[英]response.getOutputStream() throws IllegalStateException when called for the first time
[英]response.getOutputStream used on MySQL request throwing IllegalStateException in JSP
我面臨着一個奇怪的問題。 我正在嘗試創建一個網站,該網站通過從MySQL服務器檢索和顯示數據來動態創建“論壇線程”式的頁面。 此數據可以有兩種類型:純文本或圖像文件(存儲為BLOB)。 在測試時,數據庫中有3個條目-1個文本,1個圖片,1個文本。 我們正在使用JSP和servlet檢索和顯示數據。 文本條目寫得很好,但是當嘗試顯示圖片時,我們不斷從OutputStream實例獲取IllegalStateExceptions-即,它將一直運行代碼,直到我們嘗試實例化OutputStream,然后拋出異常。
我們認為它與多線程有關,但是在嘗試使用同步和特定的重入鎖之后,我們仍然會得到異常。 我應該提到,如果我們嘗試將代碼的“ get-image”部分作為單獨的servlet而不是JSP的一部分來運行,則它會很好地顯示圖像。
Servlet代碼如下所示:
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.sql.Blob;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
* Servlet implementation class listConversation
*/
@WebServlet("/ListConversation")
public class ListConversation extends HttpServlet
{
@Override
protected synchronized void doGet(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException
{
try
{
String connectionURL = [our database URL, username and password];
String myDriver = "com.mysql.jdbc.Driver";
Class.forName(myDriver).newInstance();
Connection con = DriverManager.getConnection(connectionURL);
Statement stmt = con.createStatement();
ResultSet rs = stmt.executeQuery("SELECT ID, Content1 FROM Conversations WHERE ConversationID=587 ORDER BY Date ASC");
res.setContentType("text/html");
PrintWriter out = res.getWriter();
out.print("<hr>");
while (rs.next())
{
out.print("<b>Besked</b><br/>" + rs.getString("Content1") + "<br/><br/>");
try {
System.out.println("Try-block started.");
Statement stmt2 = con.createStatement();
System.out.println("Statement created.");
ResultSet rs2 = stmt2.executeQuery("SELECT Content2 FROM Conversations WHERE ID = 4");
System.out.println("Statement executed.");
ServletOutputStream outStream = res.getOutputStream();
System.out.println("Outputstream initialized.");
Blob image;
if (rs2.next()) {
image = rs2.getBlob(1);
System.out.println("Image created.");
} else {
res.setContentType("text/html");
out.println("h4><font color='red'>image not found for given id</font></h4>");
return;
}
res.setContentType("image/gif");
InputStream in = image.getBinaryStream();
int length = (int) image.length();
int bufferSize = 1024;
byte[] buffer = new byte[bufferSize];
System.out.println("Initializing...");
while ((length = in.read(buffer)) != -1) {
outStream.write(buffer, 0, length);
}
System.out.println("Image streamed.");
in.close();
stmt2.close();
rs2.close();
outStream.close();
System.out.println("Closing.");
out.flush();
}
catch(IllegalStateException e)
{
System.out.println("Darn OutputStreams...");
}
catch (Exception e) {
res.setContentType("text/html");
out.println("<h4><font color='red'>Image Display Error=" + e.getMessage() +
"</font></h4>");
return;
}
out.print("<hr>");
}
stmt.close();
con.close();
}
catch (SQLException e)
{
e.printStackTrace();
}
catch (Exception e)
{
e.printStackTrace();
}
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException
{
doGet(req,res);
}
}
控制台輸出為:
Try-block started.
Statement created.
Statement executed.
Darn OutputStreams...
因為我們有3個ConversationID為587的條目。Content1是文本,Content2是BLOBS。
任何想法或糾正將不勝感激。 謝謝:D
您不能在同一響應中調用response.getWriter()和response.getOutputStream()。 通話
PrintWriter out = res.getWriter();
已經“聲明”了響應,可以這樣說,當您致電時
ServletOutputStream outStream = res.getOutputStream();
你會得到例外。
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