How do you escape colon (:) in Properties file?

We hit this question a couple of days ago. We were manipulating existing properties files with URLs as values.

It's risky but if your property values are less than 40 characters then you can use the "list" method instead of "store":

http://docs.oracle.com/javase/6/docs/api/java/util/Properties.html#list(java.io.PrintWriter)

We had a quick look at the JDK code and hacked out a custom implementation of store that works for our purposes:

public void store(Properties props, String propertyFilePath) throws FileNotFoundException {
    PrintWriter pw = new PrintWriter(propertyFilePath); 
    for (Enumeration e = props.propertyNames(); e.hasMoreElements();) {
        String key = (String) e.nextElement();
        pw.println(key + "=" + props.getProperty(key));
    }
    pw.close();
}

I came across the same issue. Forward slashes / also get escaped by the store() method in Properties.

I solved this issue by creating my own CustomProperties class (extending java.util.Properties) and commenting out the call to saveConvert() in the customStore0() method.

Here is my CustomProperties class:

import java.io.BufferedWriter;
import java.io.IOException;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.util.Date;
import java.util.Enumeration;
import java.util.Properties;

public class CustomProperties extends Properties {
  private static final long serialVersionUID = 1L;
  @Override
  public void store(OutputStream out, String comments) throws IOException {
      customStore0(new BufferedWriter(new OutputStreamWriter(out, "8859_1")),
                   comments, true);
  }
  //Override to stop '/' or ':' chars from being replaced by not called 
  //saveConvert(key, true, escUnicode)
  private void customStore0(BufferedWriter bw, String comments, boolean escUnicode)
          throws IOException {
      bw.write("#" + new Date().toString());
      bw.newLine();
      synchronized (this) {
          for (Enumeration e = keys(); e.hasMoreElements();) {
              String key = (String) e.nextElement();
              String val = (String) get(key);
              // Commented out to stop '/' or ':' chars being replaced
              //key = saveConvert(key, true, escUnicode);
              //val = saveConvert(val, false, escUnicode);
              bw.write(key + "=" + val);
              bw.newLine();
          }
      }
      bw.flush();
  }
}

Put the properties into the Properties object and save it using a store(...) method. The method will perform any escaping required. The Java documentation says:

"... For the key, all space characters are written with a preceding \ character. For the element, leading space characters, but not embedded or trailing space characters, are written with a preceding \ character. The key and element characters #, !, =, and : are written with a preceding backslash to ensure that they are properly loaded."

You only need to manually escape characters if you are creating / writing the file by hand.

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Conversely, if you want the file to contain unescaped colon characters, you are out of luck. Such a file is malformed and probably won't load properly using the Properties.load(...) methods. If you go down this route, you'll need to implement your own custom load and/or store methods.