PKIX路径构建失败：无法找到请求目标的有效认证路径

我正在使用以下客户端调用一些HTTPS网络服务：

import java.io.ByteArrayOutputStream;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.PrintStream;
import java.net.HttpURLConnection;
import java.net.URL;

import javax.net.ssl.HttpsURLConnection;

/**
 * Handles http and https connections. It sends XML request over http (or https)
 * to SOAP web service and receive the XML reply.
 * 
 * @author mhewedy
 * @date 30.10.2010
 */
public class HttpWSXmlClient
{
    private final String ws_url;
    private byte[] requestData;

    public HttpWSXmlClient(String wsUrl)
    {
        this.ws_url = wsUrl;
    }

    public void readRequest(String xmlRequestFilePath)
    {
        try
        {
            InputStream istream = new FileInputStream(xmlRequestFilePath);
            byte[] data = stream2Bytes(istream);
            istream.close();
            this.requestData = data;
        } catch (Exception e)
        {
            throw new RuntimeException(e.getMessage());
        }
    }

    /**
     * 
     * @param ps
     *            PrintStream object to send the debugging info to.
     * @return
     * @throws IOException
     */
    public byte[] sendAndRecieve(PrintStream ps) throws IOException
    {
        if (requestData == null)
            throw new RuntimeException(
                    "the request data didn't initialized yet.");
        if (ps != null)
            ps.println("Request:\n" + new String(requestData));
        URL url = new URL(ws_url);
        HttpsURLConnection connection = (HttpsURLConnection) url.openConnection();
        // or HttpURLConnection connection = (HttpURLConnection) url.openConnection();
        connection.setDoOutput(true);
        connection.setRequestProperty("content-type", "text/xml");
        connection.connect();
        OutputStream os = connection.getOutputStream();
        os.write(requestData);
        InputStream is = connection.getInputStream();
        byte[] rply = stream2Bytes(is);
        if (ps != null)
            ps.println("Response:\n" + new String(rply));
        os.close();
        is.close();
        connection.disconnect();
        return rply;
    }

    public byte[] sendAndRecieve() throws IOException
    {
        return sendAndRecieve(null);
    }

    private byte[] stream2Bytes(InputStream istream) throws IOException
    {
        ByteArrayOutputStream outstream = new ByteArrayOutputStream();
        int c;
        while ((c = istream.read()) != -1)
        {
            if (c != 0x0A && c != 0x0D) // prevent new line character from being
            // written
            {
                if (c == 0x09)
                    c = 0x20; // prevent tab character from being written,
                // instead write single space char
                outstream.write(c);
            }
        }
        byte[] ret = outstream.toByteArray();
        outstream.close();
        return ret;
    }

}

测试：

public class Test
{
    private static final String WS_URL = "https://some_server/path/to/ws";

    public static void main(String[] args) throws Exception
    {
        HttpWSXmlClient client = new HttpWSXmlClient(WS_URL);
        client.readRequest("request.xml");
        client.sendAndRecieve(System.out);
    }
}

我得到了以下输出：

Exception in thread "Main Thread" 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 com.sun.net.ssl.internal.ssl.Alerts.getSSLException(Alerts.java:174)
    at com.sun.net.ssl.internal.ssl.SSLSocketImpl.fatal(SSLSocketImpl.java:1591)
    at com.sun.net.ssl.internal.ssl.Handshaker.fatalSE(Handshaker.java:187)
    at com.sun.net.ssl.internal.ssl.Handshaker.fatalSE(Handshaker.java:181)
    at com.sun.net.ssl.internal.ssl.ClientHandshaker.serverCertificate(ClientHandshaker.java:1035)
    at com.sun.net.ssl.internal.ssl.ClientHandshaker.processMessage(ClientHandshaker.java:124)
    at com.sun.net.ssl.internal.ssl.Handshaker.processLoop(Handshaker.java:516)
    at com.sun.net.ssl.internal.ssl.Handshaker.process_record(Handshaker.java:454)
    at com.sun.net.ssl.internal.ssl.SSLSocketImpl.readRecord(SSLSocketImpl.java:884)
    at com.sun.net.ssl.internal.ssl.SSLSocketImpl.performInitialHandshake(SSLSocketImpl.java:1096)
    at com.sun.net.ssl.internal.ssl.SSLSocketImpl.startHandshake(SSLSocketImpl.java:1123)
    at com.sun.net.ssl.internal.ssl.SSLSocketImpl.startHandshake(SSLSocketImpl.java:1107)
    at sun.net.www.protocol.https.HttpsClient.afterConnect(HttpsClient.java:415)
    at sun.net.www.protocol.https.AbstractDelegateHttpsURLConnection.connect(AbstractDelegateHttpsURLConnection.java:166)
    at sun.net.www.protocol.https.HttpsURLConnectionImpl.connect(HttpsURLConnectionImpl.java:133)
    at com.se.swstest.HttpWSXmlClient.sendAndRecieve(HttpWSXmlClient.java:63)
    at com.se.swstest.Test.main(Test.java:11)
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(PKIXValidator.java:285)
    at sun.security.validator.PKIXValidator.engineValidate(PKIXValidator.java:191)
    at sun.security.validator.Validator.validate(Validator.java:218)
    at com.sun.net.ssl.internal.ssl.X509TrustManagerImpl.validate(X509TrustManagerImpl.java:126)
    at com.sun.net.ssl.internal.ssl.X509TrustManagerImpl.checkServerTrusted(X509TrustManagerImpl.java:209)
    at com.sun.net.ssl.internal.ssl.X509TrustManagerImpl.checkServerTrusted(X509TrustManagerImpl.java:249)
    at com.sun.net.ssl.internal.ssl.ClientHandshaker.serverCertificate(ClientHandshaker.java:1014)
    ... 12 more
Caused by: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
    at sun.security.provider.certpath.SunCertPathBuilder.engineBuild(SunCertPathBuilder.java:174)
    at java.security.cert.CertPathBuilder.build(CertPathBuilder.java:238)
    at sun.security.validator.PKIXValidator.doBuild(PKIXValidator.java:280)
    ... 18 more

我需要在jdk/jre/lib/security中放置证书吗？我有一个xxx_IE.crt和xxx_FX.crt（分别用于Firefox和IE），它们无法用于上述Java客户端，所以我是否需要为Java客户端获取特定的证书？
谢谢。