HttpGet with HTTPS : SSLPeerUnverifiedException

Using HttpClient 3.x, you need to do this:

Protocol easyHttps = new Protocol("https", new EasySSLProtocolSocketFactory(), 443);
Protocol.registerProtocol("https", easyHttps);

An implementation of EasySSLProtocolSocketFactory can be found here.

Note: Do not do this in production code, use http instead, or the actual self signed public key as suggested above.

On HttpClient 4.xx:

import static org.junit.Assert.assertEquals;

import java.security.KeyManagementException;
import java.security.NoSuchAlgorithmException;
import java.security.cert.X509Certificate;

import javax.net.ssl.SSLContext;
import javax.net.ssl.TrustManager;
import javax.net.ssl.X509TrustManager;

import org.apache.http.HttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.conn.scheme.Scheme;
import org.apache.http.conn.ssl.SSLSocketFactory;
import org.apache.http.impl.client.DefaultHttpClient;
import org.junit.Test;

public class HttpClientTrustingAllCertsTest {

    @Test
    public void shouldAcceptUnsafeCerts() throws Exception {
        DefaultHttpClient httpclient = httpClientTrustingAllSSLCerts();
        HttpGet httpGet = new HttpGet("https://host_with_self_signed_cert");
        HttpResponse response = httpclient.execute( httpGet );
        assertEquals("HTTP/1.1 200 OK", response.getStatusLine().toString());
    }

    private DefaultHttpClient httpClientTrustingAllSSLCerts() throws NoSuchAlgorithmException, KeyManagementException {
        DefaultHttpClient httpclient = new DefaultHttpClient();

        SSLContext sc = SSLContext.getInstance("SSL");
        sc.init(null, getTrustingManager(), new java.security.SecureRandom());

        SSLSocketFactory socketFactory = new SSLSocketFactory(sc);
        Scheme sch = new Scheme("https", 443, socketFactory);
        httpclient.getConnectionManager().getSchemeRegistry().register(sch);
        return httpclient;
    }

    private TrustManager[] getTrustingManager() {
        TrustManager[] trustAllCerts = new TrustManager[] { new X509TrustManager() {
            @Override
            public java.security.cert.X509Certificate[] getAcceptedIssuers() {
                return null;
            }

            @Override
            public void checkClientTrusted(X509Certificate[] certs, String authType) {
                // Do nothing
            }

            @Override
            public void checkServerTrusted(X509Certificate[] certs, String authType) {
                // Do nothing
            }

        } };
        return trustAllCerts;
    }
}

This answer follows on to owlstead and Mat's responses. It applies to SE/EE installations, not ME/mobile/Android SSL.

Since no one has yet mentioned it, I'll mention the "production way" to fix this: Follow the steps from the AuthSSLProtocolSocketFactory class in HttpClient to update your trust store & key stores.

1. Import a trusted certificate and generate a truststore file

keytool -import -alias "my server cert" -file server.crt -keystore my.truststore

2. Generate a new key (use the same password as the truststore)

keytool -genkey -v -alias "my client key" -validity 365 -keystore my.keystore

3. Issue a certificate signing request (CSR)

keytool -certreq -alias "my client key" -file mycertreq.csr -keystore my.keystore

4. (self-sign or get your cert signed)

5. Import the trusted CA root certificate

keytool -import -alias "my trusted ca" -file caroot.crt -keystore my.keystore

6. Import the PKCS#7 file containg the complete certificate chain

keytool -import -alias "my client key" -file mycert.p7 -keystore my.keystore

7. Verify the resultant keystore file's contents

keytool -list -v -keystore my.keystore

If you don't have a server certificate, generate one in JKS format, then export it as a CRT file. Source: keytool documentation

keytool -genkey -alias server-alias -keyalg RSA -keypass changeit
    -storepass changeit -keystore my.keystore

keytool -export -alias server-alias -storepass changeit
    -file server.crt -keystore my.keystore