java 网络编程基础 InetAddress类；URLDecoder和URLEncoder；URL和URLConnection；多线程下载文件示例

public class UrlEncodeTest {
public static void main(String[] args) throws UnsupportedEncodingException {
String url = "https://www.baidu.com/狗逼/";
//转码
String encodeUrl = URLEncoder.encode(url,"utf-8");
System.out.println(encodeUrl); //https%3A%2F%2Fwww.baidu.com%2F%E7%8B%97%E9%80%BC%2F
//解码
String str = URLDecoder.decode(encodeUrl,"utf-8");
System.out.println(str);//https://www.baidu.com/狗逼/ }
}

• String getFile(): 获取该URL资源名。
• String getHost(): 获取URL的主机名
• String getPath(): 获取该URL的路径部分
• int getPort(): 获取URL的端口号。
• String getProtocol(): 获取该URL的协议名称
• String getQuery() 获取该 URL 宇符串部分。
• URLConnection openConnection(): 返回一个URLConnection它代表了与该URL 所引用的远对象的连接。
• InputStream openStream() 打开与此URL连接，并返回一个用于读取该URL资源的 InputStream

多线程下载文件示例：

知识点：

• URL类openConnection() 所引用的远对象的连接; 对象的getContentLength方法获取响应头文件字节长度

import java.io.IOException;
import java.io.InputStream;
import java.io.RandomAccessFile;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLConnection;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;/**
* @ClassName ThreadPoolMultiDownLoad
* @projectName: object1
* @author: Zhangmingda
* @description： 使用多线程线程池方式下载文件
* date: 2021/5/9.
*/
public class ThreadPoolMultiDownLoad {
/**
* 要下文件的url地址
*/
private String urlString;
/**
* 线程数
*/
private int threadNum;
/**
* 保存文件的目录
*/
private String saveDir;
/**
* 文件的大小
*/
private int fileSize;
/**
* 线程池
*/
private static ExecutorService threadPool = null; /**
* 下载类构造方法
* @param urlString 文件地址
* @param threadNum 线程数设置
* @param saveDir 本地文件保存目录
*/
public ThreadPoolMultiDownLoad(String urlString, int threadNum, String saveDir) {
this.urlString = urlString;
this.threadNum = threadNum;
this.saveDir = saveDir;
}
/**
* 创建线程池实例的方法,确保线程池为单例(多线程同时运行时使用同一个实例)
*/
private static ExecutorService getThreadPool(){
if (threadPool == null){
synchronized (ThreadPoolMultiDownLoad.class){
if (threadPool == null){
threadPool = Executors.newCachedThreadPool();
}
}
}
return threadPool;
}
/**
* 获取文件大小方法
*/
private int getFileSize(URL url) throws IOException {
return url.openConnection().getContentLength();
}
/**
* 并发用分块下载写入的类
*/
private class DownPart implements Runnable {
private int startByte;
private int threadDownSize;
private RandomAccessFile accessFile;
private URL url; /** 本线程运行所需担心
* @param startByte 下载起始字节
* @param threadDownSize 本线程下载字节量
* @param accessFile 本地写入文件
*/
public DownPart(int startByte, int threadDownSize, RandomAccessFile accessFile,URL url) {
this.startByte = startByte;
this.threadDownSize = threadDownSize;
this.accessFile = accessFile;
this.url = url;
}
//本线程运行方法
@Override
public void run() {
int readcount = 0;
InputStream inputStream = null;
//打开http输入流
try {
URLConnection conn = this.url.openConnection();
/**
* 设置每个请求字节范围
*/
conn.setRequestProperty("Range","bytes=" + startByte + "-" + (startByte + threadDownSize));
inputStream = conn.getInputStream();
// //跳过非本线程需要下载的字节
// inputStream.skip(startByte);
/**
* 将本线程需要下载的字节写到本地文件中
*/
byte[] buffer = new byte[10240];
int len = 0;
while (readcount < this.threadDownSize && (len = inputStream.read(buffer)) != -1 ){
accessFile.write(buffer,0,len);
readcount += len;
}
System.out.println(Thread.currentThread().getName() + "下载写入了" + readcount + "字节的数据" );
} catch (IOException e) {
e.printStackTrace();
}finally {
try {
if (inputStream != null){inputStream.close(); }
if (accessFile != null){accessFile.close();} } catch (IOException e) {
e.printStackTrace();
}
} }
}
/**
* 下载文件方法
*/
public void download() throws IOException {
/**
* URL构造
*/
URL url = new URL(this.urlString);
/**
* 文件大小获取
*/
this.fileSize = getFileSize(url);
/**
* 每个线程下载的文件大小:由于fileSize总大小除以线程数量后，得出的小数部分会省略，所以每个线程多下载一字节
*/
int threadDownSize = this.threadNum == 1 ? this.fileSize : (this.fileSize / this.threadNum + 1);
/**
* 获取文件名
*/
String[] strings = this.urlString.split("/");
String fileName = strings[strings.length-1];
/**
* 本地预创建文件并预置文件大小
*/
String saveFilePath = this.saveDir + "/" + fileName;
System.out.println(saveFilePath);
RandomAccessFile accessFile = new RandomAccessFile(saveFilePath,"rw");
accessFile.setLength(this.fileSize);
accessFile.close();
/**
* 循环启动线程，分块写入到文件
*/
url = new URL(urlString);
for (int i=0; i<this.threadNum; i++){
//文件起始写入的位置
int startByte = i * threadDownSize;
//打开文件将文件指针移到该线程应该覆盖写入本地文件字节位置
RandomAccessFile randomAccessFile = new RandomAccessFile(saveFilePath,"rw");
randomAccessFile.seek(startByte); getThreadPool().submit(new DownPart(startByte,threadDownSize,randomAccessFile,url));
}
getThreadPool().shutdown();
} /**
* @param args
*/
public static void main(String[] args) throws IOException {
String ks3utilUrl = "https://ks3-cn-beijing.ksyun.com/ks3-import/KS3-import-tool-2.1.4-dist.zip";
new ThreadPoolMultiDownLoad(ks3utilUrl,4,"网络编程/src").download();
}
}