java HttpServletRequest拷贝解决HttpServletRequest 中流只能读取一次的问题

一、遇到的问题：

接口上传了一个文件，从HttpServletRequest 中获取了文件名、文件内容等信息，后面再从HttpServletRequest 中读取文件名信息、文件内容就读取不到了

二、原因：

因为流是单向的，就像水一样被舀了一瓢就会少一瓢。所以 HttpServletRequest 对象中的 InputStream 或者 Reader 只能使用一次。

三、解决办法：

那该怎么办，复制一份HttpServletRequest 对象，把流转为字节数组存储，使用时再从字节数组中获取，可以解决。

1.用到以下依赖将输入流转化为字节数组：

<dependency>
    <groupId>commons-io</groupId>
    <artifactId>commons-io</artifactId>
    <version>2.11.0</version>
</dependency>

2.MyHttpServletRequest类继承HttpServletRequestWrapper：

import org.apache.commons.io.IOUtils;
import javax.servlet.ReadListener;
import javax.servlet.ServletInputStream;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletRequestWrapper;
import java.io.ByteArrayInputStream;
import java.io.IOException;

public class MyHttpServletRequest extends HttpServletRequestWrapper {

    private byte[] body;

    public MyHttpServletRequestWrapper(HttpServletRequest request) {
        super(request);
        try {
            body = IOUtils.toByteArray(request.getInputStream());
        } catch (IOException ex) {
            body = new byte[0];
        }
    }

    @Override
    public ServletInputStream getInputStream() throws IOException {
        return new ServletInputStream() {
            @Override
            public boolean isFinished() {
                return false;
            }

            @Override
            public boolean isReady() {
                return false;
            }

            @Override
            public void setReadListener(ReadListener readListener) {

            }

            ByteArrayInputStream bais = new ByteArrayInputStream(body);

            @Override
            public int read() throws IOException {
                return bais.read();
            }
        };
    }

}

四、测试：

测试里用到以下依赖来获取文件信息：

<dependency>
    <groupId>commons-fileupload</groupId>
    <artifactId>commons-fileupload</artifactId>
    <version>1.3.2</version>
</dependency>

public void addNewAttachment(HttpServletRequest request, HttpServletResponse response) throws Exception {
        //将request转化为newRequest，便可以使用newRequest多次读取流了
        HttpServletRequest newRequest = new MyHttpServletRequestWrapper(request);
    
    	//第一次读取
      	FileItemFactory firlfact1 = new DiskFileItemFactory();
        ServletFileUpload sfu1 = new ServletFileUpload(firlfact1);
        List<FileItem> list1 = sfu1.parseRequest(newRequest);
        for (FileItem fileItem : list1) {
               DiskFileItem diskFileItem = (DiskFileItem) fileItem;
               String fileName = diskFileItem.getName();
               System.out.println(fileName);
        }
    
    	//第二次读取
      	FileItemFactory firlfact2 = new DiskFileItemFactory();
        ServletFileUpload sfu2 = new ServletFileUpload(firlfact2);
        List<FileItem> list2 = sfu1.parseRequest(newRequest);
        for (FileItem fileItem : list2) {
               DiskFileItem diskFileItem = (DiskFileItem) fileItem;
               String fileName = diskFileItem.getName();
               tem.out.println(fileName);
        }
    
}