipartHttpServletRequest(HttpServletRequest request) {
		super(request);
	}
    
    //上传时：file文件对应form表单的key(不是file自身的属性name)
	@Override
	public Iterator<String> getFileNames() {
		return getMultipartFiles().keySet().iterator();
	}
    
	@Override
	public MultipartFile getFile(String name) {
	    //由于可能上传多个文件， 这里范湖first
		return getMultipartFiles().getFirst(name);
	}
    
    //根据form表单key, 获取文件列表
	@Override
	public List<MultipartFile> getFiles(String name) {
		List<MultipartFile> multipartFiles = getMultipartFiles().get(name);
		if (multipartFiles != null) {
			return multipartFiles;
		}else {
            return Collections.emptyList();
        }
	}

	@Override
	public Map<String, MultipartFile> getFileMap() {
		return getMultipartFiles().toSingleValueMap();
	}

	@Override
	public MultiValueMap<String, MultipartFile> getMultiFileMap() {
		return getMultipartFiles();
	}
    
    //初始化时，set该属性
	protected final void setMultipartFiles(MultiValueMap<String, MultipartFile> multipartFiles) {
		this.multipartFiles = new LinkedMultiValueMap<String, MultipartFile>(Collections.unmodifiableMap(multipartFiles));
	}

}

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StandardServletMultipartResolver

StandardServletMultipartResolver使用了Servlet3.0标准的上传方式,
通过request的contentType是否以"multipart/"开头判断是否为文件上传请求,它将HttpServletRequest转换为StandardMultipartHttpServletRequest。

//org.springframework.web.multipart.support.StandardServletMultipartResolver
public class StandardServletMultipartResolver implements MultipartResolver {
	private boolean resolveLazily = false;
    
    //判断是 isMultipart
	@Override
	public boolean isMultipart(HttpServletRequest request) {
		if (!"post".equals(request.getMethod().toLowerCase())) {
			return false;
		}
		String contentType = request.getContentType();
		return (contentType != null && contentType.toLowerCase().startsWith("multipart/"));
	}
    
    //将HttpServletRequest 转换为 StandardMultipartHttpServletRequest
	@Override
	public MultipartHttpServletRequest resolveMultipart(HttpServletRequest request) throws MultipartException {
		return new StandardMultipartHttpServletRequest(request, this.resolveLazily);
	}

	@Override
	public void cleanupMultipart(MultipartHttpServletRequest request) {
		for (Part part : request.getParts()) {
            if (request.getFile(part.getName()) != null) {
                part.delete();
            }
        }
	}
}

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CommonsMultipartResolver

CommonsMultipartResolver 使用了commons-fileupload来完成具体的上传操作。
它使用ServletFileUpload来判断是否为文件上传请求：

//使用ServletFileUpload来判断是否为文件上传请求
@Override
public boolean isMultipart(HttpServletRequest request) {
    return (request != null && ServletFileUpload.isMultipartContent(request));
}

,resolveMultipart：将HttpServletRequest 转换为 DefaultMultipartHttpServletRequest

---

使用MultipartResolver

配置

• web.xml: DispatchServlet添加<multipart-config/>配置。
• application-mvc.xml:

<!-- 注意：bean id 必须为 multipartResolver -->
<bean id="multipartResolver" class="org.springframework.web.multipart.support.StandardServletMultipartResolver">
</bean>

运行结果