对于servlet转发后乱码的一个可能原因

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对于servlet转发后乱码的一个可能原因

在servlet中用request.getRequestDispatcher("../singleList.jsp").forward(request, response);转向到JSP页面后竟然发生了乱码问题，乱码问题是很常见的，不过这样出现也有点奇怪，后来处理了一下，怎么弄都是有问题。最后才发现，原来因为在servlet里面多写下了这么一句话PrintWirter out = esponse.getWriter();这句话是ECLIPSE自动生成的，因为没有用，我忘给删掉了。结果，正是他对我的程序编码产生了影响。


以下测试程序：
import java.io.IOException;  import java.io.PrintWriter;  import javax.servlet.RequestDispatcher;  import javax.servlet.ServletException;  import javax.servlet.http.HttpServlet;  import javax.servlet.http.HttpServletRequest;  import javax.servlet.http.HttpServletResponse;  public class TestServlet extends HttpServlet {    @Override    public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException {      // PrintWriter out = response.getWriter(); // 关键在这一句，如果有，则会出现乱码的。      RequestDispatcher requestDispatcher = request.getRequestDispatcher("/test/test2.jsp");      requestDispatcher.forward(request, response);    }  }

曾经尝试增加如下语句，问题依然存在


package test;  import java.io.IOException;  import java.io.PrintWriter;  import javax.servlet.RequestDispatcher;  import javax.servlet.ServletException;  import javax.servlet.http.HttpServlet;  import javax.servlet.http.HttpServletRequest;  import javax.servlet.http.HttpServletResponse;  public class TestServlet extends HttpServlet ...{    @Override    public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException ...{      PrintWriter out = response.getWriter();      response.setCharacterEncoding("UTF-8");      response.setContentType("text/html;charset=UTF-8");      RequestDispatcher requestDispatcher = request.getRequestDispatcher("/test/test2.jsp");      requestDispatcher.forward(request, response);    }  } 
去掉后，就可以正常显示汉字了，
经多次测试，发现是语句的顺序有问题，需要调整为如下的代码即可
package test;  import java.io.IOException;  import java.io.PrintWriter;  import javax.servlet.RequestDispatcher;  import javax.servlet.ServletException;  import javax.servlet.http.HttpServlet;  import javax.servlet.http.HttpServletRequest;  import javax.servlet.http.HttpServletResponse;  public class TestServlet extends HttpServlet ...{    @Override    public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException ...{      response.setCharacterEncoding("UTF-8"); // 先指定输出流的编码      PrintWriter out = response.getWriter(); // 再拿到输出对象      response.setContentType("text/html;charset=UTF-8");      RequestDispatcher requestDispatcher = request.getRequestDispatcher("/test/test2.jsp");      requestDispatcher.forward(request, response);    }  } 


总结：response.getWriter() 在内部的实现上，影响了输出结果的编码集。必须先指定编码集，在调用Writer才可以。