Java 字符串到长转换
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Java String to Long Conversion
提问by DaRoGa
Simple problem i know but I cannot see what is wrong. I have the following code:
我知道一个简单的问题，但我看不出哪里出了问题。我有以下代码：
String dxorderId = request.getParameter("orderid");
long orderid = Long.parseLong((dxorderId));
It is inside a servlet which is called from a PL/SQL procedure. The value of dxorderid is retrieved from a parameter in the URL of the page called. Therefore it seems to be treated as a string. So I must convert the string into a long. However, when I use the code above, I get the following error:
它位于从 PL/SQL 过程调用的 servlet 中。dxorderid 的值是从被调用页面的 URL 中的参数中检索到的。因此它似乎被视为一个字符串。所以我必须将字符串转换为长字符串。但是，当我使用上面的代码时，出现以下错误：
14-Nov-2013 13:07:41 org.apache.catalina.core.StandardWrapperValve invoke
SEVERE: Servlet.service() for servlet [com.zf.proceed.service.servlets.ViewOrderServlet] in context with path [/webapp] threw exception
java.lang.NumberFormatException: null
at java.lang.Long.parseLong(Long.java:372)
at java.lang.Long.parseLong(Long.java:461)
at com.zf.proceed.service.servlets.ViewOrderServlet.doRequest(ViewOrderServlet.java:28)
at com.zf.proceed.service.servlets.ProceedBaseServlet.doRequest(ProceedBaseServlet.java:106)
at com.zf.proceed.service.servlets.ProceedBaseServlet.doGet(ProceedBaseServlet.java:39)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:621)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:222)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:171)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:99)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:953)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:408)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1023)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:589)
at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:310)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
at java.lang.Thread.run(Thread.java:619)
I know it means that it cant be parsed but I dont Know why it cant. the value being input is 1454.
我知道这意味着它无法解析，但我不知道为什么它无法解析。输入的值为 1454。
采纳答案by christopher
I'm afraid the value is not 1454. The value is null, as evidenced by this line:
恐怕价值不是1454。值是null，正如这一行所证明的：
java.lang.NumberFormatException: null
You need to check your parameter name, and make sure you've got it right, including case and invisible characters.
您需要检查您的参数名称，并确保您输入正确，包括大小写和不可见字符。
回答by Ankur Shanbhag
Take a look at the exception closely : java.lang.NumberFormatException: null
仔细看看异常： java.lang.NumberFormatException: null
the above statement indicates that value for dxorderIdis null. Problem is with this line:
上面的语句表明值为dxorderId空。问题出在这一行：
String dxorderId = request.getParameter("orderid");
回答by Aniket Kulkarni
java.lang.NumberFormatException: null
If String dxorderIdis null then it will throw NumberFormatException
如果 StringdxorderId为 null 那么它会抛出 NumberFormatException
Solution
解决方案
Check dxorderIdis not nulland not empty string
检查dxorderId是不是null和不是empty string
if(dxorderId != null && !dxorderId.equals(""))
{
long orderid = Long.parseLong((dxorderId));
}
From oracle docs NumberFormatException
来自oracle 文档 NumberFormatException
public class NumberFormatException
extends IllegalArgumentException
Thrown to indicate that the application has attempted to convert a string to one of the numeric types, but that the string does not have the appropriate format.
抛出以指示应用程序已尝试将字符串转换为数字类型之一，但该字符串没有适当的格式。
回答by LionC
Well a NumberFormatExceptionmeans that the given Data can not be converted to a Longbecause it does not represent a Long-Value, so the problem lies at the source of the String, not in the Java Long-Parser.
嗯，aNumberFormatException意味着给定的 Data 不能转换为 a，Long因为它不代表一个Long-Value，所以问题出在 String 的来源，而不是 Java Long-Parser。
In your specific case the Parser states that the given value was null, so your request.getParameter("orderid");return null.
在您的特定情况下，解析器指出给定的值是null，因此您request.getParameter("orderid");返回null.
回答by Mikhail
Use createLongor toLongmethod from Apache's NumberUtils.
使用createLong或toLong从Apache的NumberUtils方法。
回答by MouseLearnJava
java.lang.NumberFormatException: null
java.lang.NumberFormatException: null
From the exception information, we can learn that dxorderidis nullwhich causes java.lang.NumberFormatException.
从异常信息中，我们可以了解到dxorderid为null导致java.lang.NumberFormatException.
Before parsing data, you need to check whether the value to be parsed is nullor emptyfirst .
在解析数据之前，需要先检查要解析的值是 null还是 空。
回答by Kamlesh Arya
error is due to this line.
错误是由于这一行。
String dxorderId = request.getParameter("orderid");
Check whether parameter name "orderid" is correct or not or ensure that its value is not null
检查参数名称“orderid”是否正确或确保其值不为空
