title: how to resolve jsoup error: unable to find valid certification path to requested target
body: <p>I am trying to parse the html of the following URL:</p>
  
  <p><a href="https://www.smuc.ac.kr/mbs/smuc/jsp/board/list.jsp?boardId=6993&amp;id=smuc_040100000000" rel="noreferrer">https://www.smuc.ac.kr/mbs/smuc/jsp/board/list.jsp?boardId=6993&amp;id=smuc_040100000000</a></p>
  
  <p>I'm getting the following error:</p>
  
  <pre><code>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(PKIXValidator.java:387)
      at sun.security.validator.PKIXValidator.engineValidate(PKIXValidator.java:292)
      at sun.security.validator.Validator.validate(Validator.java:260)
      at sun.security.ssl.X509TrustManagerImpl.validate(X509TrustManagerImpl.java:324)
      at sun.security.ssl.X509TrustManagerImpl.checkTrusted(X509TrustManagerImpl.java:229)
      at sun.security.ssl.X509TrustManagerImpl.checkServerTrusted(X509TrustManagerImpl.java:124)
      at sun.security.ssl.ClientHandshaker.serverCertificate(ClientHandshaker.java:1491)
      ... 15 more
  Caused by: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
      at sun.security.provider.certpath.SunCertPathBuilder.build(SunCertPathBuilder.java:141)
      at sun.security.provider.certpath.SunCertPathBuilder.engineBuild(SunCertPathBuilder.java:126)
      at java.security.cert.CertPathBuilder.build(CertPathBuilder.java:280)
      at sun.security.validator.PKIXValidator.doBuild(PKIXValidator.java:382)
      ... 21 more
  </code></pre>
  
  <p><br/> This is my code:</p>
  
  <pre><code>public class MainActivity extends AppCompatActivity {
      private ListView listView;
      private TextView textView;
      public ArrayList&lt;String&gt; arrayList = new ArrayList&lt;String&gt;();
      private ArrayAdapter&lt;String&gt; arrayAdapter;
  
      @Override
      protected void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
          setContentView(R.layout.activity_main);
          listView = (ListView) findViewById(R.id.listView);
          new Insert().execute();
          arrayAdapter = new ArrayAdapter&lt;String&gt;(MainActivity.this, R.layout.list_ok, R.id.text, arrayList );
         }
  
      class Insert extends AsyncTask&lt;String, Void, String&gt; {
          @Override
          protected String doInBackground(String... params) {
              try {
                 // Connection.Response res = Jsoup.connect("https://www.smuc.ac.kr/mbs/smuc/index.jsp")
                 //         .method(Connection.Method.POST)
                 //         .execute();
                  Document document = Jsoup.connect("https://www.smuc.ac.kr/mbs/smuc/jsp/board/list.jsp?boardId=6993&amp;id=smuc_040100000000").get();
                  Elements elements = document.select(".tit");
                  arrayList.clear();
                  for (Element element : elements) {
                      arrayList.add(element.text());
                  }
              } catch (IOException e) {
                  e.printStackTrace();
              }
              return null;
          }
          @Override
          protected void onPostExecute(String result){
              listView.setAdapter(arrayAdapter);
          }
  
      }
  
  }
  </code></pre>