fix: Show welcome view when no Java projects in workspace

package.json

@@ -369,12 +369,12 @@
         },
         {
           "command": "java.view.package.exportJar",
-          "when": "view == javaProjectExplorer && java:serverMode == Standard && workspaceFolderCount != 0",
+          "when": "view == javaProjectExplorer && java:serverMode == Standard && !java:noJavaProjects",
           "group": "navigation@20"
         },
         {
           "command": "java.view.package.refresh",
-          "when": "view == javaProjectExplorer && java:serverMode == Standard",
+          "when": "view == javaProjectExplorer && java:serverMode == Standard && !java:noJavaProjects",
           "group": "navigation@30"
         },
         {
@@ -399,12 +399,12 @@
         },
         {
           "command": "java.project.build.workspace",
-          "when": "view == javaProjectExplorer && java:serverMode == Standard && workspaceFolderCount != 0",
+          "when": "view == javaProjectExplorer && java:serverMode == Standard && !java:noJavaProjects",
           "group": "overflow_20@10"
         },
         {
           "command": "java.project.clean.workspace",
-          "when": "view == javaProjectExplorer && java:serverMode == Standard && workspaceFolderCount != 0",
+          "when": "view == javaProjectExplorer && java:serverMode == Standard && !java:noJavaProjects",
           "group": "overflow_20@20"
         }
       ],
@@ -519,6 +519,11 @@
         "contents": "%viewsWelcome.workbench.createNewJavaProject%",
         "when": "workspaceFolderCount == 0"
       },
+      {
+        "view": "javaProjectExplorer",
+        "contents": "%viewsWelcome.workbench.noJavaProject%",
+        "when": "java:noJavaProjects"
+      },
       {
         "view": "javaProjectExplorer",
         "contents": "%viewsWelcome.workbench.inLightWeightMode%",

package.nls.json

@@ -37,6 +37,7 @@
   "taskDefinitions.java.project.exportJar.testCompileOutput": "The folders containing output class files in the test scope.",
   "taskDefinitions.java.project.exportJar.dependencies": "The artifact dependencies in the runtime scope.",
   "taskDefinitions.java.project.exportJar.testDependencies": "The artifact dependencies in the test scope.",
-  "viewsWelcome.workbench.createNewJavaProject": "You can also [open a Java project](command:_java.project.open), or create a new Java project by clicking the below button.\n[Create Java Project](command:java.project.create)",
+  "viewsWelcome.workbench.createNewJavaProject": "You can also [open a Java project](command:_java.project.open), or create a new Java project by clicking the button below.\n[Create Java Project](command:java.project.create)",
+  "viewsWelcome.workbench.noJavaProject": "No Java projects found in the current workspace. You can [open a Java project](command:_java.project.open), or create a new Java project by clicking the button below.\n[Create Java Project](command:java.project.create)",
   "viewsWelcome.workbench.inLightWeightMode": "No projects are listed because the Java Language Server is currently running in [LightWeight Mode](https://aka.ms/vscode-java-lightweight). To show projects, click on the button to switch to Standard Mode.\n[Switch to Standard Mode](command:java.server.mode.switch?%5B%22Standard%22,true%5D)"
 }

package.nls.zh.json

@@ -38,5 +38,6 @@
   "taskDefinitions.java.project.exportJar.dependencies": "在 runtime scope 内的依赖。",
   "taskDefinitions.java.project.exportJar.testDependencies": "在 test scope 内的依赖。",
   "viewsWelcome.workbench.createNewJavaProject": "您也可以[打开一个 Java 项目](command:_java.project.open)，或点击下方按钮创建一个新的 Java 项目。\n[创建 Java 项目](command:java.project.create)",
+  "viewsWelcome.workbench.noJavaProject": "当前工作空间未发现 Java 项目，您可以[打开一个 Java 项目](command:_java.project.open)，或点击下方按钮创建一个新的 Java 项目。\n[创建 Java 项目](command:java.project.create)",
   "viewsWelcome.workbench.inLightWeightMode": "由于 Java 语言服务正运行在 [LightWeight 模式](https://aka.ms/vscode-java-lightweight)下，因此项目将不会展示在该视图中。如果您需要展示项目信息，可以点击下方按钮将 Java 语言服务切换至 Standard 模式。\n[切换至 Standard 模式](command:java.server.mode.switch?%5B%22Standard%22,true%5D)"
 }

src/constants.ts

@@ -4,6 +4,7 @@
 export namespace Context {
     export const EXTENSION_ACTIVATED: string = "java:projectManagerActivated";
     export const SUPPORTED_BUILD_FILES: string = "java:supportedBuildFiles";
+    export const NO_JAVA_PEOJECT: string = "java:noJavaProjects";
 }
 
 export namespace Explorer {

src/views/dependencyDataProvider.ts

@@ -7,7 +7,9 @@ import {
     RelativePattern, TreeDataProvider, TreeItem, Uri, window, workspace,
 } from "vscode";
 import { instrumentOperation, instrumentOperationAsVsCodeCommand } from "vscode-extension-telemetry-wrapper";
+import { contextManager } from "../../extension.bundle";
 import { Commands } from "../commands";
+import { Context } from "../constants";
 import { newJavaClass, newPackage } from "../explorerCommands/new";
 import { executeExportJarTask } from "../exportJarSteps/ExportJarTaskProvider";
 import { Jdtls } from "../java/jdtls";
@@ -168,18 +170,16 @@ export class DependencyDataProvider implements TreeDataProvider<ExplorerNode> {
                         kind: NodeKind.Workspace,
                     }, undefined)));
                     this._rootItems = rootItems;
-                    return rootItems;
                 } else {
                     const result: INodeData[] = await Jdtls.getProjects(folders[0].uri.toString());
                     result.forEach((project) => {
                         rootItems.push(new ProjectNode(project, undefined));
                     });
                     this._rootItems = rootItems;
-                    return rootItems;
                 }
-            } else {
-                throw new Error("No workspace folder found, please open a folder into the workspace first.");
             }
+            contextManager.setContextValue(Context.NO_JAVA_PEOJECT, _.isEmpty(rootItems));
+            return rootItems;
         } finally {
             this._lock.release();
         }