How do I store properties as XML file?

By Wayan in Core API, IO 0 Comment

In the previous example, How do I load properties from XML file? we read properties from XML file. Now it’s the turn on how to store the properties as XML file.

package org.kodejava.io;

import java.io.FileOutputStream;
import java.nio.charset.StandardCharsets;
import java.util.Properties;

public class PropertiesToXml {
    public static void main(String[] args) throws Exception {
        Properties properties = new Properties();
        properties.setProperty("db.type", "mysql");
        properties.setProperty("db.url", "jdbc:mysql://localhost:3306/kodejava");
        properties.setProperty("db.username", "root");
        properties.setProperty("db.password", "");

        FileOutputStream fos = new FileOutputStream("db-config.xml");
        properties.storeToXML(fos, "Database Configuration", StandardCharsets.UTF_8);
    }
}

The saved XML file will look like the properties file below:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE properties SYSTEM "http://java.sun.com/dtd/properties.dtd">
<properties>
    <comment>Database Configuration</comment>
    <entry key="db.type">mysql</entry>
    <entry key="db.password"></entry>
    <entry key="db.username">root</entry>
    <entry key="db.url">jdbc:mysql://localhost:3306/kodejava</entry>
</properties>

How do I convert InputStream to String?

By Wayan in Core API, IO 1 Comment

This example will show you how to convert an InputStream into String. In the code snippet below we read a data.txt file, could be from common directory or from inside a jar file.

package org.kodejava.io;

import java.io.*;
import java.nio.charset.StandardCharsets;

public class StreamToString {

    public static void main(String[] args) throws Exception {
        StreamToString demo = new StreamToString();

        // Get input stream of our data file. This file can be in
        // the root of your application folder or inside a jar file
        // if the program is packed as a jar.
        InputStream is = demo.getClass().getResourceAsStream("/student.csv");

        // Call the method to convert the stream to string
        System.out.println(demo.convertStreamToString(is));
    }

    private String convertStreamToString(InputStream stream) throws IOException {
        // To convert the InputStream to String we use the
        // Reader.read(char[] buffer) method. We iterate until the
        // Reader return -1 which means there's no more data to
        // read. We use the StringWriter class to produce the string.
        if (stream != null) {
            Writer writer = new StringWriter();

            char[] buffer = new char[1024];
            try (stream) {
                Reader reader = new BufferedReader(new InputStreamReader(stream,
                        StandardCharsets.UTF_8));
                int length;
                while ((length = reader.read(buffer)) != -1) {
                    writer.write(buffer, 0, length);
                }
            }
            return writer.toString();
        }
        return "";
    }
}

How do I convert string into InputStream?

By Wayan in Core API, IO 0 Comment

Here you will find how to convert string into java.io.InputStream object using java.io.ByteArrayInputStream class.

package org.kodejava.io;

import java.io.*;
import java.nio.charset.StandardCharsets;

public class StringToStream {
    public static void main(String[] args) {
        String text = "Converting String to InputStream Example";

        // Convert String to InputStream using ByteArrayInputStream
        // class. This class constructor takes the string byte array
        // which can be done by calling the getBytes() method.
        InputStream stream = new ByteArrayInputStream(text.getBytes(StandardCharsets.UTF_8));
    }
}

How do I get an exception stack trace message?

By Wayan in Core API, IO 0 Comment

In this example we use the java.io.StringWriter and java.io.PrintWriter class to convert stack trace exception message to a string.

package org.kodejava.io;

import java.io.StringWriter;
import java.io.PrintWriter;

public class StackTraceToString {
    public static void main(String[] args) {
        try {
            int result = 10 / 0;
        } catch (Exception e) {
            // Create a StringWriter and a PrintWriter both of these object
            // will be used to convert the data in the stack trace to a string.
            StringWriter stringWriter = new StringWriter();
            PrintWriter printWriter = new PrintWriter(stringWriter);

            // Instead of writing the stack trace in the console we write it
            // to the PrintWriter, to get the stack trace message we then call
            // the toString() method of StringWriter.
            e.printStackTrace(printWriter);

            System.out.println("Error = " + stringWriter);
        }
    }
}

This code snippet print the following output:

Error = java.lang.ArithmeticException: / by zero
    at org.kodejava.io.StackTraceToString.main(StackTraceToString.java:9)

How do I use Console class to read user input?

By Wayan in Core API, IO 0 Comment

In the previous example, How do I read user input from console using Scanner class?, we use the java.util.Scanner class to read user input. In this example we use another new class introduced in the Java 1.6, the java.io.Console class.

The Console class provide methods like readLine() and readPassword(). The readPassword() method can be used to read user’s password. Using this method the user’s input will not be shown in the console. The password will be returned as an array of char.

package org.kodejava.io;

import java.io.Console;

public class ConsoleDemo {

    public static void main(String[] args) {
        // Get a console object, console can be null if not available.
        Console console = System.console();

        if (console == null) {
            System.out.println("Console is not available.");
            System.exit(1);
        }

        // Read username from the console
        String username = console.readLine("Username: ");

        // Read password, the password will not be echoed to the
        // console screen and returned as an array of characters.
        char[] password = console.readPassword("Password: ");

        if (username.equals("admin") && String.valueOf(password).equals("secret")) {
            console.printf("Welcome to Java Application %1$s.%n", username);
        } else {
            console.printf("Invalid username or password.%n");
        }
    }
}

The result of the code snippet above is:

Username: admin
Password:
Welcome to Java Application admin.