Java 从URL输入流
如何从URL获取InputStream 例如，我想获取urlJava 从URL输入流,java,url,inputstream,Java,Url,Inputstream,如何从URL获取InputStream 例如，我想获取urlwwwww.somewebsite.com/a.txt上的文件，并通过servlet将其作为Java中的InputStream读取 我试过了 InputStream is = new FileInputStream("wwww.somewebsite.com/a.txt"); 但我得到的是一个错误： java.io.FileNotFoundException 使用合适的URL（包括协议！）。例如 另见： 试试： final In
wwwww.somewebsite.com/a.txtInputStream is = new FileInputStream("wwww.somewebsite.com/a.txt");
java.io.FileNotFoundException
final InputStream is = new URL("http://wwww.somewebsite.com/a.txt").openStream();
www.somewebsite.com/a.txthttp://FileInputStream（c） 从任何URL获取输入流的方法是通过
URL.openStream（），URL.getConnection（）.getInputStream（），URLConnectionURL对象是解决此问题的通用方法。您可以使用URL访问本地文件，也可以访问网络承载的资源。URL类除了支持http://或https://之外，还支持file://协议，因此您可以继续使用。下面是一个完整的示例，它读取给定网页的内容。 该网页是从HTML表单读取的。我们使用标准的
InputStream<dependency>
<groupId>javax.servlet</groupId>
<artifactId>javax.servlet-api</artifactId>
<version>3.1.0</version>
<scope>provided</scope>
</dependency>
<dependency>
<groupId>commons-validator</groupId>
<artifactId>commons-validator</artifactId>
<version>1.6</version>
</dependency>
ReadWebPagewebagereaderpackage com.zetcode.service;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.URL;
import java.nio.charset.StandardCharsets;
import java.util.logging.Level;
import java.util.logging.Logger;
import java.util.stream.Collectors;
import org.apache.commons.validator.routines.UrlValidator;
public class WebPageReader {
private String webpage;
private String content;
public WebPageReader setWebPageName(String name) {
webpage = name;
return this;
}
public String getWebPageContent() {
try {
boolean valid = validateUrl(webpage);
if (!valid) {
content = "Invalid URL; use http(s)://www.example.com format";
return content;
}
URL url = new URL(webpage);
try (InputStream is = url.openStream();
BufferedReader br = new BufferedReader(
new InputStreamReader(is, StandardCharsets.UTF_8))) {
content = br.lines().collect(
Collectors.joining(System.lineSeparator()));
}
} catch (IOException ex) {
content = String.format("Cannot read webpage %s", ex);
Logger.getLogger(WebPageReader.class.getName()).log(Level.SEVERE, null, ex);
}
return content;
}
private boolean validateUrl(String webpage) {
UrlValidator urlValidator = new UrlValidator();
return urlValidator.isValid(webpage);
}
}
webagereader<!DOCTYPE html>
<html>
<head>
<title>Home page</title>
<meta charset="UTF-8">
</head>
<body>
<form action="ReadWebPage">
<label for="page">Enter a web page name:</label>
<input type="text" id="page" name="webpage">
<button type="submit">Submit</button>
</form>
</body>
</html>
主页
输入网页名称：
提交
urlToInputStream(url,httpHeaders);
映射private InputStream urlToInputStream(URL url, Map<String, String> args) {
HttpURLConnection con = null;
InputStream inputStream = null;
try {
con = (HttpURLConnection) url.openConnection();
con.setConnectTimeout(15000);
con.setReadTimeout(15000);
if (args != null) {
for (Entry<String, String> e : args.entrySet()) {
con.setRequestProperty(e.getKey(), e.getValue());
}
}
con.connect();
int responseCode = con.getResponseCode();
/* By default the connection will follow redirects. The following
* block is only entered if the implementation of HttpURLConnection
* does not perform the redirect. The exact behavior depends to
* the actual implementation (e.g. sun.net).
* !!! Attention: This block allows the connection to
* switch protocols (e.g. HTTP to HTTPS), which is <b>not</b>
* default behavior. See: https://stackoverflow.com/questions/1884230
* for more info!!!
*/
if (responseCode < 400 && responseCode > 299) {
String redirectUrl = con.getHeaderField("Location");
try {
URL newUrl = new URL(redirectUrl);
return urlToInputStream(newUrl, args);
} catch (MalformedURLException e) {
URL newUrl = new URL(url.getProtocol() + "://" + url.getHost() + redirectUrl);
return urlToInputStream(newUrl, args);
}
}
/*!!!!!*/
inputStream = con.getInputStream();
return inputStream;
} catch (Exception e) {
throw new RuntimeException(e);
}
}
私有输入流urlToInputStream（URL、映射参数）{
HttpURLConnection con=null；
InputStream InputStream=null；
试一试{
con=（HttpURLConnection）url.openConnection（）；
con.设置连接超时（15000）；
con.setReadTimeout（15000）；
如果（args！=null）{
对于（条目e:args.entrySet（））{
con.setRequestProperty（e.getKey（），e.getValue（））；
}
}
con.connect（）；
int responseCode=con.getResponseCode（）；
/*默认情况下，连接将遵循重定向
*仅当HttpURLConnection的实现
*不执行重定向。具体行为取决于
*实际实现（例如sun.net）。
*！！！注意：此块允许连接到
*切换协议（例如HTTP到HTTPS），这不是
*默认行为。请参阅：https://stackoverflow.com/questions/1884230
*更多信息！！！
*/
如果（响应代码<400&&responseCode>299）{
字符串重定向URL=con.getHeaderField（“位置”）；
试一试{
URL newUrl=新URL（重定向URL）；
返回urlToInputStream（newUrl，args）；
}捕获（格式错误）{
URL newUrl=新URL（URL.getProtocol（）+“：/”+URL.getHost（）+重定向URL）；
返回urlToInputStream（newUrl，args）；
}
}
/*!!!!!*/
inputStream=con.getInputStream（）；
返回输入流；
}捕获（例外e）{
抛出新的运行时异常（e）；
}
}
private InputStream getInputStreamFromUrl(URL url, String user, String passwd) throws IOException {
String encoded = Base64.getEncoder().encodeToString((user + ":" + passwd).getBytes(StandardCharsets.UTF_8));
Map<String,String> httpHeaders=new Map<>();
httpHeaders.put("Accept", "application/json");
httpHeaders.put("User-Agent", "myApplication");
httpHeaders.put("Authorization", "Basic " + encoded);
return urlToInputStream(url,httpHeaders);
}
private InputStream getInputStreamFromUrl（URL URL、字符串用户、字符串密码）引发IOException{
String encoded=Base64.getEncoder（）.encodeToString（（用户+”：“+passwd）.getBytes（标准字符集.utf8））；
Map httpHeaders=new Map（）；
httpHeaders.put（“接受”、“应用程序/json”）；
httpHeaders.put（“用户代理”、“我的应用程序”）；
httpHeaders.put（“授权”、“基本”+编码）；
返回urlToInputStream（url，httpHeaders）；
}
servletjavax.servlet.main（）的普通Java类中执行此操作时，会遇到完全相同的问题HttpURLConnectionHttpURLConnectionprivate InputStream urlToInputStream(URL url, Map<String, String> args) {
HttpURLConnection con = null;
InputStream inputStream = null;
try {
con = (HttpURLConnection) url.openConnection();
con.setConnectTimeout(15000);
con.setReadTimeout(15000);
if (args != null) {
for (Entry<String, String> e : args.entrySet()) {
con.setRequestProperty(e.getKey(), e.getValue());
}
}
con.connect();
int responseCode = con.getResponseCode();
/* By default the connection will follow redirects. The following
* block is only entered if the implementation of HttpURLConnection
* does not perform the redirect. The exact behavior depends to
* the actual implementation (e.g. sun.net).
* !!! Attention: This block allows the connection to
* switch protocols (e.g. HTTP to HTTPS), which is <b>not</b>
* default behavior. See: https://stackoverflow.com/questions/1884230
* for more info!!!
*/
if (responseCode < 400 && responseCode > 299) {
String redirectUrl = con.getHeaderField("Location");
try {
URL newUrl = new URL(redirectUrl);
return urlToInputStream(newUrl, args);
} catch (MalformedURLException e) {
URL newUrl = new URL(url.getProtocol() + "://" + url.getHost() + redirectUrl);
return urlToInputStream(newUrl, args);
}
}
/*!!!!!*/
inputStream = con.getInputStream();
return inputStream;
} catch (Exception e) {
throw new RuntimeException(e);
}
}
private InputStream getInputStreamFromUrl(URL url, String user, String passwd) throws IOException {
String encoded = Base64.getEncoder().encodeToString((user + ":" + passwd).getBytes(StandardCharsets.UTF_8));
Map<String,String> httpHeaders=new Map<>();
httpHeaders.put("Accept", "application/json");
httpHeaders.put("User-Agent", "myApplication");
httpHeaders.put("Authorization", "Basic " + encoded);
return urlToInputStream(url,httpHeaders);
}