java - 如何从oracle sql中检索图像并将其显示在jsp页面中？

Question

Servlet 代码:

import java.io.*;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

public class profile_photo extends HttpServlet {

    /**
     * The doGet method of the servlet. <br>
     *
     * This method is called when a form has its tag value method equals to get.
     * 
     * @param request the request send by the client to the server
     * @param response the response send by the server to the client
     * @throws ServletException if an error occurred
     * @throws IOException if an error occurred
     */
    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        response.setContentType("text/html");
        PrintWriter out = response.getWriter();
        HttpSession ses=request.getSession();
        String email = (String)ses.getAttribute("ses_email");
        String imgLen="";
        Connection cn;
        PreparedStatement ps;   
        try
        {
            Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
            cn=DriverManager.getConnection("jdbc:odbc:sm","system","gecbsp");
            ps=cn.prepareStatement("select photo_loc from smreg3 where email = "+
                                "'"+email+"'");
            ResultSet rs = ps.executeQuery();
            if(rs.next()){
                  imgLen = rs.getString(1);
                  System.out.println(imgLen.length());
                  }  
            ps=cn.prepareStatement("select photo_loc from smreg3 where email = "+
                    "'"+email+"'");
            ResultSet rs2 = ps.executeQuery();
            if(rs2.next()){
                  int len = imgLen.length();
                  byte [] rb = new byte[len];
                  InputStream readImg = rs2.getBinaryStream(1);
                  int index=readImg.read(rb, 0, len);  
                  System.out.println("index"+index);
                  ps.close();
                  response.reset();
                  response.setContentType("image/jpg");
                  response.getOutputStream().write(rb,0,len);
                  response.getOutputStream().flush();  
                  }
                  }
                  catch (Exception e){
                  e.printStackTrace();
                  }
                  }

    }

Jsp代码:

<img src="${pageContext.request.contextPath}/profile_photo" />

错误:

java.lang.IllegalStateException: getWriter() has already been called for this response
at org.apache.catalina.connector.Response.getOutputStream(Response.java:573)
at org.apache.catalina.connector.ResponseFacade.getOutputStream(ResponseFacade.java:183)
at profile_photo.doGet(profile_photo.java:59)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:690)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:175)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:128)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:263)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:844)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:584)
at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:447)
at java.lang.Thread.run(Thread.java:619)

问题:

如何从 ImageServlet 中检索 JSP 中的图像？ 上述方法是从数据库检索图像的正确方法吗？或者有更好的办法吗？

Answer 1

当您声明 out 但似乎没有使用它时，您可能应该删除该行

PrintWriter out = response.getWriter();

一旦调用了 getWriter()，就无法在响应上调用 getOutputStream()。