如何避免用StringBuilder或Java中的String占用内存

Question

I am getting a lot of data from a webservice containing xml entity references. While replacing those with the respective characters I am getting an out of memory error. Can anybody give an example of how to avoid that? I have been stuck for two days on this problem.

This is my code:

public  String decodeXMLData(String s)
 {
     s = s.replaceAll(">",">");
     System.out.println("string value is"+s);

     s = s.replaceAll("&lt;", "<"); 
     System.out.println("string value1 is"+s);
     s = s.replaceAll("&amp;", "&");

     s = s.replaceAll("&quot;", "\"");

      s = s.replaceAll("&apos;", "'");

      s = s.replaceAll("&nbsp;", " ");

     return s;
 } 

Answer 1

You should use a SAX parser, not parse it on your own.

Just look in to these resources, they have code samples too:

• http://www.mkyong.com/java/how-to-read-xml-file-in-java-sax-parser/
• http://www.java-samples.com/showtutorial.php?tutorialid=152
• http://www.totheriver.com/learn/xml/xmltutorial.html

Answer 2

Take a look at Apache Commons Lang | StringEscapeUtils.unescapeHtml .

Answer 3

Calling five times replaceAll, you are creating five new String objects. In total, you are working with six Strings. This is not an efficent way to XML-decode a string.

I reccommend you using a more robust implementation of XML-encoding/decoding methods, like those contained in Commons Lang libraries. In particular, StringEscapeUtils may help you to get your job done.

Answer 4

The method as shown would not be a source of out of memory errors (unless the string you are handling is as big as the remaining free heap).

What uou could be running into is the fact that String.substring() calls do not allocate a new string, but create a string object which re-uses the one that substring is called on. If your code exists of reading large buffers and creating strings from those buffers, you might need to use new String(str.substring(index)) to force reallocation of the string values into new small char arrays.

Answer 5

You can try increasing JVM memory, but that will only delay the inevitable if the problem is serious (ie if you're trying to claim gigabytes for example).

If you've got a single String that causes you to run out of memory trying to do this, it must be humongous :) Suggestion to use a SAX parser to handle it and print it in bits and pieces is a good one. Or split it up into smaller bits yourself and send each of those to a routine that does what you want and discard the result afterwards.