如何从jsp的本地路径显示图像

Question

我正在尝试显示图像 throw jsp。图像存储在本地路径中，因此我编写了一个 servlet 获取方法来检索图像，并在图像标记的 src 属性中，我将 servlet 名称和图像路径作为参数提供给 servlet，这是我的代码，

public class FileServlet extends HttpServlet {
private static final long serialVersionUID = 1L;

private static final int DEFAULT_BUFFER_SIZE = 10240; // 10KB.
private String filePath;
 public void init() throws ServletException {

    this.filePath = "/files";
}

protected final void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    System.out.println("In do get");

    // Get requested file by path info.
    String requestedFile = request.getPathInfo();

    // Check if file is actually supplied to the request URI.
    if (requestedFile == null) {
        // Do your thing if the file is not supplied to the request URI.
        // Throw an exception, or send 404, or show default/warning page, or just ignore it.
        response.sendError(HttpServletResponse.SC_NOT_FOUND); // 404.
        return;
    }

    // Decode the file name (might contain spaces and on) and prepare file object.
    File file = new File(filePath, URLDecoder.decode(requestedFile, "UTF-8"));

    // Check if file actually exists in filesystem.
    if (!file.exists()) {
        // Do your thing if the file appears to be non-existing.
        // Throw an exception, or send 404, or show default/warning page, or just ignore it.
        response.sendError(HttpServletResponse.SC_NOT_FOUND); // 404.
        return;
    }

    // Get content type by filename.
    String contentType = getServletContext().getMimeType(file.getName());

    // If content type is unknown, then set the default value.
    // For all content types, see: http://www.w3schools.com/media/media_mimeref.asp
    // To add new content types, add new mime-mapping entry in web.xml.
    if (contentType == null) {
        contentType = "application/octet-stream";
    }

    // Init servlet response.
    response.reset();
    response.setBufferSize(DEFAULT_BUFFER_SIZE);
    response.setContentType(contentType);
    response.setHeader("Content-Length", String.valueOf(file.length()));
    response.setHeader("Content-Disposition", "attachment; filename=\"" + file.getName() + "\"");

    // Prepare streams.
    BufferedInputStream input = null;
    BufferedOutputStream output = null;

    try {
        // Open streams.
        input = new BufferedInputStream(new FileInputStream(file), DEFAULT_BUFFER_SIZE);
        output = new BufferedOutputStream(response.getOutputStream(), DEFAULT_BUFFER_SIZE);

        // Write file contents to response.
        byte[] buffer = new byte[DEFAULT_BUFFER_SIZE];
        int length;
        while ((length = input.read(buffer)) > 0) {
            output.write(buffer, 0, length);
        }
    } finally {
        // Gently close streams.
        close(output);
        close(input);
    }
}

protected final void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    System.out.println("In do post");

}


private static void close(Closeable resource) {
    if (resource != null) {
        try {
            resource.close();
        } catch (IOException e) {
            // Do your thing with the exception. Print it, log it or mail it.
            e.printStackTrace();
        }
    }
}

在web.xml中servlet入口如下，

<servlet>
<description>
</description>
<display-name>FileServlet</display-name>
<servlet-name>FileServlet</servlet-name>
<servlet-class>com.mypackage.FileServlet</servlet-class>
</servlet>

<servlet-mapping>
<servlet-name>FileServlet</servlet-name>
<url-pattern>/file/*</url-pattern>
</servlet-mapping>

在 Jsp 中我有如下 img 标签，

<img alt="Image" src="file/D:/uploads/img14.jsp" width="160" height="160"    class="img-thumbnail">

我认为我在 img 标签的 src 属性中犯了错误，谁能告诉我在这里犯了什么错误。

Answer 1

你的 img 标签的 src 属性应该像这样发送请求到你的 servlet。 src="${pageContext.request.contextPath}/FileServlet/getImage?path=D:\offline_registration\11022017\unzip\a89a89e9-5de2-4bb2-9225-e465bb5705b1.jpeg"

这里的路径变量包含来自本地系统的图像路径。

Answer 2

我尝试了下面的代码，它在 servlet 和 java 中都可以正常工作。如果使用下面的代码在servlet中将图像转换为字节，则在会话属性中设置转换后的字节码并获取jsp。

注意：可以显示任何格式的图片

package Jx_Test;
import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.UnsupportedEncodingException;

import org.apache.commons.codec.binary.Base64;

public class Imag {

    public static void main(String[] args) throws FileNotFoundException, UnsupportedEncodingException {
        // TODO Auto-generated method stub
         File file = new File("C:\\Users\\Public\\Pictures\\Sample Pictures\\Desert.jpg");

            FileInputStream fis = new FileInputStream(file);
            //create FileInputStream which obtains input bytes from a file in a file system
            //FileInputStream is meant for reading streams of raw bytes such as image data. For reading streams of characters, consider using FileReader.

            ByteArrayOutputStream bos = new ByteArrayOutputStream();
            byte[] buf = new byte[1024];
            try {
                for (int readNum; (readNum = fis.read(buf)) != -1;) {
                    //Writes to this byte array output stream
                    bos.write(buf, 0, readNum); 
                    System.out.println("read " + readNum + " bytes,");
                }
            } catch (IOException ex) {
               // Logger.getLogger(ConvertImage.class.getName()).log(Level.SEVERE, null, ex);
            }

            byte[] bytes = bos.toByteArray();

            byte[] encodeBase64 = Base64.encodeBase64(bytes);
            String base64Encoded = new String(encodeBase64, "UTF-8");


            System.out.println(base64Encoded);
    }

}

//Jsp
<img src="data:image/jpeg;base64,<%=base64Encoded%>"/>

Answer 3

您似乎误解了 BalusC 的帖子：FileServlet。在这种情况下，您的磁盘中将有一个用于服务器文件的基本路径（在服务器中的 Web 应用程序文件夹路径之外），然后您的 URL 中使用的路径将用于搜索内部这个基本路径。请注意 BalusC 的示例如何调用资源：

<a href="file/foo.exe">download foo.exe</a>

地点：

• file 是 Servlet 的 URL 模式。在您的 web.xml 配置中注明：

  <servlet-mapping>
  <servlet-name>FileServlet</servlet-name>
  <url-pattern>/file/*</url-pattern>
  </servlet-mapping>
  

• URL /foo.exe 的其余部分是文件在服务器硬盘中的位置。这可以通过使用HttpServletRequest.html#getPathInfo

轻松获得

这部分代码说明了这一点（cmets 是我的）：

public void init() throws ServletException {
    this.filePath = "/files";
}

protected void doGet(HttpServletRequest request, HttpServletResponse response)
    throws ServletException, IOException {
    // Get the file path from the URL.
    String requestedFile = request.getPathInfo();

    //...
    //using filePath attribute in servletclass as the base path
    //to lookup for the files, using the requestedFile
    //path to seek for the existance of the file (by name)
    //in your server
    //decoding the name in case of GET request encoding such as
    //%2F => /
    File file = new File(filePath, URLDecoder.decode(requestedFile, "UTF-8"));
    //...
}

然后，当有这样的请求时（在您的视图中的 HTML 代码中）：

<img src="files/img/myimage.png" />

您必须确保该文件存在于您的服务器中：

- /  <-- root
  - /files <-- this is the base file path set in init method in your servlet
    - /img
      - myimage.png

更多信息：

• BalusC's FileServlet blog entry
• What's the difference between getRequestURI and getPathInfo methods in HttpServletRequest?

Answer 4

您犯的错误是试图将您的 JSP 页面调用为图像资源。 JSP 本身只是一个文本文件。您需要将文件的路径替换为服务器上将编译/提供 JSP 页面结果（即图像）的页面的 url。如果它在本地服务器上，通常 url 看起来像 http://localhost:<port>/.../img14.jsp。