Using Regular Expressions to Extract a Value in Java

Question

I have several strings in the rough form    some text   some number   some more text    I want to extract the text in  some number  using the Java Regex classes   I know roughly what regular expression I want to use  though all suggestions are welcome   What I m really interested in are the Java calls to take the regex string and use it on the source data to produce the value of  some number    EDIT  I should add that I m only interested in a single  some number   basically  the first instance   The source strings are short and I m not going to be looking for multiple occurrences of  some number

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if you are reading from file then this can help you                try               InputStream inputStream    InputStream  mnpMainBean getUploadedBulk   getInputStream                 BufferedReader br   new BufferedReader new InputStreamReader inputStream                 String line                 Ref 03              while   line   br readLine       null                    if  line matches   A-Z    d    d    2    s   d      d                               String   splitRecord   line split                              do something                                     else                       br close                           error                      return                                                    br close                                        catch  IOException  ioExpception                logger logDebug  Exception     ioExpception getStackTrace

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Simple Solution     Regexplanation             beginning of line      D     1  non-digit characters       d    1  digit characters in a capture group            0  any character String regexStr       D    d           Compile the regex String into a Pattern Pattern p   Pattern compile regexStr       Create a matcher with the input String Matcher m   p matcher inputStr       If we find a match if  m find             Get the String from the first capture group     String someDigits   m group 1             do something with someDigits     Solution in a Util Class  public class MyUtil       private static Pattern pattern   Pattern compile     D    d            private static Matcher matcher   pattern matcher              Assumptions  inputStr is a non-null String     public static String extractFirstNumber String inputStr              Reset the matcher with a new input String         matcher reset inputStr               Check if there s a match         if matcher find                    Return the number  in the first capture group              return matcher group 1            else                 Return some default value  if there is no match             return null                             Use the util function and print out the result String firstNum   MyUtil extractFirstNumber  Testing4234Things    System out println firstNum

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import java util regex Matcher  import java util regex Pattern   public class Regex1       public static void main String  args            Pattern p   Pattern compile    d             Matcher m   p matcher  hello1234goodboy789very2345            while m find                  System out println m group                         Output   1234 789 2345

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In Java 1 4 and up   String input          Matcher matcher   Pattern compile    0-9    0-9     0-9     matcher input   if  matcher find          String someNumberStr   matcher group 1          if you need this to be an int      int someNumberInt   Integer parseInt someNumberStr

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Try doing something like this   Pattern p   Pattern compile        d        Matcher m   p matcher  Testing123Testing     if  m find          System out println m group 1

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Full example   private static final Pattern p   Pattern compile     a-zA-Z     0-9           public static void main String   args           create matcher for pattern p and given string     Matcher m   p matcher  Testing123Testing            if an occurrence if a pattern was found in a given string        if  m find                    then you can use group   methods          System out println m group 0       whole matched expression         System out println m group 1       first expression from round brackets  Testing          System out println m group 2       second one  123          System out println m group 3       third one  Testing            Since you re looking for the first number  you can use such regexp     D   d       and m group 1  will return you the first number  Note that signed numbers can contain a minus sign     D  -  d

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In Java 1 4 and up   String input          Matcher matcher   Pattern compile    0-9    0-9     0-9     matcher input   if  matcher find          String someNumberStr   matcher group 1          if you need this to be an int      int someNumberInt   Integer parseInt someNumberStr

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Allain basically has the java code  so you can use that  However  his expression only matches if your numbers are only preceded by a stream of word characters        d      should be able to find the first string of digits  You don t need to specify what s before it  if you re sure that it s going to be the first string of digits  Likewise  there is no use to specify what s after it  unless you want that  If you just want the number  and are sure that it will be the first string of one or more digits then that s all you need    If you expect it to be offset by spaces  it will make it even more distinct to specify      s    d    s     might be better    If you need all three parts  this will do       D     d          EDIT The Expressions given by Allain and Jack suggest that you need to specify some subset of non-digits in order to capture digits  If you tell the regex engine you re looking for  d then it s going to ignore everything before the digits  If J or A s expression fits your pattern  then the whole match equals the input string  And there s no reason to specify it  It probably slows a clean match down  if it isn t totally ignored

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Look you can do it using StringTokenizer   String str    as   123  as   234  as   345  StringTokenizer st   new StringTokenizer str  as      while st hasMoreTokens        String k   st nextToken          you will get first numeric data i e 123   int kk   Integer parseInt k     System out println  k string token in integer            kk      String k1   st nextToken          you will get second numeric data i e 234   int kk1   Integer parseInt k1     System out println  new string k1 token in integer        kk1      String k2   st nextToken          you will get third numeric data i e 345   int kk2   Integer parseInt k2     System out println  k2 string token is in integer         kk2       Since we are taking these numeric data into three different variables we can use this data anywhere in the code  for further use

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In addition to Pattern  the Java String class also has several methods that can work with regular expressions  in your case the code will be    ab123abc  replaceFirst    D    d         1     where   D is a non-digit character

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if you are reading from file then this can help you                try               InputStream inputStream    InputStream  mnpMainBean getUploadedBulk   getInputStream                 BufferedReader br   new BufferedReader new InputStreamReader inputStream                 String line                 Ref 03              while   line   br readLine       null                    if  line matches   A-Z    d    d    2    s   d      d                               String   splitRecord   line split                              do something                                     else                       br close                           error                      return                                                    br close                                        catch  IOException  ioExpception                logger logDebug  Exception     ioExpception getStackTrace

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Look you can do it using StringTokenizer   String str    as   123  as   234  as   345  StringTokenizer st   new StringTokenizer str  as      while st hasMoreTokens        String k   st nextToken          you will get first numeric data i e 123   int kk   Integer parseInt k     System out println  k string token in integer            kk      String k1   st nextToken          you will get second numeric data i e 234   int kk1   Integer parseInt k1     System out println  new string k1 token in integer        kk1      String k2   st nextToken          you will get third numeric data i e 345   int kk2   Integer parseInt k2     System out println  k2 string token is in integer         kk2       Since we are taking these numeric data into three different variables we can use this data anywhere in the code  for further use

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Allain basically has the java code  so you can use that  However  his expression only matches if your numbers are only preceded by a stream of word characters        d      should be able to find the first string of digits  You don t need to specify what s before it  if you re sure that it s going to be the first string of digits  Likewise  there is no use to specify what s after it  unless you want that  If you just want the number  and are sure that it will be the first string of one or more digits then that s all you need    If you expect it to be offset by spaces  it will make it even more distinct to specify      s    d    s     might be better    If you need all three parts  this will do       D     d          EDIT The Expressions given by Allain and Jack suggest that you need to specify some subset of non-digits in order to capture digits  If you tell the regex engine you re looking for  d then it s going to ignore everything before the digits  If J or A s expression fits your pattern  then the whole match equals the input string  And there s no reason to specify it  It probably slows a clean match down  if it isn t totally ignored

User · Answer

Try doing something like this   Pattern p   Pattern compile        d        Matcher m   p matcher  Testing123Testing     if  m find          System out println m group 1

User · Answer

Allain basically has the java code  so you can use that  However  his expression only matches if your numbers are only preceded by a stream of word characters        d      should be able to find the first string of digits  You don t need to specify what s before it  if you re sure that it s going to be the first string of digits  Likewise  there is no use to specify what s after it  unless you want that  If you just want the number  and are sure that it will be the first string of one or more digits then that s all you need    If you expect it to be offset by spaces  it will make it even more distinct to specify      s    d    s     might be better    If you need all three parts  this will do       D     d          EDIT The Expressions given by Allain and Jack suggest that you need to specify some subset of non-digits in order to capture digits  If you tell the regex engine you re looking for  d then it s going to ignore everything before the digits  If J or A s expression fits your pattern  then the whole match equals the input string  And there s no reason to specify it  It probably slows a clean match down  if it isn t totally ignored

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How about     d    0-9     s       0 1    s   0-9      I think it would take care of numbers with fractional part   I included white spaces and included   as possible separator  I m trying to get the numbers out of a string including floats and taking into account that the user might make a mistake and include white spaces while typing the number

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This function collect all matching sequences from string  In this example it takes all email addresses from string   static final String EMAIL PATTERN      A-Za-z0-9-           A-Za-z0-9-                   A-Za-z0-9-       A-Za-z0-9         A-Za-z  2       public List lt String gt  getAllEmails String message              List lt String gt  result   null      Matcher matcher   Pattern compile EMAIL PATTERN  matcher message        if  matcher find              result   new ArrayList lt String gt             result add matcher group              while  matcher find                  result add matcher group                          return result      For message    adf gmail com   lt another osiem osiem gt  gt  gt  gt  lalala aaa pl  it will create List of 3 elements

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Sometimes you can use simple  split  REGEXP   method available in java lang String  For example   String input    first second third      To retrieve  first   input split      0     second input split      1    third input split      2

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Full example   private static final Pattern p   Pattern compile     a-zA-Z     0-9           public static void main String   args           create matcher for pattern p and given string     Matcher m   p matcher  Testing123Testing            if an occurrence if a pattern was found in a given string        if  m find                    then you can use group   methods          System out println m group 0       whole matched expression         System out println m group 1       first expression from round brackets  Testing          System out println m group 2       second one  123          System out println m group 3       third one  Testing            Since you re looking for the first number  you can use such regexp     D   d       and m group 1  will return you the first number  Note that signed numbers can contain a minus sign     D  -  d

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In Java 1 4 and up   String input          Matcher matcher   Pattern compile    0-9    0-9     0-9     matcher input   if  matcher find          String someNumberStr   matcher group 1          if you need this to be an int      int someNumberInt   Integer parseInt someNumberStr

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This function collect all matching sequences from string  In this example it takes all email addresses from string   static final String EMAIL PATTERN      A-Za-z0-9-           A-Za-z0-9-                   A-Za-z0-9-       A-Za-z0-9         A-Za-z  2       public List lt String gt  getAllEmails String message              List lt String gt  result   null      Matcher matcher   Pattern compile EMAIL PATTERN  matcher message        if  matcher find              result   new ArrayList lt String gt             result add matcher group              while  matcher find                  result add matcher group                          return result      For message    adf gmail com   lt another osiem osiem gt  gt  gt  gt  lalala aaa pl  it will create List of 3 elements

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Simple Solution     Regexplanation             beginning of line      D     1  non-digit characters       d    1  digit characters in a capture group            0  any character String regexStr       D    d           Compile the regex String into a Pattern Pattern p   Pattern compile regexStr       Create a matcher with the input String Matcher m   p matcher inputStr       If we find a match if  m find             Get the String from the first capture group     String someDigits   m group 1             do something with someDigits     Solution in a Util Class  public class MyUtil       private static Pattern pattern   Pattern compile     D    d            private static Matcher matcher   pattern matcher              Assumptions  inputStr is a non-null String     public static String extractFirstNumber String inputStr              Reset the matcher with a new input String         matcher reset inputStr               Check if there s a match         if matcher find                    Return the number  in the first capture group              return matcher group 1            else                 Return some default value  if there is no match             return null                             Use the util function and print out the result String firstNum   MyUtil extractFirstNumber  Testing4234Things    System out println firstNum

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Full example   private static final Pattern p   Pattern compile     a-zA-Z     0-9           public static void main String   args           create matcher for pattern p and given string     Matcher m   p matcher  Testing123Testing            if an occurrence if a pattern was found in a given string        if  m find                    then you can use group   methods          System out println m group 0       whole matched expression         System out println m group 1       first expression from round brackets  Testing          System out println m group 2       second one  123          System out println m group 3       third one  Testing            Since you re looking for the first number  you can use such regexp     D   d       and m group 1  will return you the first number  Note that signed numbers can contain a minus sign     D  -  d

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How about     d    0-9     s       0 1    s   0-9      I think it would take care of numbers with fractional part   I included white spaces and included   as possible separator  I m trying to get the numbers out of a string including floats and taking into account that the user might make a mistake and include white spaces while typing the number

User · Answer

Full example   private static final Pattern p   Pattern compile     a-zA-Z     0-9           public static void main String   args           create matcher for pattern p and given string     Matcher m   p matcher  Testing123Testing            if an occurrence if a pattern was found in a given string        if  m find                    then you can use group   methods          System out println m group 0       whole matched expression         System out println m group 1       first expression from round brackets  Testing          System out println m group 2       second one  123          System out println m group 3       third one  Testing            Since you re looking for the first number  you can use such regexp     D   d       and m group 1  will return you the first number  Note that signed numbers can contain a minus sign     D  -  d

User · Answer

Allain basically has the java code  so you can use that  However  his expression only matches if your numbers are only preceded by a stream of word characters        d      should be able to find the first string of digits  You don t need to specify what s before it  if you re sure that it s going to be the first string of digits  Likewise  there is no use to specify what s after it  unless you want that  If you just want the number  and are sure that it will be the first string of one or more digits then that s all you need    If you expect it to be offset by spaces  it will make it even more distinct to specify      s    d    s     might be better    If you need all three parts  this will do       D     d          EDIT The Expressions given by Allain and Jack suggest that you need to specify some subset of non-digits in order to capture digits  If you tell the regex engine you re looking for  d then it s going to ignore everything before the digits  If J or A s expression fits your pattern  then the whole match equals the input string  And there s no reason to specify it  It probably slows a clean match down  if it isn t totally ignored

User · Answer

In addition to Pattern  the Java String class also has several methods that can work with regular expressions  in your case the code will be    ab123abc  replaceFirst    D    d         1     where   D is a non-digit character

User · Answer

Pattern p   Pattern compile     D     d          Matcher m   p matcher  this is your number 1234 thank you    if  m find          String someNumberStr   m group 2       int someNumberInt   Integer parseInt someNumberStr

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import java util regex Matcher  import java util regex Pattern   public class Regex1       public static void main String  args            Pattern p   Pattern compile    d             Matcher m   p matcher  hello1234goodboy789very2345            while m find                  System out println m group                         Output   1234 789 2345

User · Answer

Sometimes you can use simple  split  REGEXP   method available in java lang String  For example   String input    first second third      To retrieve  first   input split      0     second input split      1    third input split      2

User · Answer

In Java 1 4 and up   String input          Matcher matcher   Pattern compile    0-9    0-9     0-9     matcher input   if  matcher find          String someNumberStr   matcher group 1          if you need this to be an int      int someNumberInt   Integer parseInt someNumberStr

User · Answer

Pattern p   Pattern compile     D     d          Matcher m   p matcher  this is your number 1234 thank you    if  m find          String someNumberStr   m group 2       int someNumberInt   Integer parseInt someNumberStr

[java] Using Regular Expressions to Extract a Value in Java

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