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Share the post "Replacing strings with Java and Javascript"

Java and Javascript have different ways to replace strings like the feature “find and replace” that you see in text editors.

Java’s replace method is not ideal for noobs but only for people who know about regex. I am not that quite familiar with regex and if you wish to use that replace method under the String class in Java, you’d have to familiarize yourself with it in order to use it. The String class though, has lots of other useful methods that can be used to simulate how a search and replace function works. Here is a workaround method for people who only want a simple search and replace with the search and target both String. No regex knowledge needed.

The replace function contains two options. ‘i’ means the search would be case insensitive and ‘g’ means global, meaning it will search all instances of the search string within the str variable. If you do not include ‘g’ as its option, then only the first instance of the search string will be replaced.

Java and Javascript should have provided simple replace methods that greatly help newbies to these languages. The replaceString() method in Java is a good workaround for easy to use search and replace purposes in java.

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Share the post "Java: Database connection pooling in Apache Tomcat"

Database connection pooling is not a new concept. Typically, one would want to apply this concept into their application when dealing with database connections. The old style of creating database connections from scratch, maintaining them and closing them upon finishing the request is a very expensive process and takes a heavy load on the server itself.

Apache Tomcat supports connection pooling. One advantage of pooling is that it reduces the garbage collection load. Using connections objects that are in the pool, we do not need to worry about memory leaks of sort.

Once we request a connection and close it, the connection object will be sent back to the pool and wait for other requests. Hence, we are actually going to use existing connection objects. If the pool has ran out of connection objects, it will create a new one and adds it up to the total number of connections inside the pool.

To enable connection pooling in java, you only need to add this tag in the context.xml in the conf/ folder of apache tomcat’s working folder.

<Resource name="jdbc/dbname"
auth="Container"
type="javax.sql.DataSource"
factory="org.apache.tomcat.dbcp.dbcp.BasicDataSourceFactory"
username="micmic"
password="micmic"
driverClassName="com.mysql.jdbc.Driver"
url="jdbc:mysql://localhost:3306/dbname"
maxWait="1000"
removeAbandoned="true"
maxActive="30"
maxIdle="10"
removeAbandonedTimeout="60"
logAbandoned="true"/>

This tag must be inside the <context> tag.

To use this connection, you can have a method that looks similar to this

public static Connection getConnection() throws Exception {
Context initContext = new InitialContext();
Context envContext = (Context)initContext.lookup("java:/comp/env");
DataSource ds = (DataSource)envContext.lookup("jdbc/dbname");
ds.getConnection();
}

And use that same method to get a connection object from the pool:

Connection con = getConnection();

When you close this connection object after use, it will not close the object and garbage collect. Rather, it puts it back in the pool for the next use.

Please note that this sample code uses the MySQL Database. If you use other databases, check the appropriate driver class for the JDBC driver and make sure that you include the JDBC driver library in Apache Tomcat’s lib/ folder.

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Share the post "Java: How to parse HTML Pages"

There are many tools and/or libraries to use if you want to parse html pages. In java, one of the popular ones is called HTML Parser, which is what i use. It is not an application but a java library that you can plug into your classpath when compiling and executing your application using it. Go over to their site http://htmlparser.sourceforge.net/ and download it. When you extract the archive file, it contains the JAR file library , samples and documentation.

I mainly use HTML Parser for extraction purposes. However, you can also use it for transformation. Some cool features include having filters which help immensely in getting the html tags that you only need.

Here is a sample code that uses the HasAttributeFilter class to filter out only tags that contain this attribute. I use the FilterBean class in this example to access the site page’s content. You can also use the Parser class to do the same thing. Using either is up to your preference.

try {
  NodeFilter[] nff = {new HasAttributeFilter("id", "spoof")};
  FilterBean fb = new FilterBean();
  fb.setFilters (nff);
  fb.setURL(link);
  NodeList pageNodeList = fb.getNodes();
  System.out.println(pageNodeList.toHtml());
} catch (Exception e) { }

Suppose our link page contains the following html contents:

<body>
<p id="spoof">This is a sample paragraph</p>
<p id="officeid">Office id is 000123</p>
</body>

Once you execute that code, the output for System.out would be:

<p id="spoof">This is a sample paragraph</p>

the NodeList class is patterned after the Vector class and can be broken into separate tags. You just need to loop them. The documentation API contains all the classes of HTML Parser that you can use in your parsing needs. Take another filter as example, the TagNameFilter. if you replace HasAttributeFilter in the code with this

new TagNameFilter("p")

System.out will output as one string:
<p id="spoof">This is a sample paragraph</p>
<p id="officeid">Office id is 000123</p>

if you need to acecss each <p> tag separately you need to loop the pageNodeList object like this:

for (int i=0; i<pageNodeList.size(); i++) {
  System.out.println(((Node) pageNodeList.elementAt(i)).toHtml());
}

There you have it. HTML Parsing is so easy when using this helper library. It saves you the time and trouble of creating your own parser. Feel free to comment out if you have questions and/or problems.

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