如何从后端Java代码发送PDF文件？

Question

我有一个 JSP 文件，有后端帮助程序类。我需要从后端助手将 PDF 文件作为附件发送到 JSP。我怎样才能做到这一点？

Answer 1

我建议您使用 Apache Commons File Upload 组件。这可能是最好的方法，而不是重新发明轮子。 ;)

Answer 2

由于您没有告诉我们您是否使用任何 MVC 框架或只是简单的 Servlet，因此我将介绍基础知识。

如果您想上传文件，Apache Commons File Upload 是最好的库，它将翻译您的 multipart/form-data 编码的 HttpServletRequest 消息，并为您提供上传的文件（在InputStream 格式，大多是首选）。

作为开发人员，您可以将数据写回到您选择的持久存储中。

相反，它获取文件，获取适当的 MIME-Type、Content-Length（文件大小）和文件数据（InputStream，如果可能）并将其渲染回 HttpServletResponse ）。

这段代码（功能齐全，由我编写）确实将文件作为附件/内联。

import java.io.BufferedInputStream;
import java.io.ByteArrayOutputStream;
import java.io.Closeable;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;

import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletResponse;


/**
 * @author Buhake Sindi (The Elite Gentleman)
 * @since 01 September 2011
 */
public class FileServletRenderer implements ServletRenderer {

  private static final int DEFAULT_BUFFER_SIZE = 10240; // 10KB
  private static final String OCTECT_STREAM_MIME_TYPE = "application/octect-stream";
  private String contentType = OCTECT_STREAM_MIME_TYPE;
  private long contentLength;
  private String contentDisposition = "inline";
  private String fileName;
  private InputStream inputStream;

  /**
   * @return the contentType
   */
  public String getContentType() {
    return contentType;
  }

  /**
   * @param contentType
   *          the contentType to set
   */
  public void setContentType(String contentType) {
    this.contentType = contentType;
  }

  /**
   * @return the contentLength
   */
  public long getContentLength() {
    return contentLength;
  }

  /**
   * @param contentLength
   *          the contentLength to set
   */
  public void setContentLength(long contentLength) {
    this.contentLength = contentLength;
  }

  /**
   * @return the contentDisposition
   */
  public String getContentDisposition() {
    return contentDisposition;
  }

  /**
   * @param contentDisposition
   *          the contentDisposition to set
   */
  public void setContentDisposition(String contentDisposition) {
    this.contentDisposition = contentDisposition;
  }

  /**
   * @return the fileName
   */
  public String getFileName() {
    return fileName;
  }

  /**
   * @param fileName
   *          the fileName to set
   */
  public void setFileName(String fileName) {
    this.fileName = fileName;
  }

  /**
   * @return the inputStream
   */
  public InputStream getInputStream() {
    return inputStream;
  }

  /**
   * @param inputStream
   *          the inputStream to set
   */
  public void setInputStream(InputStream inputStream) {
    this.inputStream = inputStream;
  }

  public void setFile(File file) throws IOException {
    if (file == null) {
      throw new IOException("file is null.");
    }

    setInputStream(new BufferedInputStream(new FileInputStream(file)));
    setContentLength(file.length());
  }

  /*
   * (non-Javadoc)
   * 
   * @see org.bfs.bayweb.util.renderer.ServletViewRenderer#render(javax.servlet.
   * ServletRequest, javax.servlet.ServletResponse)
   */
  public void render(ServletRequest request, ServletResponse response) throws IOException {
    // TODO Auto-generated method stub
    BufferedOutputStream bos = new BufferedOutputStream(response.getOutputStream());

    try {
      byte[] buffer = new byte[DEFAULT_BUFFER_SIZE];
      int inputStreamLength = 0;
      int length = 0;

      if (contentType == null) {
        contentType = request.getServletContext().getMimeType(getFileName());
      }

      //We couldn't determine Content-Type
      if (contentType == null) {
        contentType = OCTECT_STREAM_MIME_TYPE;
      }

      while ((length = getInputStream().read(buffer)) > 0) {
        inputStreamLength += length;
        bos.write(buffer, 0, length);
      }

      if (inputStreamLength != getContentLength()) {
        setContentLength(inputStreamLength);
      }

      if (response instanceof HttpServletResponse) {
        HttpServletResponse httpResponse = (HttpServletResponse) response;
        httpResponse.reset();
        httpResponse.setHeader("Content-Type", getContentType());
        httpResponse.setHeader("Content-Length", String.valueOf(getContentLength()));
        httpResponse.setHeader("Content-Disposition", "\"" + getContentDisposition() + "\""
            + ((getFileName() != null && !getFileName().isEmpty()) ? "; filename=\"" + getFileName() + "\"" : ""));
        httpResponse.setHeader("Content-Type", getContentType());
      }

      // finally
      bos.flush();

      // clear
    } finally {
      // TODO Auto-generated catch block
      close(bos);
      close(getInputStream());
    }
  }

  private void close(Closeable resource) throws IOException {
    if (resource != null) {
      resource.close();
    }
  }
}

最重要的方法是render(HttpServletRequest, HttpServletResponse)。