Find and replace words/lines in a file

Question

I have a file (more specifically, a log4j configuration file) and I want to be able to read in the file and pick out certain lines in the code and replace them. For example, within the file there is a string of text that indicates the directory it is stored in, or the level of the logger. I want to be able to replace those string of text without reading in the file, writing it to another file, and deleting the original file. Is there a more efficient way of doing find and replace texts in a file using Java?

Here is an example of the text file I'm trying to work with:

log4j.rootLogger=DEBUG, A0  log4j.appender.A0=org.apache.log4j.RollingFileAppender log4j.appender.A0.File=C:/log.txt log4j.appender.A0.MaxFileSize=100KB log4j.appender.A0.MaxBackupIndex=1  log4j.appender.A0.layout=org.apache.log4j.RollingFileAppender log4j.appender.A0.layout.ConversionPattern=%-4r [%t] %-5p: %c %x - %m%n 

I want to be able to read the file and replace 'DEBUG' with another level or replace the file directory name 'C:/log.txt'. The log configuration file is also written in xml. An example of that is featured below.

<?xml version="1.0" encoding="UTF-8" standalone="no"?> <!DOCTYPE log4j:configuration SYSTEM "log4j.dtd"> <log4j:configuration>     <appender class="org.apache.log4j.RollingFileAppender" name="A0">         <param name="append" value="false"/>         <param name="File" value="C:/log/.txt"/>         <param name="MaxBackupIndex" value="1"/>         <param name="MaxFileSize" value="100KB"/>         <layout class="org.apache.log4j.PatternLayout">             <param name="ConversionPattern" value="%-4r [%t] %-5p: %c %x - %m%n"/>         </layout>     </appender>     <root>         <level value="DEBUG"/>         <appender-ref ref="A0"/>     </root> </log4j:configuration> 

I'm thinking it may be possible to use a hash map for this type of implementation?

Answer 1

Any decent text editor has a search&replace facility that supports regular expressions.

If however, you have reason to reinvent the wheel in Java, you can do:

Path path = Paths.get("test.txt"); Charset charset = StandardCharsets.UTF_8;  String content = new String(Files.readAllBytes(path), charset); content = content.replaceAll("foo", "bar"); Files.write(path, content.getBytes(charset)); 

This only works for Java 7 or newer. If you are stuck on an older Java, you can do:

String content = IOUtils.toString(new FileInputStream(myfile), myencoding); content = content.replaceAll(myPattern, myReplacement); IOUtils.write(content, new FileOutputStream(myfile), myencoding); 

In this case, you'll need to add error handling and close the streams after you are done with them.

IOUtils is documented at http://commons.apache.org/proper/commons-io/javadocs/api-release/org/apache/commons/io/IOUtils.html