![](/img/trans.png)
[英]java String != null not working reading from bufferedReader
[英]Java BufferedReader receives null string
我的程序布局合理,以便主应用程序可以将命令发送到与其连接的任何节点。 当节点接收到请求时,它将返回响应并继续等待更多请求。
运行该应用程序时,该节点会成功回复一个请求,而发送第二个请求时,该节点会将其视为空值或根本看不到它。 为什么这种情况不断发生?
PS我希望与该节点的连接保持打开状态,以便它可以接收更多请求。
请求发送代码:
public java.lang.String getTime(server.Node node){
protocol.Message ms = new protocol.Message("<time>","");
node.sendRequestToClient(ms);
node.dos.flush();
java.lang.System.out.println("Sent time request to " + node.ip);
java.lang.String time = null;
try {
time = node.dis.readLine();
} catch (java.io.IOException ex) {
System.out.println("Could not read response.");
}
protocol.Message response = protocol.Message.parseDataToMessage(time);
java.lang.String systime = response.getActionData();
return systime;
}
响应发送代码:
public class Client {
public Client(NetworkConnection connection){
this.connectionToServer = connection;
try{
connectionToServer.connect();
responseOutStream = connectionToServer.getPrintWriter();
requestInStream = connectionToServer.getBufferedReader();
}catch(IOException ex){
System.out.println("Could not connect to server." + ex.getMessage() + ex.toString());
}
}
public void beginRequestListener(){
String request;
try {
while((request = requestInStream.readLine())!=""){
System.out.println("Recieved request: " + request + request.length());
Message response = Message.parseDataToMessage(request);
sendResponseToServer(response);
}
} catch (java.io.IOException ex) {
System.out.println("Could not read request stream.");
} catch(NullPointerException e){
e.printStackTrace();
e.getClass();
}
}
public void sendResponseToServer(Message ms){
protocol.Message response = MessageParser.compileResponse(ms);
java.lang.System.out.println("Response to send: "+response);
response.send(responseOutStream);
}
public BufferedReader requestInStream;
public PrintWriter responseOutStream;
public NetworkConnection connectionToServer;
}
MessageParser类:
public class MessageParser {
static public Message compileResponse(Message ms){
Message response = null;
switch(ms.getAction()){
case "<time>":
response = new Message("<time>", String.valueOf(System.currentTimeMillis()));
break;
case "<date>":
SimpleDateFormat sd = new SimpleDateFormat("yyyy.MM.dd G 'at' HH:mm:ss z");
Date date = new Date();
sd.setTimeZone(TimeZone.getTimeZone("IST"));
response = new Message("<date>", date.toString());
break;
default:
break;
}
return response;
}
}
堆栈跟踪和输出:
Recieved request: <action><time><action><actionData><actionData>
Response to send: <action><time><action><actionData>1370380854566<actionData>
Recieved request:
java.lang.NullPointerException
at protocol.MessageParser.compileResponse(MessageParser.java:23)
at client.Client.sendResponseToServer(Client.java:67)
at client.Client.beginRequestListener(Client.java:52)
at client.ClientInterface.main(ClientInterface.java:107)
讯息类别:
公共类消息{
public Message(String data){
}
public Message(String action, String actionData){
this.action = action;
this.actionData = actionData;
}
public void send(PrintWriter connection){
try{
connection.println(this.toString());
connection.flush();
//System.out.println(this.toString());
}catch(Exception ex){
System.out.println("Could not send Message.");
}
}
@java.lang.Override
public String toString(){
return
action_marker + action + action_marker +
actionData_marker + actionData + actionData_marker +
eof_marker;
}
public static Message parseDataToMessage(String data){
Message ms = null;
if(data.isEmpty() == false){
int begin_action_marker = data.indexOf("<action>")+8;
int end_action_marker = data.lastIndexOf("<action>");
String action = data.substring(begin_action_marker, end_action_marker);
int begin_actionData_marker = data.indexOf("<actionData>")+12;
int end_actionData_marker = data.lastIndexOf("<actionData>");
String actionData = data.substring(begin_actionData_marker, end_actionData_marker);
ms = new Message(action, actionData);
}
return ms;
}
public void setAction(String action){
this.action = action;
}
public String getActionData(){
return actionData;
}
public String getAction(){
return action;
}
public void setActionData(String action){
this.actionData = action;
}
public String eof_marker = "\r\n";
public String action;
public String action_marker = "<action>";
public String actionData;
public String actionData_marker = "<actionData>";
}
我猜:
(request = requestInStream.readLine())
收到一个空请求 Message.parseDataToMessage(request);
对于空请求返回null
compileResponse
中生成NullPointerException (可能)解决方案:更改此
while((request = requestInStream.readLine())!=""){
到这个:
while(!(request = requestInStream.readLine()).isEmpty())
为什么您的代码不起作用: 如何比较Java中的字符串?
while((request = requestInStream.readLine())!=“”){
这个测试是做什么用的? 您是否期待空的请求? 你不应该这样 如果您发现其中一个,则说明发送方存在错误。
但是,在执行其他操作之前,必须测试readLine()
的结果是否为null。 该行应显示为:
while((request = requestInStream.readLine())!= null){
声明:本站的技术帖子网页,遵循CC BY-SA 4.0协议,如果您需要转载,请注明本站网址或者原文地址。任何问题请咨询:yoyou2525@163.com.