Programming Posts

[Java] Creating a Microsoft Word Report Easily using Servlet and A Plain HTML Template

Yesterday one of my friend, Edward Barchia, asked me a very simple question, “how can i creating an MSWord Report without using Jasper Report”. Because somehow, jasper report creates a very weird output when exported into Word file (.doc).

One fastest solution is using a html file, and renamed into .doc. Not an elegant solution, but perhaps (at that moment) is the best solution we had.

Okay, so basically what i need is only 2 files, 1 html template and a java servlet files. This is my HTML template, i put it on drie E and name it hello.html

<html>
	<head></head>
	<body>
		Test, hello ${name}
	</body>
</html>

And this is my servlet file,

package com.edw.testdownloaddoc.servlet;

import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.FileReader;
import java.io.IOException;
import java.io.OutputStream;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.apache.commons.io.IOUtils;

@WebServlet(name = "downloadServlet", urlPatterns = {"/downloadServlet"})
public class DownloadServlet extends HttpServlet {

    protected void processRequest(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        BufferedReader downloadFile = new BufferedReader(new FileReader("e:\\hello.html"));
        FileInputStream inputStream = null;
        OutputStream outStream = null;
        try {
            String s;
            StringBuilder sb = new StringBuilder();
            while ((s=downloadFile.readLine()) != null) {
                if(s.contains("${name}"))
                    s = s.replace("${name}", "Edwin");
                sb.append(s);
            }
 
            response.setContentLength((int) sb.toString().length());
            response.setContentType("application/msword");           
 
            // response header
            String nameFile = "hello.doc";
            String headerKey = "Content-Disposition";
            String headerValue = String.format("attachment; filename=\"%s\"",nameFile);
            response.setHeader(headerKey, headerValue);
 
            // Write response
            outStream = response.getOutputStream();
            IOUtils.write(sb.toString(), outStream);
        } catch (Exception e) {
            e.printStackTrace();
        } finally{
            IOUtils.closeQuietly(downloadFile);
            IOUtils.closeQuietly(inputStream);
            IOUtils.closeQuietly(outStream);
        }
    }

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        processRequest(request, response);
    }
}

Oh, and before i forgot, this is my pom.xml dependencies

<dependencies>
	<dependency>
		<groupId>commons-io</groupId>
		<artifactId>commons-io</artifactId>
		<version>2.2</version>
	</dependency>
	<dependency>
		<groupId>javax</groupId>
		<artifactId>javaee-web-api</artifactId>
		<version>7.0</version>
		<scope>provided</scope>
	</dependency>
</dependencies>

This is the final output looks like,
helloworld

How to Perform “Autopsy” on OutOfMemoryError Application

Just several days ago, my application was down because of OutOfMemoryError, and I haven’t got a clue what the root cause is. That’s why I’m looking for a way on how to find the culprit when my application is down again. So im using this jvm parameter to dump all the object on memory when OutOfMemoryError happen.

-XX:+HeapDumpOnOutOfMemoryError -XX:HeapDumpPath=E:\ -Xmx10m -Xms10m

For example, im using this java class to simulate OutOfMemoryError,

package mybatistesting;

import java.util.ArrayList;
import java.util.List;

public class MyBatisTesting {
    
    public static void main(String[] args) throws Exception {
        List list = new ArrayList();
        for (int i = 0; i < 10000000000l; i++) {
            list.add(i+""+i+""+i);
            if(i%1000==0)
                System.out.println("adding -- "+i);
        }
    }
}

As you can see on your console log,

java.lang.OutOfMemoryError: GC overhead limit exceeded
Dumping heap to E:\java_pid5812.hprof ...
Heap dump file created [15155736 bytes in 0.237 secs]

You can open java_pid5812.hprof using your preferable application, for example using Eclipse MAT or JProfiler.

eclipse mat

jprofiler 1

jprofiler 2

Have fun 😉

Weird MyBatis Error, “Error setting null for parameter [number] with JdbcType OTHER”

I had a very weird error today, when connecting MyBatis to Oracle Database, the complete error is like this,

Error setting null for parameter #2 with JdbcType OTHER . 
Try setting a different JdbcType for this parameter or a different jdbcTypeForNull configuration property. 
Cause: java.sql.SQLException: Invalid column type: 1111

After researching for a while, i found out that it happen because i miss to fill a parameter on mybatis xml query file. This is my xml file,

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd" >
<mapper namespace="mybatistesting.MyMapper" >    
    <select resultType="java.util.Map" id="select" parameterType="java.util.Map">
        SELECT
            *
        FROM
            RISALAH
        WHERE UUID = #{UUID} AND CONTENT = #{CONTENT}
    </select>
</mapper>

And this is my main java file,

package mybatistesting;

import java.util.HashMap;
import java.util.Map;
import mybatistesting.config.MyBatisSqlSessionFactory;
import org.apache.ibatis.session.SqlSession;

public class MyBatisTesting {

    public static void main(String[] args) throws Exception {
        SqlSession sqlSession = MyBatisSqlSessionFactory.getSqlSessionFactory().openSession(true);
        MyMapper mapper = sqlSession.getMapper(MyMapper.class);
        Map map1 = new HashMap();
        map1.put("UUID", "1");
        for (Map map : mapper.select(map1)) {
            System.out.println("map "+map);
        }
    }
}

As you can see, i only set UUID as query parameter on my java file, despite that i need at least 2 parameter on my xml file. Here is how to fix it,

package mybatistesting;

import java.util.HashMap;
import java.util.Map;
import mybatistesting.config.MyBatisSqlSessionFactory;
import org.apache.ibatis.session.SqlSession;

public class MyBatisTesting {

    public static void main(String[] args) throws Exception {
        SqlSession sqlSession = MyBatisSqlSessionFactory.getSqlSessionFactory().openSession(true);
        MyMapper mapper = sqlSession.getMapper(MyMapper.class);
        Map map1 = new HashMap();
        map1.put("UUID", "1");
        map1.put("CONTENT", "1");
        for (Map map : mapper.select(map1)) {
            System.out.println("map "+map);
        }
    }
}

Hope it helps others, cheers 😉

How to Simulate and Finding Connection Leak in Oracle

It’s been a while since the last time i’ve write tutorials in my blog, but i found a very interesting case that perhaps helped a lot of people. Today im trying to create a simple test case to simulate a connection leak and how to search for it.

First is creating a simple unclosed connection query using java,

package com.edw;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;

public class Main {

    public static void main(String[] args) throws Exception {
        System.out.println("starting --------");
        
        Class.forName("oracle.jdbc.driver.OracleDriver");
        Connection connection = DriverManager.getConnection("jdbc:oracle:thin:@localhost:1521:xe", "USERNAME", "password");
        Statement statement = connection.createStatement();
        ResultSet resultSet = statement.executeQuery("SELECT * FROM INVALID"); // example table name is INVALID
        
        while(resultSet.next()) {
            System.out.println(resultSet.getString(1));
            System.out.println(resultSet.getString(2));
            System.out.println(resultSet.getString(3));
            System.out.println("=============");
        }
        
        System.out.println("ending --------");
        
        while(true) {
            Thread.sleep(10000);
            System.out.println("testing --------");
        }
    
    }
}

It will create an unclosed query that will hanging on my oracle connection.
And next, is my oracle query to find the hanging queries,

select LAST_CALL_ET, SQL_TEXT, username, machine, to_char(logon_time, 'ddMon hh24:mi') as login, 
    SQL_HASH_VALUE, PREV_HASH_VALUE, status
from v$session, v$sql 
where username='USERNAME' and HASH_VALUE =  PREV_HASH_VALUE
order by last_call_et desc;

it will show result like this,

LAST_CALL_ET SQL_TEXT                USERNAME     MACHINE        LOGIN                SQL_HASH_VALUE PREV_HASH_VALUE STATUS 
------------ ---------------------- ------------- -------------- -------------------- -------------- --------------- --------
          91 SELECT * FROM INVALID   USERNAME     edw      	     03Mar 11:53                       0       621168917 INACTIVE 

As you can see the result on the first column, “SELECT * FROM INVALID” query has run for more than 90 seconds.
So i can easily find the java class culprit who run that query.

FYI, this is my Oracle version,

select * from v$version;

BANNER                                                                         
--------------------------------------------------------------------------------
Oracle Database 11g Express Edition Release 11.2.0.2.0 - Production              
PL/SQL Release 11.2.0.2.0 - Production                                           
CORE	11.2.0.2.0	Production                                                         
TNS for 32-bit Windows: Version 11.2.0.2.0 - Production                          
NLSRTL Version 11.2.0.2.0 - Production   

I Hope this tutorial can help others, have fun 🙂

[Weird Javascript Error] Leading Zero on Integer Variable Become Octal on Old Browser

Ive met a very weird error, that somehow never occurs to me on my browser. I found this error only happen on old mozilla browsers, and only happen on javascript’s parseInt method. Here is a simple example,

alert(parseInt("09")-1);

When im running it on my browser (Mozilla version 34), this is what happen,
mozillanew

But when running on old browsers (Mozilla version 3.6), this is what happen,
mozillaold

I finally found out that that on old browsers, leading zeros are treated as octal values instead of plain integers. So this is my workaround,

alert(parseInt("09".replace(/^[0]+/g,""))-1);

I removed the leading zero before parsing it into int.

Hope it can help others 🙂