"java.net.UnknownHostException" Displayed When Compiling Spring Boot

Symptom

The message "java.net.UnknownHostException" is displayed when "self-signed.badssl.com" is accessed during the Spring Boot compilation.

Key Process and Cause Analysis

The host is not mapped. Add proxy configurations to solve the problem.

Conclusion and Solution

1. Open the ReactiveCloudFoundrySecurityService.java file.

   vim ./spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/cloudfoundry/reactive/ReactiveCloudFoundrySecurityService.java

2. Press i to enter the insert mode and modify the file.
   1. Add the following content below line 27:

      import reactor.netty.tcp.ProxyProvider;

      

   2. Insert the following code in line 64:

      else {
                               HttpClient client = HttpClient.create().tcpConfiguration(tcpClient -> {
                                        tcpClient = tcpClient.proxy(proxy -> proxy.type(ProxyProvider.Proxy.HTTP).host("127.0.0.1")
                                                        .port(3128).nonProxyHosts("localhost|my*.com").build());
                                        return tcpClient;
                                });
                                webClientBuilder.clientConnector(new ReactorClientHttpConnector(client));
                       }

      In the preceding example, 127.0.0.1 and 3128 indicate the IP address and port number of the proxy host. Replace them with the actual ones.

      

   3. Modify the content in line 77 as follows:

              HttpClient client = HttpClient.create().tcpConfiguration(tcpClient -> {
                                tcpClient = tcpClient.proxy(proxy -> proxy.type(ProxyProvider.Proxy.HTTP).host("127.0.0.1").port(3128)
                                                .nonProxyHosts("localhost|my*.com").build());
                                return tcpClient;
                        }).secure((sslContextSpec) -> sslContextSpec.sslContext(createSslContext()));
                        return new ReactorClientHttpConnector(client);

      In the preceding example, 127.0.0.1 and 3128 indicate the IP address and port number of the proxy host. Replace them with the actual ones.

      

      

      Run the :set list command to check the format. Spaces are not allowed. Use Tab to indent the code.

3. Press Esc, type :wq!, and press Enter to save the file and exit.
4. Recompile Spring Boot.