[英]Keep getting null pointer exception
這是我的程序:基本上我有一個xml文件,並且必須從該文件中解碼base64字符串,但是我一直在獲取NullPointerException ..請幫助! 代碼如下...
import java.io.FileInputStream;
import java.util.ArrayList;
import java.util.List;
import javax.xml.parsers.SAXParser;
import javax.xml.parsers.SAXParserFactory;
import org.xml.sax.Attributes;
import org.xml.sax.SAXException;
import org.xml.sax.helpers.DefaultHandler;
import org.apache.commons.codec.binary.Base64;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.InputStream;
import java.util.Arrays;
public class main {
public static void main(String[] args) throws Exception {
SAXParserFactory parserFactor = SAXParserFactory.newInstance();
SAXParser parser = parserFactor.newSAXParser();
SAXHandler handler = new SAXHandler();
//parser.parse(ClassLoader.getSystemResourceAsStream("ATMSPopulateDMSData.xml"),
// handler);
parser.parse(new FileInputStream("C:\\Users\\qta6754\\workspace\\Java_Dev\\XML64_Decoded\\ATMSMessageData.xml"), handler);
for (NeededInfo emp : handler.empList) {
System.out.println(emp);
}
}
}
class SAXHandler extends DefaultHandler {
List<NeededInfo> empList = new ArrayList<>();
NeededInfo emp = null;
String content = null;
String did = null;
public void startElement(String uri, String localName, String qName, Attributes attributes) throws SAXException {
switch (qName) {
case "dMSDeviceStatus":
emp = new NeededInfo();
emp.id = attributes.getValue("id");
emp.Read();
break;
}
}
public void characters(char[] ch, int start, int length) throws SAXException {
content = String.copyValueOf(ch, start, length).trim();
}
}
class NeededInfo {
String id;
String firstName;
String lastName;
String location;
String organization_id;
String operator_id;
String device_id;
String dms_device_status;
String dms_current_message;
String last_comm_time;
String date;
String time;
public String toString() {
//return firstName + " " + lastName + "(" + id + ")" + location+date+time+device_name;
return "Organization id: " + organization_id + "\n" + "Operator id: " + operator_id + "\n" + "Device id: " + device_id + "\n"
+ "Dms Device Status: " + dms_device_status + "\n" + "Dms Current Message: " + dms_current_message + "\n" + "Last Comm Time" + "\n"
+ "Time: " + time + "\n" + "Date: " + date + "\n" + "decoded string is: " + "\n" + "-------------------------------------";
}
public void Read() {
byte[] byteArray = Base64.decodeBase64(dms_current_message.getBytes());
String decodedString = new String(byteArray);
System.out.print("The decoded message is: " + decodedString);
// return decodedString;
}
}
您的Read
方法訪問的dms_current_message
從未在問題中包含的所有代碼中初始化。
byte[] byteArray = Base64.decodeBase64(dms_current_message.getBytes());
很難猜測到哪里出了錯,但我在這里假設:
byte[] byteArray = Base64.decodeBase64(dms_current_message.getBytes());
我沒有看到dms_current_message
曾經被初始化過,但是您正在對其上調用一個方法,這肯定會導致null指針異常。
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