java nullpointerexpection

Question

package tester;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileWriter;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.MalformedURLException;
import java.net.URL;

public class Tes {
public static void main(String[]ra)throws IOException
{
try {
URL url1=new URL("http://www.qidian.com");
InputStream in=url1.openStream();
InputStreamReader inr=new InputStreamReader(in,"utf-8");
BufferedReader br=new BufferedReader(inr);
String data=br.readLine();
FileWriter fr=new FileWriter("C:\Users\lenovo\Desktop\起点.txt");
BufferedWriter ws=new BufferedWriter(fr);
ws.write(data);
while(data!=null)
{
System.out.println(data);
data=br.readLine();
ws.write(data);
}
ws.flush();
ws.close();
fr.close();
} catch (MalformedURLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}

}
}

Exception in thread "main" java.lang.NullPointerException
at java.io.Writer.write(Unknown Source)
at tester.Tes.main(Tes.java:28)

Answer 1

while(data!=null)
{
System.out.println(data);
data=br.readLine();
if(data != null){
ws.write(data);
}
}
加一个if判断