Servlet 停止，没有给出任何异常

Question

我已经在 Mandriva Linux 上的 Tomcat 6 服务器上实现了托管的 Servlet。我已经能够让客户端与Servlet进行通信。为了响应请求，Servlet 尝试实例化位于同一目录中的另一个类（名为 KalmanFilter）。卡尔曼滤波器尝试创建四个矩阵（使用 Jama Matrix 包）。但此时 Servlet 停止了，没有给出任何异常！

但是，从同一目录中的另一个测试代码，我已经能够创建 KalmanFilter 类的实例，并继续执行，不会出现任何错误。仅当我的 Servlet 尝试实例化 KalmanFilter 类并创建矩阵时，才会出现此问题。有什么想法吗？

以下是代码：

MyServlet.java

import javax.servlet.*;
import javax.servlet.http.*;
import java.io.*;
import java.util.*;

public class MyServlet extends HttpServlet {   
public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException{
    doGet(request, response);
}
public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException{  
    PrintWriter out = null;  //response.getWriter();    
    try{                            
        System.out.println("creating new KalmanFilter");
        KalmanFilter filter = new KalmanFilter();                       
        out = response.getWriter(); 
        out.print("filter created");                
    }catch(Exception ex){  
        ex.printStackTrace();
        System.out.println("Exception in doGet(): " + ex.getMessage());
        ex.printStackTrace(out);
    } 
}  
}

KalmanFilter.java

import Jama.Matrix;

public class KalmanFilter {

protected Matrix X, X0;
protected Matrix F, Q;
//protected Matrix F, B, U, Q;
protected Matrix H, R;
protected Matrix P, P0;

private final double EPSILON = 0.001;

public KalmanFilter(){
    System.out.println("from constructor of KalmanFilter");
    createInitialMatrices();                
}

private void createInitialMatrices(){
    System.out.println("from KalmanFilter.createInitialMatrices()");

    double[][] pVals = {
            {1.0, 0.0},
            {0.0, 1.0}
        };

    double[][] qVals = {
            {EPSILON, EPSILON},
            {EPSILON, EPSILON}
        };

    double[][] hVals = {
            {1.0, 0.0},
            {0.0, 1.0},
            {1.0, 0.0},
            {0.0, 1.0}
        };

    double[][] xVals = {
            {0.0},
            {0.0},
        };

    System.out.println("creating P Q H X matrices in createInitialMatrices()");

    try{
        this.P = new Matrix(pVals);
        System.out.println("created P  matrix in createInitialMatrices()");
        this.Q = new Matrix(qVals);
        System.out.println("created Q  matrix in createInitialMatrices()");
        this.H = new Matrix(hVals);
        System.out.println("created H  matrix in createInitialMatrices()");
        this.X = new Matrix(xVals);
        System.out.println("created X  matrix in createInitialMatrices()");
        System.out.println("created P Q H X matrices in  createInitialMatrices()");
    }catch(Exception e){
        System.out.println("Exception from createInitialMatrices()"+ e.getMessage());
        e.printStackTrace();
    }
    System.out.println("returning from createInitialMatrices()");       
}               
}

Answer 1

如果您从 servlet 中删除了 try/catch 块，那么诊断起来会更容易。此代码抛出的唯一已检查异常是 IOException，而 doGet 允许您抛出该异常，而无需自己捕获它。

public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException{  
    System.out.println("creating new KalmanFilter");
    KalmanFilter filter = new KalmanFilter();                       
    out = response.getWriter(); 
    out.print("filter created");                
}  

这样，异常将显示在浏览器上，而不是消失在日志文件中。当然，这对于用户来说并不是很好，但是对于您的开发来说，它让生活变得更轻松。