Reading Properties file in Java

Question

I have the following code trying to read a properties file   Properties prop   new Properties    ClassLoader loader   Thread currentThread   getContextClassLoader               InputStream stream   loader getResourceAsStream  myProp properties    prop load stream     I get an exception at the last line  Specifically   Exception in thread  main  java lang NullPointerException at java util Properties LineReader readLine Properties java 418  at java util Properties load0 Properties java 337  at java util Properties load Properties java 325  at Assignment1 BaseStation readPropertyFile BaseStation java 46  at Assignment1 BaseStation main BaseStation java 87    thanks  Nikos

User · Answer

Your file should be available as com example foo myProps properties in classpath  Then load it as   props load this getClass   getResourceAsStream  myProps properties

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Properties prop   new Properties     try       prop load new FileInputStream  conf filename properties       catch  IOException e        e printStackTrace        conf filename properties base on project root dir

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For Reading Properties file with its original order       File file   new File     config edc properties        PropertiesConfiguration config   new PropertiesConfiguration        PropertiesConfigurationLayout layout   new PropertiesConfigurationLayout config       layout load new InputStreamReader new FileInputStream file          for Object propKey   layout getKeys             PropertiesConfiguration propval    layout getConfiguration            String value   propval getProperty  String  propKey  toString            out print  Current Key     propkey    Current Value     propval     lt br gt

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None of the current answers show the InputStream being closed  this will leak a file descriptor   and or don t deal with  getResourceAsStream   returning null when the resource is not found  this will lead to a NullPointerException with the confusing message   inStream parameter is null    You need something like the following   String propertiesFilename    server properties   Properties prop   new Properties    try  var inputStream   getClass   getClassLoader   getResourceAsStream propertiesFilename         if  inputStream    null            throw new FileNotFoundException propertiesFilename             prop load inputStream     catch  IOException e        throw new RuntimeException                   Could not read     propertiesFilename     resource file      e

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Make sure that the file name is correct and that the file is actually in the class path  getResourceAsStream   will return null if this is not the case which causes the last line to throw the exception   If myProp properties is in the root directory of your project  use  myProp properties instead

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You can use java io InputStream to read the file as shown below   InputStream inputStream   getClass   getClassLoader   getResourceAsStream myProps properties

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Given the context loader getResourceAsStream  myPackage myProp properties   should be used   Leading     doesn t work with ClassLoader getResourceAsStream String  method   Alternatively you could use Class getResourceAsStream String  method  which uses     to determine if the path is absolute or relative to the class location   Examples   myClass class getResourceAsStream  myProp properties   myClass class getResourceAsStream   myPackage myProp properties

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Specify the path starting from src as below   src main resources myprop proper

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I see that the question is an old one  If anyone stumbles upon this in the future  I think this is one simple way of doing it   Keep the properties file in your project folder           FileReader reader   new FileReader  Config properties             Properties prop   new Properties            prop load reader

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Many answers here describe dangerous methods where they instantiate a file input stream but do not get a reference to the input stream in order to close the stream later  This results in dangling input streams and memory leaks  The correct way of loading the properties should be similar to following       Properties prop   new Properties        try InputStream fis   new FileInputStream  myProp properties              prop load fis             catch Exception e            System out println  Unable to find the specified properties file            e printStackTrace            return          Note the instantiating of the file input stream in try-with-resources block  Since a FileInputStream is autocloseable  it will be automatically closed after the try-with-resources block is exited  If you want to use a simple try block  you must explicitly close it using fis close    in the finally block

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You can t use this keyword like -   props load this getClass   getResourceAsStream  myProps properties       in a static context   The best thing would be to get hold of application context like -   ApplicationContext context   new ClassPathXmlApplicationContext  classpath  META-INF spring app-context xml      then you can load the resource file from the classpath -     load a properties file from class path  inside static method         prop load context getClassLoader   getResourceAsStream  config properties       This will work for both static and non static context and the best part is this properties file can be in any package folder included in the application s classpath

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Based on your exception  the InputStream is null  this means the class loader is not finding your properties file  I m guessing that myProp properties is in the root of your project  if that s the case  you need a preceding slash   InputStream stream   loader getResourceAsStream   myProp properties

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If your properties file path and your java class path are same then you should this  For example   src myPackage MyClass java src myPackage MyFile properties  Properties prop   new Properties    InputStream stream   MyClass class getResourceAsStream  quot MyFile properties quot    prop load stream

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You can use ResourceBundle class to read the properties file   ResourceBundle rb   ResourceBundle getBundle  myProp properties

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You can find information on this page  http   www mkyong com java java-properties-file-examples   Properties prop   new Properties    try         load a properties file from class path  inside static method     prop load App class getClassLoader   getResourceAsStream  config properties            get the property value and print it out     System out println prop getProperty  database         System out println prop getProperty  dbuser         System out println prop getProperty  dbpassword         catch  IOException ex        ex printStackTrace

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if your config properties is not in src main resource directory and it is in root directory of the project then you need to do somethinglike below  -   Properties prop   new Properties              File configFile   new File myProp properties   InputStream stream   new FileInputStream configFile   prop load stream

[java] Reading Properties file in Java

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