Restore CLI startup performance

Change InitializrService to use a late binding CloseableHttpClient
since the calling `HttpClientBuilder.create().build()` is slow.

Fixes gh-1764

spring-boot-cli/src/main/java/org/springframework/boot/cli/command/init/InitCommand.java

@@ -22,7 +22,6 @@ import java.util.Arrays;
 import joptsimple.OptionSet;
 import joptsimple.OptionSpec;
 
-import org.apache.http.impl.client.HttpClientBuilder;
 import org.springframework.boot.cli.command.Command;
 import org.springframework.boot.cli.command.OptionParsingCommand;
 import org.springframework.boot.cli.command.options.OptionHandler;
@@ -38,7 +37,7 @@ import org.springframework.boot.cli.util.Log;
 public class InitCommand extends OptionParsingCommand {
 
 	public InitCommand() {
-		this(new InitOptionHandler(getInitializrService()));
+		this(new InitOptionHandler(new InitializrService()));
 	}
 
 	public InitCommand(InitOptionHandler handler) {
@@ -46,10 +45,6 @@ public class InitCommand extends OptionParsingCommand {
 				+ "Initialzr (start.spring.io)", handler);
 	}
 
-	private static InitializrService getInitializrService() {
-		return new InitializrService(HttpClientBuilder.create().build());
-	}
-
 	static class InitOptionHandler extends OptionHandler {
 
 		private final ServiceCapabilitiesReportGenerator serviceCapabilitiesReport;

spring-boot-cli/src/main/java/org/springframework/boot/cli/command/init/InitializrService.java

@@ -28,6 +28,7 @@ import org.apache.http.client.methods.HttpGet;
 import org.apache.http.client.methods.HttpUriRequest;
 import org.apache.http.entity.ContentType;
 import org.apache.http.impl.client.CloseableHttpClient;
+import org.apache.http.impl.client.HttpClientBuilder;
 import org.apache.http.message.BasicHeader;
 import org.json.JSONException;
 import org.json.JSONObject;
@@ -47,15 +48,25 @@ class InitializrService {
 
 	private static final Charset UTF_8 = Charset.forName("UTF-8");
 
-	private final CloseableHttpClient http;
-
 	/**
-	 * Create a new instance with the given {@link CloseableHttpClient HTTP client}.
+	 * Late binding HTTP client.
 	 */
-	public InitializrService(CloseableHttpClient http) {
+	private CloseableHttpClient http;
+
+	public InitializrService() {
+	}
+
+	InitializrService(CloseableHttpClient http) {
 		this.http = http;
 	}
 
+	protected CloseableHttpClient getHttp() {
+		if (this.http == null) {
+			this.http = HttpClientBuilder.create().build();
+		}
+		return this.http;
+	}
+
 	/**
 	 * Generate a project based on the specified {@link ProjectGenerationRequest}
 	 * @return an entity defining the project
@@ -130,7 +141,7 @@ class InitializrService {
 	private CloseableHttpResponse execute(HttpUriRequest request, Object url,
 			String description) {
 		try {
-			return this.http.execute(request);
+			return getHttp().execute(request);
 		}
 		catch (IOException ex) {
 			throw new ReportableException("Failed to " + description