问题
I'm guessing I'm getting this error because the string is trying to substring a null value. But wouldn't the ".length() > 0" part eliminate that issue?
Here is the Java snippet:
if (itemdescription.length() > 0) {
pstmt2.setString(3, itemdescription.substring(0,38));
}
else {
pstmt2.setString(3, "_");
}
I got this error:
java.lang.StringIndexOutOfBoundsException: String index out of range: 38
at java.lang.String.substring(Unknown Source)
at MASInsert2.itemimport(MASInsert2.java:192)
at MASInsert2.processRequest(MASInsert2.java:125)
at MASInsert2.doGet(MASInsert2.java:219)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:627)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:269)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:188)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:213)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:172)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:117)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:108)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:174)
at org.apache.coyote.http11.Http11AprProcessor.process(Http11AprProcessor.java:835)
at org.apache.coyote.http11.Http11AprProtocol$Http11ConnectionHandler.process(Http11AprProtocol.java:640)
at org.apache.tomcat.util.net.AprEndpoint$Worker.run(AprEndpoint.java:1286)
at java.lang.Thread.run(Unknown Source)
回答1:
I"m guessing i'm getting this error because the string is trying to substring a Null value. But wouldn't the ".length() > 0" part eliminate that issue?
No, calling itemdescription.length() when itemdescription is null would not generate a StringIndexOutOfBoundsException, but rather a NullPointerException since you would essentially be trying to call a method on null.
As others have indicated, StringIndexOutOfBoundsException indicates that itemdescription is not at least 38 characters long. You probably want to handle both conditions (I assuming you want to truncate):
final String value;
if (itemdescription == null || itemdescription.length() <= 0) {
value = "_";
} else if (itemdescription.length() <= 38) {
value = itemdescription;
} else {
value = itemdescription.substring(0, 38);
}
pstmt2.setString(3, value);
Might be a good place for a utility function if you do that a lot...
回答2:
It is a pity that substring is not implemented in a way that handles short strings – like in other languages e.g. Python.
Ok, we cannot change that and have to consider this edge case every time we use substr, instead of if-else clauses I would go for this shorter variant:
myText.substring(0, Math.min(6, myText.length()))
回答3:
You really need to check if the string's length is greater to or equal to 38.
回答4:
I would recommend apache commons lang. A one-liner takes care of the problem.
pstmt2.setString(3, StringUtils.defaultIfEmpty(
StringUtils.subString(itemdescription,0, 38), "_"));
回答5:
substring(0,38) means the String has to be 38 characters or longer. If not, the "String index is out of range".
回答6:
if (itemdescription != null && itemdescription.length() > 0) {
pstmt2.setString(3, itemdescription.substring(0, Math.min(itemdescription.length(), 38)));
} else {
pstmt2.setString(3, "_");
}
回答7:
I'm assuming your column is 38 characters in length, so you want to truncate itemdescription to fit within the database. A utility function like the following should do what you want:
/**
* Truncates s to fit within len. If s is null, null is returned.
**/
public String truncate(String s, int len) {
if (s == null) return null;
return s.substring(0, Math.min(len, s.length()));
}
then you just call it like so:
String value = "_";
if (itemdescription != null && itemdescription.length() > 0) {
value = truncate(itemdescription, 38);
}
pstmt2.setString(3, value);
回答8:
Java's substring method fails when you try and get a substring starting at an index which is longer than the string.
An easy alternative is to use Apache Commons StringUtils.substring:
public static String substring(String str, int start)
Gets a substring from the specified String avoiding exceptions.
A negative start position can be used to start n characters from the end of the String.
A null String will return null. An empty ("") String will return "".
StringUtils.substring(null, *) = null
StringUtils.substring("", *) = ""
StringUtils.substring("abc", 0) = "abc"
StringUtils.substring("abc", 2) = "c"
StringUtils.substring("abc", 4) = ""
StringUtils.substring("abc", -2) = "bc"
StringUtils.substring("abc", -4) = "abc"
Parameters:
str - the String to get the substring from, may be null
start - the position to start from, negative means count back from the end of the String by this many characters
Returns:
substring from start position, null if null String input
Note, if you can't use Apache Commons lib for some reason, you could just grab the parts you need from the source
// Substring
//-----------------------------------------------------------------------
/**
* <p>Gets a substring from the specified String avoiding exceptions.</p>
*
* <p>A negative start position can be used to start {@code n}
* characters from the end of the String.</p>
*
* <p>A {@code null} String will return {@code null}.
* An empty ("") String will return "".</p>
*
* <pre>
* StringUtils.substring(null, *) = null
* StringUtils.substring("", *) = ""
* StringUtils.substring("abc", 0) = "abc"
* StringUtils.substring("abc", 2) = "c"
* StringUtils.substring("abc", 4) = ""
* StringUtils.substring("abc", -2) = "bc"
* StringUtils.substring("abc", -4) = "abc"
* </pre>
*
* @param str the String to get the substring from, may be null
* @param start the position to start from, negative means
* count back from the end of the String by this many characters
* @return substring from start position, {@code null} if null String input
*/
public static String substring(final String str, int start) {
if (str == null) {
return null;
}
// handle negatives, which means last n characters
if (start < 0) {
start = str.length() + start; // remember start is negative
}
if (start < 0) {
start = 0;
}
if (start > str.length()) {
return EMPTY;
}
return str.substring(start);
}
回答9:
itemdescription is shorter than 38 chars. Which is why the StringOutOfBoundsException is being thrown.
Checking .length() > 0 simply makes sure the String has some not-null value, what you need to do is check that the length is long enough. You could try:
if(itemdescription.length() > 38)
...
回答10:
You must check the String length. You assume that you can do substring(0,38) as long as String is not null, but you actually need the String to be of at least 38 characters length.
回答11:
When this is appropriate, I use matches instead of substring.
With substring:
if( myString.substring(1,17).equals("Someting I expect") ) {
// Do stuff
}
// Does NOT work if myString is too short
With matches (must use Regex notation):
if( myString.matches("Someting I expect.*") ) {
// Do stuff
}
// This works with all strings
回答12:
You get this if itemdescription is shorter than 38 characters
You can look which exceptions are thrown and when in the JAVA API in you case for String#substring(int,int): https://docs.oracle.com/javase/9/docs/api/java/lang/String.html#substring-int-int-
substring public String substring(int beginIndex, int endIndex) . . . Throws: IndexOutOfBoundsException if the beginIndex is negative, or endIndex is larger than the length of this String object, or beginIndex is larger than endIndex. (same applies to previous java versions as well)
来源：https://stackoverflow.com/questions/953527/java-substring-string-index-out-of-range