Named placeholders in string formatting

Question

In Python  when formatting string  I can fill placeholders by name rather than by position  like that   print  There s an incorrect value    value s  in column     column d           value   x   column   y     I wonder if that is possible in Java  hopefully  without external libraries

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not quite  but you can use MessageFormat to reference one value multiple times   MessageFormat format  There s an incorrect value    0    in column    1    x  y     The above can be done with String format   as well  but I find messageFormat syntax cleaner if you need to build complex expressions  plus you dont need to care about the type of the object you are putting into the string

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Another example of Apache Common StringSubstitutor for simple named placeholder   String template    Welcome to  theWorld   My name is  myName      Map lt String  String gt  values   new HashMap lt  gt     values put  theWorld    Stackoverflow    values put  myName    Thanos     String message   StringSubstitutor replace template  values              System out println message       Welcome to Stackoverflow  My name is Thanos

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This is an old thread  but just for the record  you could also use Java 8 style  like this   public static String replaceParams Map lt String  String gt  hashMap  String template        return hashMap entrySet   stream   reduce template   s  e  - gt  s replace        e getKey          e getValue                  s  s2  - gt  s       Usage   public static void main String   args        final HashMap lt String  String gt  hashMap   new HashMap lt String  String gt                            put  foo    foo1                put  bar    bar1                put  car    BMW                put  truck    MAN                         String res   replaceParams hashMap   This is    foo   and    foo    but also    bar      bar   indeed         System out println res       System out println replaceParams hashMap   This is    car   and    foo    but also    bar      bar   indeed          System out println replaceParams hashMap   This is    car   and    truck    but also    foo      bar        truck   indeed          The output will be   This is  foo1  and  foo1   but also  bar1   bar1  indeed  This is  BMW  and  foo1   but also  bar1   bar1  indeed  This is  BMW  and  MAN   but also  foo1   bar1     MAN  indeed

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There is nothing built into Java at the moment of writing this  I would suggest writing your own implementation  My preference is for a simple fluent builder interface instead of creating a map and passing it to function -- you end up with a nice contiguous chunk of code  for example   String result   new TemplatedStringBuilder  My name is   name   and I from   town         replace  name    John Doe       replace  town    Sydney       finish      Here is a simple implementation   class TemplatedStringBuilder        private final static String TEMPLATE START TOKEN             private final static String TEMPLATE CLOSE TOKEN              private final String template      private final Map lt String  String gt  parameters   new HashMap lt  gt          public TemplatedStringBuilder String template            if  template    null  throw new NullPointerException            this template   template             public TemplatedStringBuilder replace String key  String value           parameters put key  value           return this             public String finish             StringBuilder result   new StringBuilder             int startIndex   0           while  startIndex  lt  template length                  int openIndex    template indexOf TEMPLATE START TOKEN  startIndex                if  openIndex  lt  0                   result append template substring startIndex                    break                             int closeIndex   template indexOf TEMPLATE CLOSE TOKEN  openIndex                if closeIndex  lt  0                   result append template substring startIndex                    break                             String key   template substring openIndex   TEMPLATE START TOKEN length    closeIndex                if   parameters containsKey key   throw new RuntimeException  missing value for key      key                result append template substring startIndex  openIndex                result append parameters get key                 startIndex   closeIndex   TEMPLATE CLOSE TOKEN length                       return result toString

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I am the author of a small library that does exactly what you want   Student student   new Student  Andrei   30   Male     String studStr   template    id  tName    st getName   Age    st getAge   Gender    st getGender                         arg  id   10                       arg  st   student                       format    System out println studStr     Or you can chain the arguments   String result   template    x      y      z                         args  x   5   y   10   z   15                       format    System out println result       Output   5   10   15

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StrSubstitutor of jakarta commons lang is a light weight way of doing this provided your values are already formatted correctly    http   commons apache org proper commons-lang javadocs api-3 1 org apache commons lang3 text StrSubstitutor html  Map lt String  String gt  values   new HashMap lt String  String gt     values put  value   x   values put  column   y   StrSubstitutor sub   new StrSubstitutor values              String result   sub replace  There s an incorrect value    value   in column     column       The above results in    There s an incorrect value  1  in column   2   When using Maven you can add this dependency to your pom xml    lt dependency gt       lt groupId gt org apache commons lt  groupId gt       lt artifactId gt commons-lang3 lt  artifactId gt       lt version gt 3 4 lt  version gt   lt  dependency gt

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You can use StringTemplate library  it offers what you want and much more   import org antlr stringtemplate     final StringTemplate hello   new StringTemplate  Hello   name     hello setAttribute  name    World    System out println hello toString

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There is Java Plugin to use string interpolation in Java  like in Kotlin  JavaScript   Supports Java 8  9  10  11     https   github com antkorwin better-strings  Using variables in string literals   int a   3  int b   4  System out println    a      b      a b       Using expressions   int a   3  int b   4  System out println  pow     a   a     System out println  flag     a  gt  b   true   false       Using functions    Test void functionCall         System out println  fact 5      factorial 5         long factorial int n        long fact   1      for  int i   2  i  lt   n  i              fact   fact   i            return fact      For more info  please read the project README

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Thanks for all your help  Using all your clues  I ve written routine to do exactly what I want -- python-like string formatting using dictionary  Since I m Java newbie  any hints are appreciated   public static String dictFormat String format  Hashtable lt String  Object gt  values        StringBuilder convFormat   new StringBuilder format       Enumeration lt String gt  keys   values keys        ArrayList valueList   new ArrayList        int currentPos   1      while  keys hasMoreElements              String key   keys nextElement            formatKey          key                formatPos         Integer toString currentPos                 int index   -1          while   index   convFormat indexOf formatKey  index      -1                convFormat replace index  index   formatKey length    formatPos               index    formatPos length                      valueList add values get key              currentPos            return String format convFormat toString    valueList toArray

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You should have a look at the official ICU4J library  It provides a MessageFormat class similar to the one available with the JDK but this former supports named placeholders    Unlike other solutions provided on this page  ICU4j is part of the ICU project that is maintained by IBM and regularly updated  In addition  it supports advanced use cases such as pluralization and much more     Here is a code example   MessageFormat messageFormat           new MessageFormat  Publication written by  author       Map lt String  String gt  args   Map of  author    John Doe     System out println messageFormat format args

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Try Freemarker  templating library

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Apache Commons Lang s replaceEach method may come in handy dependeding on your specific needs  You can easily use it to replace placeholders by name with this single method call   StringUtils replaceEach  There s an incorrect value    value   in column     column                new String        value       column      new String     x  y       Given some input text  this will replace all occurrences of the placeholders in the first string array with the corresponding values in the second one

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https   dzone com articles java-string-format-examples String format inputString   listOfParams   would be the easiest way  Placeholders in string can be defined by order  For more details check the provided link

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I tried in just a quick way public static void main String   args         String rowString    quot replace the value   var1  with   var2  quot            Map lt String String gt  mappedValues   new HashMap lt  gt              mappedValues put  quot var1 quot    quot Value 1 quot        mappedValues put  quot var2 quot    quot Value 2 quot             System out println replaceOccurence rowString  mappedValues       private static  String replaceOccurence String baseStr  Map lt String String gt  mappedValues        for String key  mappedValues keySet                  baseStr   baseStr replace  quot    quot  key  quot   quot   mappedValues get key                   return baseStr

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I created also a util helper class  using jdk 8  which can format a string an replaces occurrences of variables   For this purpose I used the Matchers  appendReplacement  method which does all the substitution and loops only over the affected parts of a format string   The helper class isn t currently well javadoc documented  I will changes this in the future    Anyway I commented the most important lines  I hope         public class FormatHelper          Prefix and suffix for the enclosing variable name in the format string        Replace the default values with any you need      public static final String DEFAULT PREFIX             public static final String DEFAULT SUFFIX               Define dynamic function what happens if a key is not found        Replace the defualt exception with any  unchecked  exception type you need or any other behavior      public static final BiFunction lt String  String  String gt  DEFAULT NO KEY FUNCTION                fullMatch  variableName  - gt                    throw new RuntimeException String format  Key   s for variable  s not found                                                             variableName                                                           fullMatch                       private final Pattern variablePattern      private final Map lt String  String gt  values      private final BiFunction lt String  String  String gt  noKeyFunction      private final String prefix      private final String suffix       public FormatHelper Map lt String  String gt  values            this DEFAULT NO KEY FUNCTION  values              public FormatHelper              BiFunction lt String  String  String gt  noKeyFunction  Map lt String  String gt  values            this DEFAULT PREFIX  DEFAULT SUFFIX  noKeyFunction  values              public FormatHelper String prefix  String suffix  Map lt String  String gt  values            this prefix  suffix  DEFAULT NO KEY FUNCTION  values              public FormatHelper              String prefix              String suffix              BiFunction lt String  String  String gt  noKeyFunction              Map lt String  String gt  values            this prefix   prefix          this suffix   suffix          this values   values          this noKeyFunction   noKeyFunction             Create the Pattern and quote the prefix and suffix so that the regex don t interpret special chars            The variable name is a   w   in an extra capture group          variablePattern   Pattern compile Pattern quote prefix        w      Pattern quote suffix               public static String format CharSequence format  Map lt String  String gt  values            return new FormatHelper values  format format              public static String format              CharSequence format              BiFunction lt String  String  String gt  noKeyFunction              Map lt String  String gt  values            return new FormatHelper noKeyFunction  values  format format              public static String format              String prefix  String suffix  CharSequence format  Map lt String  String gt  values            return new FormatHelper prefix  suffix  values  format format              public static String format              String prefix              String suffix              BiFunction lt String  String  String gt  noKeyFunction              CharSequence format              Map lt String  String gt  values            return new FormatHelper prefix  suffix  noKeyFunction  values  format format              public String format CharSequence format               Create matcher based on the init pattern for variable names          Matcher matcher   variablePattern matcher format              This buffer will hold all parts of the formatted finished string          StringBuffer formatBuffer   new StringBuffer               loop while the matcher finds another variable  prefix - gt  name  lt - suffix  match         while  matcher find                     The root capture group with the full match e g   variableName              String fullMatch   matcher group                   The capture group for the variable name resulting from    w    e g  variableName             String variableName   matcher group 1                  Get the value in our Map so the Key is the used variable name in our  format  string  The associated value will replace the variable                If key is missing  absent  call the noKeyFunction with parameters  fullMatch  and  variableName  else return the value              String value   values computeIfAbsent variableName  key - gt  noKeyFunction apply fullMatch  key                   Escape the Map value because the  appendReplacement  method interprets the   and   as special chars              String escapedValue   Matcher quoteReplacement value                  The  appendReplacement  method replaces the current  full  match  e g    variableName   with the value from the  values  Map                The replaced part of the  format  string is appended to the StringBuffer  formatBuffer               matcher appendReplacement formatBuffer  escapedValue                        The  appendTail  method appends the last part of the  format  String which has no regex match            That means if e g  our  format  string has no matches the whole untouched  format  string is appended to the StringBuffer  formatBuffer             Further more the method return the buffer          return matcher appendTail formatBuffer                         toString               public String getPrefix             return prefix             public String getSuffix             return suffix             public Map lt String  String gt  getValues             return values              You can create a class instance for a specific Map with values  or suffix prefix or noKeyFunction  like        Map lt String  String gt  values   new HashMap lt  gt         values put  firstName    Peter        values put  lastName    Parker          FormatHelper formatHelper   new FormatHelper values       formatHelper format    firstName    lastName  is Spiderman            Result   Peter Parker is Spiderman          Next format      formatHelper format  Does   firstName    lastName  works as photographer           Result   Does Peter Parker works as photographer      Further more you can define what happens if a key in the values Map is missing  works in both ways e g  wrong variable name in format string or missing key in Map   The default behavior is an thrown unchecked exception  unchecked because I use the default jdk8 Function which cant handle checked exceptions  like        Map lt String  String gt  map   new HashMap lt  gt         map put  firstName    Peter        map put  lastName    Parker          FormatHelper formatHelper   new FormatHelper map       formatHelper format    missingName    lastName  is Spiderman           Result  RuntimeException  Key  missingName for variable   missingName  not found     You can define a custom behavior in the constructor call like    Map lt String  String gt  values   new HashMap lt  gt     values put  firstName    Peter    values put  lastName    Parker      FormatHelper formatHelper   new FormatHelper fullMatch  variableName  - gt  variableName equals  missingName      John    SOMETHING WRONG   values   formatHelper format    missingName    lastName  is Spiderman        Result   John Parker is Spiderman      or delegate it back to the default no key behavior            FormatHelper formatHelper   new FormatHelper  fullMatch  variableName  - gt    variableName equals  missingName      John                FormatHelper DEFAULT NO KEY FUNCTION apply fullMatch                                                         variableName   map          For better handling there are also static method representations like    Map lt String  String gt  values   new HashMap lt  gt     values put  firstName    Peter    values put  lastName    Parker     FormatHelper format    firstName    lastName  is Spiderman    map      Result   Peter Parker is Spiderman

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public static String format String format  Map lt String  Object gt  values        StringBuilder formatter   new StringBuilder format       List lt Object gt  valueList   new ArrayList lt Object gt          Matcher matcher   Pattern compile           w      matcher format        while  matcher find              String key   matcher group 1            String formatKey   String format     s    key           int index   formatter indexOf formatKey            if  index    -1                formatter replace index  index   formatKey length      s                valueList add values get key                         return String format formatter toString    valueList toArray         Example   String format    My name is   1     0    1      Map lt String  Object gt  values   new HashMap lt String  Object gt     values put  0    James    values put  1    Bond     System out println format format  values       My name is Bond  James Bond

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For very simple cases you can simply use a hardcoded String replace  no need for a library there       String url    There s an incorrect value    value   in column     column        url   url replace    value    x      1     url   url replace    column    y      2   WARNING  I just wanted to show the simplest code possible  Of course DO NOT use this for serious production code where security matters  as stated in the comments  escaping  error handling and security are an issue here  But in the worst case you now know why using a  good  lib is required  -

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My answer is to   a  use StringBuilder when possible  b  keep  in any form  integer is the best  speciall char like dollar macro etc  position of  placeholder  and then use StringBuilder insert    few versions of arguments    Using external libraries seems overkill and I belive degrade performance significant  when StringBuilder is converted to String internally

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Based on the answer I created MapBuilder class   public class MapBuilder        public static Map lt String  Object gt  build Object    data            Map lt String  Object gt  result   new LinkedHashMap lt  gt              if  data length   2    0                throw new IllegalArgumentException  Odd number of arguments                       String key   null          Integer step   -1           for  Object value   data                step                switch  step   2                    case 0                      if  value    null                            throw new IllegalArgumentException  Null key value                                              key    String  value                      continue                  case 1                      result put key  value                       break                                   return result             then I created class StringFormat for String formatting   public final class StringFormat        public static String format String format  Object    args            Map lt String  Object gt  values   MapBuilder build args            for  Map Entry lt String  Object gt  entry   values entrySet                  String key   entry getKey                Object value   entry getValue                format   format replace       key  value toString                        return format             which you could use like that   String bookingDate   StringFormat format  From  startDate to  endDate               startDate   formattedStartDate             endDate   formattedEndDate

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You could have something like this on a string helper class         An interpreter for strings with named placeholders        For example given the string  hello   myName   and the map  lt code gt           lt p gt Map lt String  Object gt  map   new HashMap lt String  Object gt     lt  p gt           lt p gt map put  myName    world    lt  p gt      lt  code gt        the call   code format  hello   myName    map   returns  hello world        It replaces every occurrence of a named placeholder with its given value    in the map  If there is a named place holder which is not found in the    map then the string will retain that placeholder  Likewise  if there is    an entry in the map that does not have its respective placeholder  it is    ignored         param str               string to format     param values               to replace     return formatted string     public static String format String str  Map lt String  Object gt  values         StringBuilder builder   new StringBuilder str        for  Entry lt String  Object gt  entry   values entrySet               int start          String pattern          entry getKey                  String value   entry getValue   toString                Replace every occurence of   key  with value         while   start   builder indexOf pattern      -1                builder replace start  start   pattern length    value                        return builder toString

[java] Named placeholders in string formatting

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