Apache httpclient未知主机问题

Question

I am using the following apache http client snippet, taken from the website:

https://gist.github.com/Cyclenerd/41c737ee4b6ee4c767947af790d09e2c

Here is the code making a simple get request:

public final static void main(String[] args) throws Exception {
    // Setup a Trust Strategy that allows all certificates.
    // !!! DO NOT USE THIS IN PRODUCTION !!!
    SSLContext sslcontext = SSLContexts.custom().loadTrustMaterial(null, new TrustStrategy() {
        @Override
        public boolean isTrusted(X509Certificate[] arg0, String arg1) throws CertificateException {
            return true;
        }
    }).build();

    // Allow TLSv1 protocol only
    SSLConnectionSocketFactory sslsf = new SSLConnectionSocketFactory(
            sslcontext,
            new String[] { "TLSv1" },
            null,
            SSLConnectionSocketFactory.getDefaultHostnameVerifier());
    CloseableHttpClient httpclient = HttpClients.custom()
            .setSSLSocketFactory(sslsf)
            .build();
    try {
        // Get URL
        HttpGet httpget = new HttpGet("https://www.google.de");

        System.out.println("Executing request " + httpget.getRequestLine());
        CloseableHttpResponse response = httpclient.execute(httpget);
        try {
            HttpEntity entity = response.getEntity();
            System.out.println("----------------------------------------");
            System.out.println(response.getStatusLine());
            System.out.println(EntityUtils.toString(entity));
        } finally {
            response.close();
        }
    } finally {
        httpclient.close();
    }
 }

I keep getting the following exception :

Executing request GET https://www.google.de HTTP/1.1 Exception in thread "main" java.net.UnknownHostException: www.google.de

Answer 1

import org.apache.http.HttpEntity;
import org.apache.http.client.methods.CloseableHttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.conn.ssl.SSLConnectionSocketFactory;
import org.apache.http.conn.ssl.TrustStrategy;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.ssl.SSLContexts;
import org.apache.http.util.EntityUtils;
import javax.net.ssl.SSLContext;
import java.security.cert.CertificateException;
import java.security.cert.X509Certificate;

public class StackOverFlowIssue {

    public final static void main(String[] args) throws Exception {
    // Setup a Trust Strategy that allows all certificates.
    // !!! DO NOT USE THIS IN PRODUCTION !!!
    SSLContext sslcontext = SSLContexts.custom().loadTrustMaterial(null, new TrustStrategy() {
        @Override
        public boolean isTrusted(X509Certificate[] arg0, String arg1) throws CertificateException {
            return true;
        }
    }).build();

    // Allow TLSv1 protocol only
    SSLConnectionSocketFactory sslsf = new SSLConnectionSocketFactory(
            sslcontext,
            new String[] { "TLSv1" },
            null,
            SSLConnectionSocketFactory.getDefaultHostnameVerifier());
    CloseableHttpClient httpclient = HttpClients.custom()
            .setSSLSocketFactory(sslsf)
            .build();
    try {
        // Get URL
        HttpGet httpget = new HttpGet("https://www.google.de");

        System.out.println("Executing request " + httpget.getRequestLine());
        CloseableHttpResponse response = httpclient.execute(httpget);
        try {
            HttpEntity entity = response.getEntity();
            System.out.println("----------------------------------------");
            System.out.println(response.getStatusLine());
            System.out.println(EntityUtils.toString(entity));
        } finally {
            response.close();
        }
    } finally {
        httpclient.close();
    }
    }
}

Pom dependency

<dependency>
  <groupId>org.apache.httpcomponents</groupId>
  <artifactId>httpclient</artifactId>
  <version>4.5.3</version>
</dependency>

Answer 2

The code works with the following imports:

import java.io.IOException;
import java.security.KeyManagementException;
import java.security.KeyStoreException;
import java.security.NoSuchAlgorithmException;
import java.security.cert.CertificateException;
import java.security.cert.X509Certificate;

import javax.net.ssl.SSLContext;

import org.apache.http.HttpEntity;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.methods.CloseableHttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.conn.ssl.SSLConnectionSocketFactory;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.ssl.SSLContexts;
import org.apache.http.ssl.TrustStrategy;
import org.apache.http.util.EntityUtils;

Minor version change of the library, pom.xml:

    <!-- https://mvnrepository.com/artifact/org.apache.httpcomponents/httpclient -->
    <dependency>
        <groupId>org.apache.httpcomponents</groupId>
        <artifactId>httpclient</artifactId>
        <version>4.5.9</version>
    </dependency>

Problably there are some problems related to incorrent imports.

Answer 3

This answer may be a bit of topic, but while apache Http client is very popular and tested library, it seems like a lot of code just to send a simple GET request. There is a very simple and by far less known Http client that may not handle some complex issues, but for simple stuff like this is definitely more friendly to use. Below is the code that sends a GET request to " https://www.google.de " link.

private static void testHttpClient() {
    HttpClient client = new HttpClient();
    client.setContentType("text/html; charset=utf-8");
    String content = null;
    try {
        content = client.sendHttpRequest("https://www.google.de", HttpMethod.GET);
    } catch (IOException e) {
        content = TextUtils.getStacktrace(e, false);
    }
    System.out.println(content);
}

If you are interested, the library is called MgntUtils (written by me) and you can get it as Maven artifacts or Git (including source code and javadoc). Here is Link to Javadoc and Here is a link to an article about the library Here is maven artifact:

<dependency>
  <groupId>com.github.michaelgantman</groupId>
  <artifactId>MgntUtils</artifactId>
  <version>1.5.0.7</version>
</dependency>