[英]response.getOutputStream() throws IllegalStateException when called for the first time
[英]response.getOutputStream used on MySQL request throwing IllegalStateException in JSP
我面临着一个奇怪的问题。 我正在尝试创建一个网站,该网站通过从MySQL服务器检索和显示数据来动态创建“论坛线程”式的页面。 此数据可以有两种类型:纯文本或图像文件(存储为BLOB)。 在测试时,数据库中有3个条目-1个文本,1个图片,1个文本。 我们正在使用JSP和servlet检索和显示数据。 文本条目写得很好,但是当尝试显示图片时,我们不断从OutputStream实例获取IllegalStateExceptions-即,它将一直运行代码,直到我们尝试实例化OutputStream,然后抛出异常。
我们认为它与多线程有关,但是在尝试使用同步和特定的重入锁之后,我们仍然会得到异常。 我应该提到,如果我们尝试将代码的“ get-image”部分作为单独的servlet而不是JSP的一部分来运行,则它会很好地显示图像。
Servlet代码如下所示:
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);
}
}
控制台输出为:
Try-block started.
Statement created.
Statement executed.
Darn OutputStreams...
因为我们有3个ConversationID为587的条目。Content1是文本,Content2是BLOBS。
任何想法或纠正将不胜感激。 谢谢:D
您不能在同一响应中调用response.getWriter()和response.getOutputStream()。 通话
PrintWriter out = res.getWriter();
已经“声明”了响应,可以这样说,当您致电时
ServletOutputStream outStream = res.getOutputStream();
你会得到例外。
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