Here is the one liner that appends the string with a prefix if the string doesn’t have a prefix
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String newString = oldString.startsWith("someprefix") ? oldString : "someprefix" + oldString; |
Author: T Tak
Hey ! I'm Tak. I'm a software developer since 2008 and been programming since I was 17 years, started with pascal. I love programming, teaching and building stuff on web.
Jsoup Maven and gradle dependecies
jsoup is a Java library for working with real-world HTML. It provides a very convenient API for extracting and manipulating data, using the best of DOM, CSS, and jquery-like methods. Maven If you use Maven to manage the dependencies in your Java project, you do not need to download; just place the following into your […]
ArrayList in java , add() method
Here is a real world example of using java.util.ArrayList add method.
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/* Soot - a J*va Optimization Framework * Copyright (C) 2003 Jennifer Lhotak * * This library is free software; you can redistribute it and/or * modify it under the terms of the GNU Lesser General Public * License as published by the Free Software Foundation; either * version 2.1 of the License, or (at your option) any later version. * * This library is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU * Lesser General Public License for more details. * * You should have received a copy of the GNU Lesser General Public * License along with this library; if not, write to the * Free Software Foundation, Inc., 59 Temple Place - Suite 330, * Boston, MA 02111-1307, USA. */ import java.util.ArrayList; import java.util.Iterator; import org.eclipse.jface.action.*; /** * Launches Soot with -f J for all classes in output dir of * selected project */ public class SootJimpleJavaProjectLauncher extends SootProjectLauncher { public void run(IAction action) { super.run(action); setCmd(); runSootDirectly(); runFinish(); } private void setCmd() { ArrayList commands = new ArrayList(); commands.add("--"+LaunchCommands.SOOT_CLASSPATH); Iterator it = getJavaProcessPath().iterator(); String cp = (String)it.next(); while (it.hasNext()){ cp = cp + getSootClasspath().getSeparator() + (String)it.next(); } cp = cp + getSootClasspath().getSeparator() + getClasspathAppend(); commands.add(cp); commands.add("--"+LaunchCommands.OUTPUT_DIR); commands.add(getOutputLocation()); getSootCommandList().addSingleOpt("--"+LaunchCommands.KEEP_LINE_NUMBER); getSootCommandList().addSingleOpt("--"+LaunchCommands.XML_ATTRIBUTES); Iterator it2 = getJavaProcessPath().iterator(); while (it2.hasNext()){ commands.add("--"+LaunchCommands.PROCESS_PATH); commands.add((String)it2.next()); } getSootCommandList().addDoubleOpt("--"+LaunchCommands.OUTPUT, LaunchCommands.JIMPLE_OUT); getSootCommandList().addDoubleOpt("--"+LaunchCommands.SRC_PREC,"java"); getSootCommandList().addSingleOpt(commands); } } |
Sort a list in java
Here is a nice example of sorting of a list
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package com.javagist.sort; import java.util.ArrayList; import java.util.Arrays; import java.util.Collections; import java.util.List; /** * This program sorts a list of Strings in ascending and descending order. * * @author javagist * */ public class SortExample { private List<String> namesList = Arrays.asList("Kevin", "Brian" , "Steve", "Bill", "Obama"); public static void main(String[] args) { SortExample sortExample = new SortExample(); System.out.println("Before sorting:" + sortExample.namesList); sortExample.sortList(sortExample.namesList); System.out.println("List in ascending order:" + sortExample.namesList); sortExample.reverseSortList(sortExample.namesList); System.out.println("List in descending orde :" + sortExample.namesList); // sort a new list and don't modify the order of original list List<String> keepOriginalOrderList = Arrays.asList("Kevin", "Brian" , "Steve", "Bill", "Obama"); List<String> sortedList = sortExample.sortListWithoutModifyingOriginalList(keepOriginalOrderList); System.out.println("List has preserved order :" + keepOriginalOrderList); System.out.println("New sorted list :" + sortedList); } /** * This method makes it obvious that any object that extends comparable can be sorted. * @param list - list to be sorted */ private <E extends Comparable<E>> void sortList(List<E> list){ Collections.sort(list); } /** * This method makes it obvious that any object that extends comparable can be sorted. * @param list - list to be reverse sorted */ private <E extends Comparable<E>> void reverseSortList(List<E> list){ Collections.sort(list, Collections.reverseOrder()); } /** * This method preserves the original List ordering. And returns a new sorted list * @param list - list to be sorted but not modified */ private <E extends Comparable<E>> List<E> sortListWithoutModifyingOriginalList(List<E> list){ List<E> newList = new ArrayList<E>(list); Collections.sort(newList); return newList; } } |
References http://programtalk.com/java/sort-list-java/
How to forwarding X11 connections from a remote host using sshj in java
This example demonstrates how forwarding X11 connections from a remote host can be accomplished.
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import net.schmizz.sshj.SSHClient; import net.schmizz.sshj.common.StreamCopier; import net.schmizz.sshj.connection.channel.direct.Session; import net.schmizz.sshj.connection.channel.direct.Session.Command; import net.schmizz.sshj.connection.channel.forwarded.SocketForwardingConnectListener; import java.io.IOException; import java.net.InetSocketAddress; public class X11 { public static void main(String... args) throws IOException, InterruptedException { final SSHClient ssh = new SSHClient(); // Compression makes X11 more feasible over slower connections // ssh.useCompression(); ssh.loadKnownHosts(); // NOTE: Forwarding incoming X connections to localhost:6000 only works if X is started without the // "-nolisten tcp" option (this is usually not the default for good reason) ssh.registerX11Forwarder(new SocketForwardingConnectListener(new InetSocketAddress("localhost", 6000))); ssh.connect("localhost"); try { ssh.authPublickey(System.getProperty("user.name")); Session sess = ssh.startSession(); // It is recommendable to send a fake cookie, and in your ConnectListener when a connection comes in replace // it with the real one. But here simply one from `xauth list` is being used. sess.reqX11Forwarding("MIT-MAGIC-COOKIE-1", "b0956167c9ad8f34c8a2788878307dc9", 0); final Command cmd = sess.exec("/usr/X11/bin/xcalc"); new StreamCopier(cmd.getInputStream(), System.out).spawn("stdout"); new StreamCopier(cmd.getErrorStream(), System.err).spawn("stderr"); // Wait for session & X11 channel to get closed ssh.getConnection().join(); } finally { ssh.disconnect(); } } } |
Retrofit Crawler
A simple web crawler that uses a Retrofit service to turn URLs into webpages.
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/* * Copyright (C) 2016 Square, Inc. * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package com.example.retrofit; import java.io.IOException; import java.lang.annotation.Annotation; import java.lang.reflect.Type; import java.util.ArrayList; import java.util.Collections; import java.util.LinkedHashSet; import java.util.List; import java.util.Set; import java.util.concurrent.ConcurrentHashMap; import java.util.concurrent.Executors; import java.util.concurrent.TimeUnit; import java.util.concurrent.atomic.AtomicInteger; import okhttp3.ConnectionPool; import okhttp3.Dispatcher; import okhttp3.HttpUrl; import okhttp3.OkHttpClient; import okhttp3.ResponseBody; import org.jsoup.Jsoup; import org.jsoup.nodes.Document; import org.jsoup.nodes.Element; import retrofit2.Call; import retrofit2.Callback; import retrofit2.Converter; import retrofit2.Response; import retrofit2.Retrofit; import retrofit2.http.GET; import retrofit2.http.Url; public final class Crawler { private final Set fetchedUrls = Collections.synchronizedSet( new LinkedHashSet()); private final ConcurrentHashMap hostnames = new ConcurrentHashMap<>(); private final PageService pageService; public Crawler(PageService pageService) { this.pageService = pageService; } public void crawlPage(HttpUrl url) { // Skip hosts that we've visited many times. AtomicInteger hostnameCount = new AtomicInteger(); AtomicInteger previous = hostnames.putIfAbsent(url.host(), hostnameCount); if (previous != null) hostnameCount = previous; if (hostnameCount.incrementAndGet() > 100) return; // Asynchronously visit URL. pageService.get(url).enqueue(new Callback() { @Override public void onResponse(Call call, Response response) { if (!response.isSuccessful()) { System.out.println(call.request().url() + ": failed: " + response.code()); return; } // Print this page's URL and title. Page page = response.body(); HttpUrl base = response.raw().request().url(); System.out.println(base + ": " + page.title); // Enqueue its links for visiting. for (String link : page.links) { HttpUrl linkUrl = base.resolve(link); if (linkUrl != null && !fetchedUrls.add(linkUrl)) { crawlPage(linkUrl); } } } @Override public void onFailure(Call call, Throwable t) { System.out.println(call.request().url() + ": failed: " + t); } }); } public static void main(String... args) throws Exception { Dispatcher dispatcher = new Dispatcher(Executors.newFixedThreadPool(20)); dispatcher.setMaxRequests(20); dispatcher.setMaxRequestsPerHost(1); OkHttpClient okHttpClient = new OkHttpClient.Builder() .dispatcher(dispatcher) .connectionPool(new ConnectionPool(100, 30, TimeUnit.SECONDS)) .build(); Retrofit retrofit = new Retrofit.Builder() .baseUrl(HttpUrl.parse("https://example.com/")) .addConverterFactory(PageAdapter.FACTORY) .client(okHttpClient) .build(); PageService pageService = retrofit.create(PageService.class); Crawler crawler = new Crawler(pageService); crawler.crawlPage(HttpUrl.parse(args[0])); } interface PageService { @GET Call get(@Url HttpUrl url); } static class Page { public final String title; public final List links; public Page(String title, List links) { this.title = title; this.links = links; } } static final class PageAdapter implements Converter { static final Converter.Factory FACTORY = new Converter.Factory() { @Override public Converter responseBodyConverter( Type type, Annotation[] annotations, Retrofit retrofit) { if (type == Page.class) return new PageAdapter(); return null; } }; @Override public Page convert(ResponseBody responseBody) throws IOException { Document document = Jsoup.parse(responseBody.string()); List links = new ArrayList<>(); for (Element element : document.select("a[href]")) { links.add(element.attr("href")); } return new Page(document.title(), Collections.unmodifiableList(links)); } } } |
Convert byte to Hexadecimal String and vice versa
Convert byte to Hexadecimal
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public static String bytesToHex(byte[] bytes) { final char[] hexArray = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F' }; char[] hexChars = new char[bytes.length * 2]; int v; for (int j = 0; j < bytes.length; j++) { v = bytes[j] & 0xFF; hexChars[j * 2] = hexArray[v >>> 4]; hexChars[j * 2 + 1] = hexArray[v & 0x0F]; } return new String(hexChars); } |
Convert Hexadecimal to byte
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public static byte[] hexToBytes(String s) { int len = s.length(); byte[] data = new byte[len / 2]; for (int i = 0; i < len; i += 2) { data[i / 2] = (byte) ((Character.digit(s.charAt(i), 16) << 4) + Character.digit(s.charAt(i + 1), 16)); } return data; } |
How to download and Upload a file through SFTP using java.
Here is a code example that shows how to download and upload a file through SFTP in java Download File
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import com.jcraft.jsch.Channel; import com.jcraft.jsch.ChannelSftp; import com.jcraft.jsch.JSch; import com.jcraft.jsch.JSchException; import com.jcraft.jsch.Session; import com.jcraft.jsch.SftpException; /** * * @author javagists.com * */ public class DownloadFileSFTP { public static void main(String[] args) throws Exception { JSch jsch = new JSch(); Session session = null; try { session = jsch.getSession("admin", "127.0.0.1", 22); session.setConfig("StrictHostKeyChecking", "no"); session.setPassword("pass"); session.connect(); Channel channel = session.openChannel("sftp"); channel.connect(); ChannelSftp sftpChannel = (ChannelSftp) channel; sftpChannel.get("/tmpremote/testDownload.txt", "/tmplocal/testDownload.txt"); sftpChannel.exit(); session.disconnect(); } catch (JSchException e) { e.printStackTrace(); } catch (SftpException e) { e.printStackTrace(); } } } |
Upload File
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import com.jcraft.jsch.Channel; import com.jcraft.jsch.ChannelSftp; import com.jcraft.jsch.JSch; import com.jcraft.jsch.JSchException; import com.jcraft.jsch.Session; import com.jcraft.jsch.SftpException; /** * * @author javagists.com * */ public class UploadFileSFTP { public static void main(String[] args) throws Exception { JSch jsch = new JSch(); Session session = null; try { session = jsch.getSession("admin", "127.0.0.1", 22); session.setConfig("StrictHostKeyChecking", "no"); session.setPassword("pass"); session.connect(); Channel channel = session.openChannel("sftp"); channel.connect(); ChannelSftp sftpChannel = (ChannelSftp) channel; sftpChannel.put("/tmplocal/testUpload.txt", "/tmpremote/testUpload.txt"); sftpChannel.exit(); session.disconnect(); } catch (JSchException e) { e.printStackTrace(); } catch (SftpException e) { e.printStackTrace(); } } } |
