Java-Mail 用QQ邮箱发送邮件时报错

Java端报错信息如下：

javax.mail.MessagingException: Could not connect to SMTP host: smtp.qq.com, port: 465;

  nested exception is:

	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.mail.smtp.SMTPTransport.openServer(SMTPTransport.java:1961)

	at com.sun.mail.smtp.SMTPTransport.protocolConnect(SMTPTransport.java:654)

	at javax.mail.Service.connect(Service.java:295)

	at javax.mail.Service.connect(Service.java:176)

	at javax.mail.Service.connect(Service.java:196)

	at org.jxstar.service.mail.MailUtil.sendBase(Unknown Source)

	at org.jxstar.service.mail.MailThread.run(Unknown Source)

	at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:885)

	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:907)

	at java.lang.Thread.run(Thread.java:619)

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 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:975)

	at com.sun.net.ssl.internal.ssl.ClientHandshaker.processMessage(ClientHandshaker.java:123)

	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 com.sun.mail.util.SocketFetcher.configureSSLSocket(SocketFetcher.java:549)

	at com.sun.mail.util.SocketFetcher.createSocket(SocketFetcher.java:354)

	at com.sun.mail.util.SocketFetcher.getSocket(SocketFetcher.java:211)

	at com.sun.mail.smtp.SMTPTransport.openServer(SMTPTransport.java:1927)

	... 9 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(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:954)

	... 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(SunCertPathBuilder.java:174)

	at java.security.cert.CertPathBuilder.build(CertPathBuilder.java:238)

	at sun.security.validator.PKIXValidator.doBuild(PKIXValidator.java:280)

	... 26 more

原因分析：
    这种问题有时会出现，有时又不会出现，原因是需要下载一个证书到 \jre\lib\security  目录中。
通过如下的java代码查看当前java环境的目录：
System.out.println(System.getProperty("java.home"));
显示效果类似：
C:\Program Files (x86)\Java\jdk1.6.0_03\jre
 
 
证书生成方法：
参考此文 https://blog.csdn.net/frankche ... 64939
1、通过下图导出证书：



2、切换到jre的/lib/security/下，注意JRE路径别弄错了。
执行如下命令
keytool -import -alias mailqqcom -keystore cacerts -file c://mailqqcom.crt

库密钥口令输入：changeit

是否信任输入：Y

最后显示导入成功！再执行发送邮件的类，执行成功。