Kode Java - Learn Java by Examples

How do I get a list of files from FTP server?

By Wayan in Apache Commons, Commons Net Last modified: October 17, 2023 1 Comment

This example demonstrates how to retrieve a list of files from FTP server. First we create an instance of org.apache.commons.net.ftp.FTPClient. Connect to the FTP server and login with your username and password.

The listFiles() method of the FTPClient return the list of filenames contained in the current working directory. null if the list could not be obtained. If there are no filenames in the directory, a zero-length array is returned.

package org.kodejava.commons.net;

import org.apache.commons.io.FileUtils;
import org.apache.commons.net.ftp.FTPClient;
import org.apache.commons.net.ftp.FTPFile;

import java.io.IOException;

public class FTPListDemo {
    public static void main(String[] args) {
        FTPClient client = new FTPClient();

        try {
            client.connect("ftp.example.com");
            client.login("demo", "password");

            if (client.isConnected()) {
                // Obtain a list of filenames in the current working
                // directory. When no file is found, an empty array will
                // be returned.
                String[] names = client.listNames();
                for (String name : names) {
                    System.out.println("Name = " + name);
                }

                FTPFile[] ftpFiles = client.listFiles();
                for (FTPFile ftpFile : ftpFiles) {
                    // Check if FTPFile is a regular file
                    if (ftpFile.getType() == FTPFile.FILE_TYPE) {
                        System.out.printf("FTPFile: %s; %s%n",
                            ftpFile.getName(),
                            FileUtils.byteCountToDisplaySize(ftpFile.getSize()));
                    }
                }
            }
            client.logout();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                client.disconnect();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

Here is the example result of our code:

Name = example.html
Name = Touch.dat
FTPFile: examples.html; 1 bytes
FTPFile: Touch.dat; 0 bytes

Maven Dependencies

<dependencies>
    <dependency>
        <groupId>commons-net</groupId>
        <artifactId>commons-net</artifactId>
        <version>3.10.0</version>
    </dependency>
    <dependency>
        <groupId>commons-io</groupId>
        <artifactId>commons-io</artifactId>
        <version>2.14.0</version>
    </dependency>
</dependencies>

How do I upload file to FTP server?

This example demonstrates how to upload file to FTP server.

package org.kodejava.commons.net;

import org.apache.commons.net.ftp.FTPClient;

import java.io.IOException;
import java.io.InputStream;

public class FTPUploadDemo {
    public static void main(String[] args) {
        FTPClient client = new FTPClient();
        String filename = "data.txt";

        // Read the file from the resources folder.
        ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
        try (InputStream is = classLoader.getResourceAsStream(filename)) {
            client.connect("ftp.example.com");
            boolean login = client.login("demo", "password");
            if (login) {
                System.out.println("Login success...");

                // Store file to server
                client.storeFile(filename, is);
                client.logout();
            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                client.disconnect();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

Maven Dependencies

<dependency>
    <groupId>commons-net</groupId>
    <artifactId>commons-net</artifactId>
    <version>3.10.0</version>
</dependency>

How do I download file from FTP server?

By Wayan in Apache Commons, Commons Net Last modified: October 17, 2023 19 Comments

This example demonstrates how to download a file from FTP server. To download a file, we first connect to the FTP server and then login by supplying the username and password. To download the file we call retrieveFile() method of the FTPClient object. This method takes two parameters, the remote filename and an OutputStream of the local file where the download to be saved.

package org.kodejava.commons.net;

import org.apache.commons.net.ftp.FTPClient;

import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStream;

public class FTPDownloadDemo {
    public static void main(String[] args) {
        // The local filename and remote filename to be downloaded.
        String filename = "data.txt";

        FTPClient client = new FTPClient();
        try (OutputStream os = new FileOutputStream(filename)) {
            client.connect("ftp.example.com");
            boolean login = client.login("demo", "password");
            if (login) {
                System.out.println("Login success...");

                // Download file from FTP server.
                boolean status = client.retrieveFile(filename, os);
                System.out.println("status = " + status);
                System.out.println("reply  = " + client.getReplyString());
            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                client.disconnect();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

If the download process was success, you will see the following output printed:

status = true
reply  = 226 Transfer complete.

Maven Dependencies

<dependency>
    <groupId>commons-net</groupId>
    <artifactId>commons-net</artifactId>
    <version>3.10.0</version>
</dependency>

How do I connect to FTP server?

By Wayan in Apache Commons, Commons Net Last modified: October 17, 2023 2 Comments

The File Transfer Protocol (FTP) is a standard network protocol used to transfer computer files between a client and server on a computer network. The example below shows you how to connect to an FTP server.

In this example we are using the FTPClient class of the Apache Commons Net library. To connect to the server, we need to provide the FTP server name. Login to the server can be done by calling the login() method of this class with a valid username and password. To logout we call the logout() method.

Let’s try the code snippet below:

package org.kodejava.commons.net;

import org.apache.commons.net.ftp.FTPClient;

import java.io.IOException;

public class FTPConnectDemo {
    public static void main(String[] args) {
        FTPClient client = new FTPClient();

        try {
            client.connect("ftp.example.com");

            // When login success, the login method returns true.
            boolean login = client.login("demo", "password");
            if (login) {
                System.out.println("Login success...");

                // When logout success, the logout method returns true.
                boolean logout = client.logout();
                if (logout) {
                    System.out.println("Logout from FTP server...");
                }
            } else {
                System.out.println("Login fail...");
            }

        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                // Closes the connection to the FTP server
                client.disconnect();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

Maven Dependencies

<dependency>
    <groupId>commons-net</groupId>
    <artifactId>commons-net</artifactId>
    <version>3.10.0</version>
</dependency>

How do I touch a file using Apache Commons IO?

By Wayan in Apache Commons, Commons IO Last modified: October 2, 2023 0 Comment

This example demonstrates a touch command just like Unix touch command. If the file to be touched doesn’t exist, a new empty file will be created.

package org.kodejava.commons.io;

import org.apache.commons.io.FileUtils;

import java.io.File;
import java.io.IOException;

public class TouchFileExample {
    public static void main(String[] args) {
        try {
            File file = new File("Touch.dat");

            // Touch the file. When the file does not exist, a new file will be
            // created. If the file exists, change the file timestamp.
            FileUtils.touch(file);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

Maven Dependencies

<dependency>
    <groupId>commons-io</groupId>
    <artifactId>commons-io</artifactId>
    <version>2.14.0</version>
</dependency>

How do I delete directory recursively?

By Wayan in Apache Commons, Commons IO Last modified: October 2, 2023 0 Comment

Using the FileUtils.deleteDirectory() from the Apache Commons IO library, we can simplify the process of deleting directory and everything below it recursively.

package org.kodejava.commons.io;

import org.apache.commons.io.FileUtils;

import java.io.File;
import java.io.IOException;

public class DeleteDirectory {
    public static void main(String[] args) {
        try {
            File directory = new File("F:/Temp");

            // Deletes a directory recursively. When a deletion process is failed, an
            // IOException will be thrown; that's why we catch the exception.
            FileUtils.deleteDirectory(directory);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

Maven Dependencies

<dependency>
    <groupId>commons-io</groupId>
    <artifactId>commons-io</artifactId>
    <version>2.14.0</version>
</dependency>

How do I create a human-readable file size?

By Wayan in Apache Commons, Commons IO Last modified: October 2, 2023 0 Comment

This example demonstrates how to create a human-readable file size using the FileUtils class of the Apache Commons IO library. The byteCountToDisplaySize() method take the file size in bytes and return a human-readable display of the file size in bytes, kilobytes, megabytes, gigabytes, etc.

package org.kodejava.commons.io;

import org.apache.commons.io.FileUtils;

import java.io.File;

public class ReadableFileSize {
    public static void main(String[] args) {
        File file = new File("D:/Downloads/jdk-17_windows-x64_bin.exe");

        long size = file.length();
        String display = FileUtils.byteCountToDisplaySize(size);

        System.out.println("Name    = " + file.getName());
        System.out.println("Size    = " + size);
        System.out.println("Display = " + display);
    }
}

Here are the results of our program:

Name    = jdk-17_windows-x64_bin.exe
Size    = 159373640
Display = 151 MB

Maven Dependencies

<dependency>
    <groupId>commons-io</groupId>
    <artifactId>commons-io</artifactId>
    <version>2.14.0</version>
</dependency>

How do I read an XML document using JDOM?

By Wayan in JDOM Last modified: May 18, 2023 0 Comment

This example provide a small code snippet on how to use JDOM to parse an XML document, iterates each of the element and read the element or attributes values. To play with this example you have to have the JDOM library. You can download it from JDOM website.

package org.kodejava.jdom;

import org.jdom2.Document;
import org.jdom2.Element;
import org.jdom2.input.SAXBuilder;

import java.io.ByteArrayInputStream;
import java.nio.charset.StandardCharsets;
import java.util.List;

public class ReadXmlDocument {
    public static void main(String[] args) {
        // Our imaginary xml file to be processed in this example.
        String data = """
                <root>
                    <row>
                        <column name="username" length="16">admin</column>
                        <column name="password" length="128">secret</column>
                    </row>
                    <row>
                        <column name="username" length="16">jdoe</column>
                        <column name="password" length="128">password</column>
                    </row>
                </root>""";

        // Create an instance of SAXBuilder
        SAXBuilder builder = new SAXBuilder();
        try {
            // Tell the SAXBuilder to build the Document object from the
            // InputStream supplied.
            Document document = builder.build(
                    new ByteArrayInputStream(data.getBytes(StandardCharsets.UTF_8)));

            // Get our xml document root element which equals to the
            // <root> tag in the xml document.
            Element root = document.getRootElement();

            // Get all the children named with <row> in the document.
            // The method return the children as a java.util.List
            // object.
            List<Element> rows = root.getChildren("row");
            for (Element row : rows) {
                // Convert each row to an Element object and get its
                // children which will return a collection of <column>
                // elements. When we have to column row we can read
                // the attribute value (name, length) as defined above
                // and also read its value (between the <column></column>
                // tag) by calling the getText() method.
                //
                // The getAttribute() method also provide a handy method
                // if we want to convert the attribute value to a correct
                // org.kodejava.data type, in the example we read the length attribute
                // value as an integer.
                List<Element> columns = row.getChildren("column");
                for (Element column : columns) {
                    String name = column.getAttribute("name").getValue();
                    String value = column.getText();
                    int length = column.getAttribute("length").getIntValue();

                    System.out.println("name = " + name);
                    System.out.println("value = " + value);
                    System.out.println("length = " + length);
                }
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

Maven Dependencies

<dependency>
    <groupId>org.jdom</groupId>
    <artifactId>jdom2</artifactId>
    <version>2.0.6.1</version>
</dependency>

How do I determine bean’s property type?

By Wayan in Apache Commons, Commons Beanutils Last modified: May 18, 2023 0 Comment

Using the PropertyUtils.getPropertyType() we can determine the bean property type. This method return a Class object of bean’s property type.

package org.kodejava.commons.beanutils;

import org.apache.commons.beanutils.PropertyUtils;
import org.kodejava.commons.beanutils.support.Record;

public class PropertyType {
    public static void main(String[] args) {
        Record record = new Record();
        record.setTitle("Magical Mystery Tour");

        try {
            /*
             * Using PropertyUtils.getPropertyType() to determine the type of
             * title property.
             */
            Class<?> type = PropertyUtils.getPropertyType(record, "title");
            System.out.println("type = " + type.getName());

            String value = (String) PropertyUtils.getProperty(record, "title");
            System.out.println("value = " + value);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

package org.kodejava.commons.beanutils.support;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class Record {
    private Long id;
    private String title;
    private List<Track> tracks = new ArrayList<>();
    private Map<String, Track> mapTracks = new HashMap<>();

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    public List<Track> getTracks() {
        return tracks;
    }

    public void setTracks(List<Track> tracks) {
        this.tracks = tracks;
    }

    public void setMapTracks(Map<String, Track> mapTracks) {
        this.mapTracks = mapTracks;
    }

    public Map<String, Track> getMapTracks() {
        return mapTracks;
    }
}

The output of the code snippet above:

type = java.lang.String
value = Magical Mystery Tour

Maven Dependencies

<dependency>
    <groupId>commons-beanutils</groupId>
    <artifactId>commons-beanutils</artifactId>
    <version>1.9.4</version>
</dependency>

How do I read mapped bean’s property value?

By Wayan in Apache Commons, Commons Beanutils Last modified: May 18, 2023 0 Comment

In this example you’ll see how to read mapped property value of a bean. We use PropertyUtils.getMappedProperty() method the read the mapped property of the Record object that consist of Track objects.

package org.kodejava.commons.beanutils;

import org.apache.commons.beanutils.PropertyUtils;
import org.kodejava.commons.beanutils.support.Track;
import org.kodejava.commons.beanutils.support.Record;

import java.util.HashMap;
import java.util.Map;

public class ReadMapProperty {
    public static void main(String[] args) {
        Record record = new Record();
        record.setTitle("Abbey Road");

        Track track1 = new Track();
        track1.setTitle("Come Together");

        Track track2 = new Track();
        track2.setTitle("Something");

        Map<String, Track> tracks = new HashMap<>();
        tracks.put("1", track1);
        tracks.put("2", track2);

        record.setMapTracks(tracks);

        try {
            Track track = (Track) PropertyUtils.getMappedProperty(record, "mapTracks(1)");
            System.out.println("track.getTitle() = " + track.getTitle());
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

package org.kodejava.commons.beanutils;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class Record {
    private Long id;
    private String title;
    private List<Track> tracks = new ArrayList<>();
    private Map<String, Track> mapTracks = new HashMap<>();

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    public List<Track> getTracks() {
        return tracks;
    }

    public void setTracks(List<Track> tracks) {
        this.tracks = tracks;
    }

    public void setMapTracks(Map<String, Track> mapTracks) {
        this.mapTracks = mapTracks;
    }

    public Map<String, Track> getMapTracks() {
        return mapTracks;
    }
}

And here is the result of our program.

track.getTitle() = Come Together

Maven Dependencies

<dependency>
    <groupId>commons-beanutils</groupId>
    <artifactId>commons-beanutils</artifactId>
    <version>1.9.4</version>
</dependency>