Question

每次运行程序时都会出现NullPointerException，我不知道该怎么做才能让它工作。它应该解析输入文件数据，进行一些计算（所有都没有编码），然后打印到输出文件。

以下是我的课程：

驱动：

public class Driver
{
    public static void main(String[] args) throws IOException
    {
        Analyzer start = new Analyzer();
        start.start();  
    }
}

分析仪：

public class Analyzer 
{
    public void start() throws IOException
    {       
        int total = 0;
        int totalError = 0;
        final int SIZE = 31;
        Response data[] = new Response[SIZE];

        PrintWriter out = new PrintWriter(new FileWriter("apacheOut.txt"));

        Scanner scan = new Scanner (new File("access_log1.txt"));
        while(scan.hasNext())
        {   
            String address = scan.next();
            scan.next(); //garbage line
            scan.next(); //garbage line

            String date = scan.next() + " " + scan.next(); 

            String temp = scan.next();
            String request = temp.substring(1);
            scan.next(); //garbage line

            int status = 0;
            while(status == 0)
            {
                if(scan.hasNextInt())
                    status = scan.nextInt();
                else
                    scan.next(); //garbage line
            }

            int bytes = 0;
            if(status < 300)
            {
                if(scan.hasNextInt())
                {
                    bytes = scan.nextInt();
                }
                else
                {
                    scan.next(); //garbage line
                } 
            }

            String referAgent = scan.nextLine();

            if(status < 400)
            {
                SuccessResponse srp = new SuccessResponse(address, date, request, status, bytes, referAgent);
            }
            else
            {
                ErrorResponse err = new ErrorResponse(address, date, request, status, bytes, referAgent);
                totalError++;
            }

            total++;    
        }

        int numGet = 0;
        int numPost = 0;
        double numBytes = 0;
        for (int i = 0; i <= SIZE; i++)
        {   
            String address = data[i].getAddress();
            String date = data[i].getDate();
            String request = data[i].getRequest();
            int status = data[i].getStatus();
            int bytes = data[i].getBytes();
            String referAgent = data[i].getReferAgent();

            /** GET/POST count */
            if (request.substring(0,1) == "G")
            {   
                numGet++;
            }
            else if (request.substring(0,1) == "P")
            {
                numPost++;
            }

            /** Number of total bytes */
            numBytes = bytes++;
        }

        out.println ("Warren Smith's Results");
        out.println ("======================");
        out.println ("The total number of requests in the file: " + total);
        out.println ("The total number of GET requests: " + numGet);
        out.println ("The total number of POST requests: " + numPost);
        out.println ("The total number of bytes served: " + numBytes);
        out.println ("The number & percentage of pages producing various status categorizations:" );
        out.println ("    1xx Informational: ");
        out.println ("    2xx Status: ");
        out.println ("    3xx Redirection: ");
        out.println ("    4xx Client Error: ");
        out.println ("    5xx Server Error: ");
        out.println ("The percentage and number of Windows-based clients: ");
        out.println ("The percentage and number of bad requests: " + totalError);
        out.println ("The percentage and number of clients that are Mozilla-based: ");
        out.println ("The percentage and number of requests from the Googlebot: ");

        out.close();
    }
}

响应：

abstract public class Response 
{
    protected String address;
    protected String date;
    protected String request;
    protected int status;
    protected int bytes;
    protected String referAgent;

    /** Response object constructor */
    public Response (String eAddress, String eDate, String eRequest, int eStatus, int eBytes, String eReferAgent)
    {
        address = eAddress;
        date = eDate;
        request = eRequest;
        status = eStatus;
        bytes = eBytes;
        referAgent = eReferAgent;
    }

    /** Returns the IP address */
    public String getAddress()
    {
        return address;
    }

    /** Returns the date */
    public String getDate()
    {
        return date;
    }

    /** Returns the request to server */
    public String getRequest()
    {
        return request;
    }

    /** Returns the status code */
    public int getStatus()
    {
        return status;
    }   

    /** Returns the # of bytes */
    public int getBytes()
    {
        return bytes;
    }

    /** Returns the referring page & agent */
    public String getReferAgent()
    {
        return referAgent;
    }
}

SuccessResponse：

public class SuccessResponse extends Response
{
    /** SuccessResponse object constructor */
    public SuccessResponse (String eAddress, String eDate, String eRequest, int eStatus, int eBytes, String eReferAgent)
    {
        super (eAddress, eDate, eRequest, eStatus, eBytes, eReferAgent);
    }

    /** Returns the IP address */
    public String getAddress()
    {
        return address;
    }

    /** Returns the date */
    public String getDate()
    {
        return date;
    }

    /** Returns the request to server */
    public String getRequest()
    {
        return request;
    }

    /** Returns the status code */
    public int getStatus()
    {
        return status;
    }   

    /** Returns the # of bytes */
    public int getBytes()
    {
        return bytes;
    }

    /** Returns the referring page */
    public String getReferAgent()
    {
        return referAgent;
    }
}

错误响应：

public class ErrorResponse extends Response
{
    /** ErrorResponse object constructor */
    public ErrorResponse (String eAddress, String eDate, String eRequest, int eStatus, int eBytes, String eReferAgent)
    {
        super (eAddress, eDate, eRequest, eStatus, eBytes, eReferAgent);
    }

    /** Returns the request to server */
    public String getRequest()
    {
        return request;
    }

    /** Returns the status code */
    public int getStatus()
    {
        return status;
    }   

    /** Returns the # of bytes */
    public int getBytes()
    {
        return bytes;
    }

    /** Returns the referring page */
    public String getReferAgent()
    {
        return referAgent;
    }
}

这个输出是：

[java] Exception in thread "main" java.lang.NullPointerException
[java]     at Analyzer.start(Unknown Source)
[java]     at Driver.main(Unknown Source)
[java] Java Result: 1

为什么NullPointerException会不断出现？

Answer 1

似乎data数组中的元素未初始化，但您尝试使用它们调用方法。

在运行时出于未知原因的NullPointerException

1 个答案: