"PKIX路径构建失败" 和 "无法找到请求目标的有效认证路径"

我正在尝试在我的Java项目中使用twitter4j库获取推文，在底层使用的是java.net.HttpURLConnection(如堆栈跟踪所示)。在第一次运行时，我遇到了关于证书sun.security.validator.ValidatorException和sun.security.provider.certpath.SunCertPathBuilderException的错误。然后我通过以下方式添加了Twitter证书：

C:\Program Files\Java\jdk1.7.0_45\jre\lib\security>keytool -importcert -trustcacerts -file PathToCert -alias ca_alias -keystore "C:\Program Files\Java\jdk1.7.0_45\jre\lib\security\cacerts"

但是没有成功。这里是获取推文的过程：

public static void main(String[] args) throws TwitterException {
    ConfigurationBuilder cb = new ConfigurationBuilder();
    cb.setDebugEnabled(true)
        .setOAuthConsumerKey("myConsumerKey")
        .setOAuthConsumerSecret("myConsumerSecret")
        .setOAuthAccessToken("myAccessToken")
        .setOAuthAccessTokenSecret("myAccessTokenSecret");
    
    TwitterFactory tf = new TwitterFactory(cb.build());
    Twitter twitter = tf.getInstance();
    
    try {
        Query query = new Query("iphone");
        QueryResult result;
        result = twitter.search(query);
        System.out.println("Total amount of tweets: " + result.getTweets().size());
        List<Status> tweets = result.getTweets();
        
        for (Status tweet : tweets) {
            System.out.println("@" + tweet.getUser().getScreenName() + " : " + tweet.getText());
        }
    } catch (TwitterException te) {
        te.printStackTrace();
        System.out.println("Failed to search tweets: " + te.getMessage());
    }

这里是错误：

sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
Relevant discussions can be found on the Internet at:
    http://www.google.co.jp/search?q=d35baff5 or
    http://www.google.co.jp/search?q=1446302e
TwitterException{exceptionCode=[d35baff5-1446302e 43208640-747fd158 43208640-747fd158 43208640-747fd158], statusCode=-1, message=null, code=-1, retryAfter=-1, rateLimitStatus=null, version=3.0.5}
    at twitter4j.internal.http.HttpClientImpl.request(HttpClientImpl.java:177)
    at twitter4j.internal.http.HttpClientWrapper.request(HttpClientWrapper.java:61)
    at twitter4j.internal.http.HttpClientWrapper.get(HttpClientWrapper.java:81)
    at twitter4j.TwitterImpl.get(TwitterImpl.java:1929)
    at twitter4j.TwitterImpl.search(TwitterImpl.java:306)
    at jku.cc.servlets.TweetsAnalyzer.main(TweetsAnalyzer.java:38)
Caused by: javax.net.ssl.SSLHandshakeException: sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
    at sun.security.ssl.Alerts.getSSLException(Unknown Source)
    at sun.security.ssl.SSLSocketImpl.fatal(Unknown Source)
    at sun.security.ssl.Handshaker.fatalSE(Unknown Source)
    at sun.security.ssl.Handshaker.fatalSE(Unknown Source)
    at sun.security.ssl.ClientHandshaker.serverCertificate(Unknown Source)
    at sun.security.ssl.ClientHandshaker.processMessage(Unknown Source)
    at sun.security.ssl.Handshaker.processLoop(Unknown Source)
    at sun.security.ssl.Handshaker.process_record(Unknown Source)
    at sun.security.ssl.SSLSocketImpl.readRecord(Unknown Source)
    at sun.security.ssl.SSLSocketImpl.performInitialHandshake(Unknown Source)
    at sun.security.ssl.SSLSocketImpl.startHandshake(Unknown Source)
    at sun.security.ssl.SSLSocketImpl.startHandshake(Unknown Source)
    at sun.net.www.protocol.https.HttpsClient.afterConnect(Unknown Source)
    at sun.net.www.protocol.https.AbstractDelegateHttpsURLConnection.connect(Unknown Source)
    at sun.net.www.protocol.http.HttpURLConnection.getInputStream(Unknown Source)
    at java.net.HttpURLConnection.getResponseCode(Unknown Source)
    at sun.net.www.protocol.https.HttpsURLConnectionImpl.getResponseCode(Unknown Source)
    at twitter4j.internal.http.HttpResponseImpl.<init>(HttpResponseImpl.java:34)
    at twitter4j.internal.http.HttpClientImpl.request(HttpClientImpl.java:141)
    ... 5 more
Caused by: sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
    at sun.security.validator.PKIXValidator.doBuild(Unknown Source)
    at sun.security.validator.PKIXValidator.engineValidate(Unknown Source)
    at sun.security.validator.Validator.validate(Unknown Source)
    at sun.security.ssl.X509TrustManagerImpl.validate(Unknown Source)
    at sun.security.ssl.X509TrustManagerImpl.checkTrusted(Unknown Source)
    at sun.security.ssl.X509TrustManagerImpl.checkServerTrusted(Unknown Source)
    ... 20 more
Caused by: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
    at sun.security.provider.certpath.SunCertPathBuilder.engineBuild(Unknown Source)
    at java.security.cert.CertPathBuilder.build(Unknown Source)
    ... 26 more
Failed to search tweets: sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target