How to ignore SSL certificate errors in Apache HttpClient 4.0

Apache HttpClient 4.5.5

HttpClient httpClient = HttpClients
            .custom()
            .setSSLContext(new SSLContextBuilder().loadTrustMaterial(null, TrustAllStrategy.INSTANCE).build())
            .setSSLHostnameVerifier(NoopHostnameVerifier.INSTANCE)
            .build();

No deprecated API has been used.

Simple verifiable test case:

package org.apache.http.client.test;

import org.apache.http.HttpResponse;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.client.methods.HttpUriRequest;
import org.apache.http.conn.ssl.NoopHostnameVerifier;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.ssl.SSLContextBuilder;
import org.junit.Before;
import org.junit.Test;

import java.io.IOException;
import java.security.KeyManagementException;
import java.security.KeyStoreException;
import java.security.NoSuchAlgorithmException;

public class ApacheHttpClientTest {

    private HttpClient httpClient;

    @Before
    public void initClient() throws NoSuchAlgorithmException, KeyManagementException, KeyStoreException {
        httpClient = HttpClients
                .custom()
                .setSSLContext(new SSLContextBuilder().loadTrustMaterial(null, TrustAllStrategy.INSTANCE).build())
                .setSSLHostnameVerifier(NoopHostnameVerifier.INSTANCE)
                .build();
    }

    @Test
    public void apacheHttpClient455Test() throws IOException {
        executeRequestAndVerifyStatusIsOk("https://expired.badssl.com");
        executeRequestAndVerifyStatusIsOk("https://wrong.host.badssl.com");
        executeRequestAndVerifyStatusIsOk("https://self-signed.badssl.com");
        executeRequestAndVerifyStatusIsOk("https://untrusted-root.badssl.com");
        executeRequestAndVerifyStatusIsOk("https://revoked.badssl.com");
        executeRequestAndVerifyStatusIsOk("https://pinning-test.badssl.com");
        executeRequestAndVerifyStatusIsOk("https://sha1-intermediate.badssl.com");
    }

    private void executeRequestAndVerifyStatusIsOk(String url) throws IOException {
        HttpUriRequest request = new HttpGet(url);

        HttpResponse response = httpClient.execute(request);
        int statusCode = response.getStatusLine().getStatusCode();

        assert statusCode == 200;
    }
}

You need to create a SSLContext with your own TrustManager and create HTTPS scheme using this context. Here is the code,

SSLContext sslContext = SSLContext.getInstance("SSL");

// set up a TrustManager that trusts everything
sslContext.init(null, new TrustManager[] { new X509TrustManager() {
            public X509Certificate[] getAcceptedIssuers() {
                    System.out.println("getAcceptedIssuers =============");
                    return null;
            }

            public void checkClientTrusted(X509Certificate[] certs,
                            String authType) {
                    System.out.println("checkClientTrusted =============");
            }

            public void checkServerTrusted(X509Certificate[] certs,
                            String authType) {
                    System.out.println("checkServerTrusted =============");
            }
} }, new SecureRandom());

SSLSocketFactory sf = new SSLSocketFactory(sslContext);
Scheme httpsScheme = new Scheme("https", 443, sf);
SchemeRegistry schemeRegistry = new SchemeRegistry();
schemeRegistry.register(httpsScheme);

// apache HttpClient version >4.2 should use BasicClientConnectionManager
ClientConnectionManager cm = new SingleClientConnManager(schemeRegistry);
HttpClient httpClient = new DefaultHttpClient(cm);

All of the other answers were either deprecated or didn't work for HttpClient 4.3.

Here is a way to allow all hostnames when building an http client.

CloseableHttpClient httpClient = HttpClients
    .custom()
    .setHostnameVerifier(new AllowAllHostnameVerifier())
    .build();

Or if you are using version 4.4 or later, the updated call looks like this:

CloseableHttpClient httpClient = HttpClients
    .custom()
    .setSSLHostnameVerifier(NoopHostnameVerifier.INSTANCE)
    .build();