Java not able to validate certificate even if certificate valid in browser

I have one GET API to call using java and I have used feign client to call this API.

When I call this API it is giving the error:

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 java.base/sun.security.validator.PKIXValidator.doBuild(PKIXValidator.java:439)
    at java.base/sun.security.validator.PKIXValidator.engineValidate(PKIXValidator.java:306)
    at java.base/sun.security.validator.Validator.validate(Validator.java:264)
    at java.base/sun.security.ssl.X509TrustManagerImpl.validate(X509TrustManagerImpl.java:313)
    at java.base/sun.security.ssl.X509TrustManagerImpl.checkTrusted(X509TrustManagerImpl.java:222)
    at java.base/sun.security.ssl.X509TrustManagerImpl.checkServerTrusted(X509TrustManagerImpl.java:129)
    at java.base/sun.security.ssl.CertificateMessage$T13CertificateConsumer.checkServerCerts(CertificateMessage.java:1323)
    ... 18 more
Caused by: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
    at java.base/sun.security.provider.certpath.SunCertPathBuilder.build(SunCertPathBuilder.java:141)
    at java.base/sun.security.provider.certpath.SunCertPathBuilder.engineBuild(SunCertPathBuilder.java:126)
    at java.base/java.security.cert.CertPathBuilder.build(CertPathBuilder.java:297)
    at java.base/sun.security.validator.PKIXValidator.doBuild(PKIXValidator.java:434)

When I hit the same API in the browser, it is working fine. Browser doesn't display like an untrusted connection.

certificate information from firefox:

I am running my application in docker image openjdk:11-slim.

Why java is not able to validate the certificate even if the certificate is valid?

This may be because they are not added to your cacerts -

You can try running installCerts from below link, for the URL of site which you are trying to downlaod certificate from or which is not being allowed to access because of certificate issue.

java --source 11 InstallCert.java 

https://github.com/escline/InstallCert

If it is self signed certificate, try below in your DockerFile -

FROM openjdk:11-jdk-slim
WORKDIR /opt/workdir/

#.crt file in the same folder as your Dockerfile
ARG CERT="certificate.crt"

#import cert into java
COPY $CERT /opt/workdir/
RUN keytool -importcert -file $CERT -alias $CERT -cacerts -storepass changeit -noprompt

If you have the .cer file, which you can otherwise export from browser. Add below to your DockerFile. So the required certs are available before ssl handshake. -

ADD your_ca_root.crt /usr/local/share/ca-certificates/foo.crt
RUN chmod 644 /usr/local/share/ca-certificates/foo.crt && update-ca-certificates