Properties file:

It is basically used to store data that is constant and can be used anywhere in the program.

Example: You can store the database credentials and connection parameters in the file and fetch it when required.

How to use:

PropertyPlaceholderConfigurer needs to be registered by the spring context to access the properties file. By adding the following snippet in the configuration file, bean registration is done automatically.

< context:property-placeholder
  location="classpath:[file-name].properties"
  />

Multiple properties file can also be included by adding the following:

< context:property-placeholder
  location="classpath:[file1-name].properties,classpath:[file2-name].properties"
  />

Property file needs to be in the same location of the other classes for using it this way.

Using the properties:

You can use the @Value annotation to fetch the values from the properties file.

syntax:

@Value("${property.value}")[access-specifier] [data-type] [field-name].

This will fetch the property from the file and insert it into the particular field specified.

Example:

Suppose we have jdbc.properties file with the content:

jdbc.username=root
jdbc.password=root

To get these values in the program we use the following steps:

1) Adding the code snippet in the xml configuration file

< context:property-placeholder
  location="classpath:jdbc.properties"
  />

2) Using @Value :

@Value("${jdbc.username}")private String userName;
@Value("${jdbc.password}")private String password;

userName and password will contain the values as 'root' as defined in the properties file.
These values can be used throughout the program after following the above steps.