diff --git a/src/configurationProvider.ts b/src/configurationProvider.ts
index 7ec94e3..7a9979e 100644
--- a/src/configurationProvider.ts
+++ b/src/configurationProvider.ts
@@ -1,264 +1,280 @@
-// Copyright (c) Microsoft Corporation. All rights reserved.
-// Licensed under the MIT license.
-
-import * as vscode from "vscode";
-import TelemetryReporter from "vscode-extension-telemetry";
-import * as commands from "./commands";
-
-export class JavaDebugConfigurationProvider implements vscode.DebugConfigurationProvider {
-    private isUserSettingsDirty: boolean = true;
-    constructor(private _reporter: TelemetryReporter) {
-        vscode.workspace.onDidChangeConfiguration((event) => {
-            if (vscode.debug.activeDebugSession) {
-                this.isUserSettingsDirty = false;
-                return updateDebugSettings();
-            } else {
-                this.isUserSettingsDirty = true;
-            }
-        });
-    }
-
-    // Returns an initial debug configurations based on contextual information.
-    public provideDebugConfigurations(folder: vscode.WorkspaceFolder | undefined, token?: vscode.CancellationToken):
-        vscode.ProviderResult<vscode.DebugConfiguration[]> {
-        return <Thenable<vscode.DebugConfiguration[]>>this.provideDebugConfigurationsAsync(folder);
-    }
-
-    // Try to add all missing attributes to the debug configuration being launched.
-    public resolveDebugConfiguration(folder: vscode.WorkspaceFolder | undefined, config: vscode.DebugConfiguration, token?: vscode.CancellationToken):
-        vscode.ProviderResult<vscode.DebugConfiguration> {
-        return this.heuristicallyResolveDebugConfiguration(folder, config);
-    }
-
-    private provideDebugConfigurationsAsync(folder: vscode.WorkspaceFolder | undefined, token?: vscode.CancellationToken) {
-        return vscode.window.withProgress({location: vscode.ProgressLocation.Window}, (p) => {
-            return new Promise((resolve, reject) => {
-                p.report({message: "Auto generating configuration..."});
-                resolveMainClass(folder ? folder.uri : undefined).then((res: any[]) => {
-                    let cache;
-                    cache = {};
-                    const launchConfigs = res.map((item) => {
-                        return {
-                            type: "java",
-                            name: this.constructLaunchConfigName(item.mainClass, item.projectName, cache),
-                            request: "launch",
-                            // tslint:disable-next-line
-                            cwd: "${workspaceFolder}",
-                            console: "internalConsole",
-                            stopOnEntry: false,
-                            mainClass: item.mainClass,
-                            projectName: item.projectName,
-                            args: "",
-                        };
-                    });
-                    resolve([...launchConfigs, {
-                        type: "java",
-                        name: "Debug (Attach)",
-                        request: "attach",
-                        hostName: "localhost",
-                        port: 0,
-                    }]);
-                }, (ex) => {
-                    p.report({message: `failed to generate configuration. ${ex}`});
-                    reject(ex);
-                });
-            });
-        });
-    }
-
-    private constructLaunchConfigName(mainClass: string, projectName: string, cache: {}) {
-        const prefix = "Debug (Launch)-";
-        let name = prefix + mainClass.substr(mainClass.lastIndexOf(".") + 1);
-        if (projectName !== undefined) {
-            name += `<${projectName}>`;
-        }
-        if (cache[name] === undefined) {
-            cache[name] = 0;
-            return name;
-        } else {
-            cache[name] += 1;
-            return `${name}(${cache[name]})`;
-        }
-    }
-
-    private async heuristicallyResolveDebugConfiguration(folder: vscode.WorkspaceFolder | undefined, config: vscode.DebugConfiguration) {
-        try {
-            if (this.isUserSettingsDirty) {
-                this.isUserSettingsDirty = false;
-                await updateDebugSettings();
-            }
-
-            if (Object.keys(config).length === 0) { // No launch.json in current workspace.
-                // check whether it is opened as a folder
-                if (folder !== undefined) {
-                    // for opened with folder, return directly.
-                    return config;
-                }
-                // only rebuild for single file case before the build error issue is resolved.
-                try {
-                    const buildResult = await vscode.commands.executeCommand(commands.JAVA_BUILD_WORKSPACE, false);
-                    console.log(buildResult);
-                } catch (err) {
-                    const ans = await vscode.window.showErrorMessage("Build failed, do you want to continue?", "Proceed", "Abort");
-                    if (ans !== "Proceed") {
-                        return undefined;
-                    }
-                }
-                // Generate config in memory for single file
-                config.type = "java";
-                config.name = "Java Debug";
-                config.request = "launch";
-            }
-
-            if (config.request === "launch") {
-                if (!config.mainClass) {
-                    const res = <any[]>(await resolveMainClass(folder ? folder.uri : undefined));
-                    if (res.length === 0) {
-                        vscode.window.showErrorMessage(
-                            "Cannot resolve main class automatically, please specify the mainClass " +
-                            "(e.g. [mymodule/]com.xyz.MainClass) in the launch.json.");
-                        return;
-                    }
-                    const pickItems = res.map((item) => {
-                        let name = item.mainClass;
-                        let details = `main class: ${item.mainClass}`;
-                        if (item.projectName !== undefined) {
-                            name += `<${item.projectName}>`;
-                            details += ` | project name: ${item.projectName}`;
-                        }
-                        return {
-                            description: details,
-                            label: name,
-                            item,
-                        };
-                    }).sort ((a, b): number => {
-                        return a.label > b.label ? 1 : -1;
-                    });
-                    const selection = await vscode.window.showQuickPick(pickItems, { placeHolder: "Select main class<project name>" });
-                    if (selection) {
-                        config.mainClass = selection.item.mainClass;
-                        config.projectName = selection.item.projectName;
-                    } else {
-                        vscode.window.showErrorMessage("Please specify the mainClass (e.g. [mymodule/]com.xyz.MainClass) in the launch.json.");
-                        this.log("usageError", "Please specify the mainClass (e.g. [mymodule/]com.xyz.MainClass) in the launch.json.");
-                        return undefined;
-                    }
-                }
-                if (this.isEmptyArray(config.classPaths) && this.isEmptyArray(config.modulePaths)) {
-                    const result = <any[]>(await resolveClasspath(config.mainClass, config.projectName));
-                    config.modulePaths = result[0];
-                    config.classPaths = result[1];
-                }
-                if (this.isEmptyArray(config.classPaths) && this.isEmptyArray(config.modulePaths)) {
-                    const hintMessage = "Cannot resolve the modulepaths/classpaths automatically, please specify the value in the launch.json.";
-                    vscode.window.showErrorMessage(hintMessage);
-                    this.log("usageError", hintMessage);
-                    return undefined;
-                }
-            } else if (config.request === "attach") {
-                if (!config.hostName || !config.port) {
-                    vscode.window.showErrorMessage("Please specify the host name and the port of the remote debuggee in the launch.json.");
-                    this.log("usageError", "Please specify the host name and the port of the remote debuggee in the launch.json.");
-                    return undefined;
-                }
-            } else {
-                const ans = await vscode.window.showErrorMessage(
-                    // tslint:disable-next-line:max-line-length
-                    "Request type \"" + config.request + "\" is not supported. Only \"launch\" and \"attach\" are supported.", "Open launch.json");
-                if (ans === "Open launch.json") {
-                    await vscode.commands.executeCommand(commands.VSCODE_ADD_DEBUGCONFIGURATION);
-                }
-                this.log("usageError", "Illegal request type in launch.json");
-                return undefined;
-            }
-            const debugServerPort = await startDebugSession();
-            if (debugServerPort) {
-                config.debugServer = debugServerPort;
-                return config;
-            } else {
-                this.log("exception", "Failed to start debug server.");
-                // Information for diagnostic:
-                console.log("Cannot find a port for debugging session");
-                return undefined;
-            }
-        } catch (ex) {
-            const errorMessage = (ex && ex.message) || ex;
-            vscode.window.showErrorMessage(String(errorMessage));
-            if (this._reporter) {
-                const exception = (ex && ex.data && ex.data.cause)
-                    || { stackTrace: [], detailMessage: String((ex && ex.message) || ex || "Unknown exception") };
-                const properties = {
-                    message: "",
-                    stackTrace: "",
-                };
-                if (exception && typeof exception === "object") {
-                    properties.message = exception.detailMessage;
-                    properties.stackTrace = (Array.isArray(exception.stackTrace) && JSON.stringify(exception.stackTrace))
-                        || String(exception.stackTrace);
-                } else {
-                    properties.message = String(exception);
-                }
-                this._reporter.sendTelemetryEvent("exception", properties);
-            }
-            return undefined;
-        }
-    }
-
-    private log(type: string, message: string) {
-        if (this._reporter) {
-            this._reporter.sendTelemetryEvent(type, { message });
-        }
-    }
-
-    private isEmptyArray(configItems: any): boolean {
-        return !Array.isArray(configItems) || !configItems.length;
-    }
-}
-
-function startDebugSession() {
-    return commands.executeJavaLanguageServerCommand(commands.JAVA_START_DEBUGSESSION);
-}
-
-function resolveClasspath(mainClass, projectName) {
-    return commands.executeJavaLanguageServerCommand(commands.JAVA_RESOLVE_CLASSPATH, mainClass, projectName);
-}
-
-function resolveMainClass(workspaceUri: vscode.Uri) {
-    if (workspaceUri) {
-        return commands.executeJavaLanguageServerCommand(commands.JAVA_RESOLVE_MAINCLASS, workspaceUri.toString());
-    }
-    return commands.executeJavaLanguageServerCommand(commands.JAVA_RESOLVE_MAINCLASS);
-}
-
-async function updateDebugSettings() {
-    const debugSettingsRoot: vscode.WorkspaceConfiguration = vscode.workspace.getConfiguration("java.debug");
-    if (!debugSettingsRoot) {
-        return;
-    }
-    const logLevel = convertLogLevel(debugSettingsRoot.logLevel || "");
-    if (debugSettingsRoot.settings && Object.keys(debugSettingsRoot.settings).length) {
-        try {
-            console.log("settings:", await commands.executeJavaLanguageServerCommand(commands.JAVA_UPDATE_DEBUG_SETTINGS, JSON.stringify(
-                { ...debugSettingsRoot.settings, logLevel })));
-        } catch (err) {
-            // log a warning message and continue, since update settings failure should not block debug session
-            console.log("Cannot update debug settings.", err)
-        }
-    }
-}
-
-function convertLogLevel(commonLogLevel: string) {
-    // convert common log level to java log level
-    switch (commonLogLevel.toLowerCase()) {
-        case "verbose":
-            return "FINE";
-        case "warn":
-            return "WARNING";
-        case "error":
-            return "SEVERE";
-        case "info":
-            return "INFO";
-        default:
-            return "FINE";
-    }
-}
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT license.
+
+import * as vscode from "vscode";
+import TelemetryReporter from "vscode-extension-telemetry";
+import * as commands from "./commands";
+
+export class JavaDebugConfigurationProvider implements vscode.DebugConfigurationProvider {
+    private isUserSettingsDirty: boolean = true;
+    constructor(private _reporter: TelemetryReporter) {
+        vscode.workspace.onDidChangeConfiguration((event) => {
+            if (vscode.debug.activeDebugSession) {
+                this.isUserSettingsDirty = false;
+                return updateDebugSettings();
+            } else {
+                this.isUserSettingsDirty = true;
+            }
+        });
+    }
+
+    // Returns an initial debug configurations based on contextual information.
+    public provideDebugConfigurations(folder: vscode.WorkspaceFolder | undefined, token?: vscode.CancellationToken):
+        vscode.ProviderResult<vscode.DebugConfiguration[]> {
+        return <Thenable<vscode.DebugConfiguration[]>>this.provideDebugConfigurationsAsync(folder);
+    }
+
+    // Try to add all missing attributes to the debug configuration being launched.
+    public resolveDebugConfiguration(folder: vscode.WorkspaceFolder | undefined, config: vscode.DebugConfiguration, token?: vscode.CancellationToken):
+        vscode.ProviderResult<vscode.DebugConfiguration> {
+        return this.heuristicallyResolveDebugConfiguration(folder, config);
+    }
+
+    private provideDebugConfigurationsAsync(folder: vscode.WorkspaceFolder | undefined, token?: vscode.CancellationToken) {
+        return vscode.window.withProgress({location: vscode.ProgressLocation.Window}, (p) => {
+            return new Promise((resolve, reject) => {
+                p.report({message: "Auto generating configuration..."});
+                resolveMainClass(folder ? folder.uri : undefined).then((res: IMainClassOption []) => {
+                    let cache;
+                    cache = {};
+                    const launchConfigs = res.map((item) => {
+                        return {
+                            type: "java",
+                            name: this.constructLaunchConfigName(item.mainClass, item.projectName, cache),
+                            request: "launch",
+                            // tslint:disable-next-line
+                            cwd: "${workspaceFolder}",
+                            console: "internalConsole",
+                            stopOnEntry: false,
+                            mainClass: item.mainClass,
+                            projectName: item.projectName,
+                            args: "",
+                        };
+                    });
+                    resolve([...launchConfigs, {
+                        type: "java",
+                        name: "Debug (Attach)",
+                        request: "attach",
+                        hostName: "localhost",
+                        port: 0,
+                    }]);
+                }, (ex) => {
+                    p.report({message: `failed to generate configuration. ${ex}`});
+                    reject(ex);
+                });
+            });
+        });
+    }
+
+    private constructLaunchConfigName(mainClass: string, projectName: string, cache: {}) {
+        const prefix = "Debug (Launch)-";
+        let name = prefix + mainClass.substr(mainClass.lastIndexOf(".") + 1);
+        if (projectName !== undefined) {
+            name += `<${projectName}>`;
+        }
+        if (cache[name] === undefined) {
+            cache[name] = 0;
+            return name;
+        } else {
+            cache[name] += 1;
+            return `${name}(${cache[name]})`;
+        }
+    }
+
+    private async heuristicallyResolveDebugConfiguration(folder: vscode.WorkspaceFolder | undefined, config: vscode.DebugConfiguration) {
+        try {
+            if (this.isUserSettingsDirty) {
+                this.isUserSettingsDirty = false;
+                await updateDebugSettings();
+            }
+
+            if (Object.keys(config).length === 0) { // No launch.json in current workspace.
+                // check whether it is opened as a folder
+                if (folder !== undefined) {
+                    // for opened with folder, return directly.
+                    return config;
+                }
+                // only rebuild for single file case before the build error issue is resolved.
+                try {
+                    const buildResult = await vscode.commands.executeCommand(commands.JAVA_BUILD_WORKSPACE, false);
+                    console.log(buildResult);
+                } catch (err) {
+                    const ans = await vscode.window.showErrorMessage("Build failed, do you want to continue?", "Proceed", "Abort");
+                    if (ans !== "Proceed") {
+                        return undefined;
+                    }
+                }
+                // Generate config in memory for single file
+                config.type = "java";
+                config.name = "Java Debug";
+                config.request = "launch";
+            }
+
+            if (config.request === "launch") {
+                if (!config.mainClass) {
+                    const userSelection = await chooseMainClass(folder);
+                    if (!userSelection || !userSelection.mainClass) {
+                        // the error is handled inside chooseMainClass
+                        return;
+                    }
+                    config.mainClass = userSelection.mainClass;
+                    config.projectName  = userSelection.projectName;
+                }
+                if (this.isEmptyArray(config.classPaths) && this.isEmptyArray(config.modulePaths)) {
+                    const result = <any[]>(await resolveClasspath(config.mainClass, config.projectName));
+                    config.modulePaths = result[0];
+                    config.classPaths = result[1];
+                }
+                if (this.isEmptyArray(config.classPaths) && this.isEmptyArray(config.modulePaths)) {
+                    const hintMessage = "Cannot resolve the modulepaths/classpaths automatically, please specify the value in the launch.json.";
+                    vscode.window.showErrorMessage(hintMessage);
+                    this.log("usageError", hintMessage);
+                    return undefined;
+                }
+            } else if (config.request === "attach") {
+                if (!config.hostName || !config.port) {
+                    vscode.window.showErrorMessage("Please specify the host name and the port of the remote debuggee in the launch.json.");
+                    this.log("usageError", "Please specify the host name and the port of the remote debuggee in the launch.json.");
+                    return undefined;
+                }
+            } else {
+                const ans = await vscode.window.showErrorMessage(
+                    // tslint:disable-next-line:max-line-length
+                    "Request type \"" + config.request + "\" is not supported. Only \"launch\" and \"attach\" are supported.", "Open launch.json");
+                if (ans === "Open launch.json") {
+                    await vscode.commands.executeCommand(commands.VSCODE_ADD_DEBUGCONFIGURATION);
+                }
+                this.log("usageError", "Illegal request type in launch.json");
+                return undefined;
+            }
+            const debugServerPort = await startDebugSession();
+            if (debugServerPort) {
+                config.debugServer = debugServerPort;
+                return config;
+            } else {
+                this.log("exception", "Failed to start debug server.");
+                // Information for diagnostic:
+                console.log("Cannot find a port for debugging session");
+                return undefined;
+            }
+        } catch (ex) {
+            const errorMessage = (ex && ex.message) || ex;
+            vscode.window.showErrorMessage(String(errorMessage));
+            if (this._reporter) {
+                const exception = (ex && ex.data && ex.data.cause)
+                    || { stackTrace: [], detailMessage: String((ex && ex.message) || ex || "Unknown exception") };
+                const properties = {
+                    message: "",
+                    stackTrace: "",
+                };
+                if (exception && typeof exception === "object") {
+                    properties.message = exception.detailMessage;
+                    properties.stackTrace = (Array.isArray(exception.stackTrace) && JSON.stringify(exception.stackTrace))
+                        || String(exception.stackTrace);
+                } else {
+                    properties.message = String(exception);
+                }
+                this._reporter.sendTelemetryEvent("exception", properties);
+            }
+            return undefined;
+        }
+    }
+
+    private log(type: string, message: string) {
+        if (this._reporter) {
+            this._reporter.sendTelemetryEvent(type, { message });
+        }
+    }
+
+    private isEmptyArray(configItems: any): boolean {
+        return !Array.isArray(configItems) || !configItems.length;
+    }
+}
+
+function startDebugSession() {
+    return commands.executeJavaLanguageServerCommand(commands.JAVA_START_DEBUGSESSION);
+}
+
+function resolveClasspath(mainClass, projectName) {
+    return commands.executeJavaLanguageServerCommand(commands.JAVA_RESOLVE_CLASSPATH, mainClass, projectName);
+}
+
+function resolveMainClass(workspaceUri: vscode.Uri): Promise<IMainClassOption[]> {
+    if (workspaceUri) {
+        return <Promise<IMainClassOption[]>>commands.executeJavaLanguageServerCommand(commands.JAVA_RESOLVE_MAINCLASS, workspaceUri.toString());
+    }
+    return <Promise<IMainClassOption[]>>commands.executeJavaLanguageServerCommand(commands.JAVA_RESOLVE_MAINCLASS);
+}
+
+async function updateDebugSettings() {
+    const debugSettingsRoot: vscode.WorkspaceConfiguration = vscode.workspace.getConfiguration("java.debug");
+    if (!debugSettingsRoot) {
+        return;
+    }
+    const logLevel = convertLogLevel(debugSettingsRoot.logLevel || "");
+    if (debugSettingsRoot.settings && Object.keys(debugSettingsRoot.settings).length) {
+        try {
+            console.log("settings:", await commands.executeJavaLanguageServerCommand(commands.JAVA_UPDATE_DEBUG_SETTINGS, JSON.stringify(
+                { ...debugSettingsRoot.settings, logLevel })));
+        } catch (err) {
+            // log a warning message and continue, since update settings failure should not block debug session
+            console.log("Cannot update debug settings.", err)
+        }
+    }
+}
+
+function convertLogLevel(commonLogLevel: string) {
+    // convert common log level to java log level
+    switch (commonLogLevel.toLowerCase()) {
+        case "verbose":
+            return "FINE";
+        case "warn":
+            return "WARNING";
+        case "error":
+            return "SEVERE";
+        case "info":
+            return "INFO";
+        default:
+            return "FINE";
+    }
+}
+
+interface IMainClassOption {
+    readonly projectName?: string;
+    readonly mainClass: string;
+}
+
+async function chooseMainClass(folder: vscode.WorkspaceFolder | undefined): Promise<IMainClassOption> {
+    const res = await resolveMainClass(folder ? folder.uri : undefined);
+    const pickItems = res.map((item) => {
+        let name = item.mainClass;
+        let details = `main class: ${item.mainClass}`;
+        if (item.projectName !== undefined) {
+            name += `<${item.projectName}>`;
+            details += ` | project name: ${item.projectName}`;
+        }
+        return {
+            description: details,
+            label: name,
+            item,
+        };
+    }).sort ((a, b): number => {
+        return a.label > b.label ? 1 : -1;
+    });
+    if (pickItems.length === 0) {
+        vscode.window.showErrorMessage(
+            "Cannot resolve main class automatically, please specify the mainClass " +
+            "(e.g. [mymodule/]com.xyz.MainClass) in the launch.json.");
+        return;
+    }
+    const selection = pickItems.length > 1 ?
+        await vscode.window.showQuickPick(pickItems, { placeHolder: "Select main class<project name>" })
+        : pickItems[0];
+    if (selection && selection.item) {
+        return selection.item;
+    } else {
+        vscode.window.showErrorMessage("Please specify the mainClass (e.g. [mymodule/]com.xyz.MainClass) in the launch.json.");
+        this.log("usageError", "Please specify the mainClass (e.g. [mymodule/]com.xyz.MainClass) in the launch.json.");
+        return undefined;
+    }
+}