feat(java): refactor code to use runReadAction and replace string operation

The code has been refactored to use `runReadAction` for better performance when working with PSI elements. The string replacement operation has been changed to ensure that the new code is inserted at the beginning of the document instead of after the last class, which was the previous behavior. This commit also includes the import statements for `PsiElementFactory` and `PsiJavaFile` within the `runReadAction` block to ensure that they are executed during the read action.

Author: phodal

java/src/main/kotlin/cc/unitmesh/idea/context/JavaCodeModifier.kt

@@ -11,11 +11,7 @@ import com.intellij.openapi.diagnostic.logger
 import com.intellij.openapi.project.Project
 import com.intellij.openapi.project.guessProjectDir
 import com.intellij.openapi.vfs.VirtualFile
-import com.intellij.psi.PsiDocumentManager
-import com.intellij.psi.PsiElementFactory
-import com.intellij.psi.PsiJavaFile
-import com.intellij.psi.PsiManager
-import com.intellij.psi.PsiMethod
+import com.intellij.psi.*
 
 open class JavaCodeModifier : CodeModifier {
     companion object {
@@ -43,19 +39,28 @@ open class JavaCodeModifier : CodeModifier {
 
         val isFullCode = trimCode.startsWith("import") && trimCode.contains("class ")
         // check is sourceFile has class
-        val classes = runReadAction {
-            val psiJavaFile = lookupFile(project, sourceFile)
-            psiJavaFile.classes
-        }
+        val classes = runReadAction { lookupFile(project, sourceFile).classes }
 
         if (classes.isNotEmpty()) {
-            // replace the last class with the new test class
             val lastClass = classes.last()
             val classEndOffset = lastClass.textRange.endOffset
 
+            val newCode = try {
+                runReadAction {
+                    val createFileFromText =
+                        PsiFileFactory.getInstance(project)
+                            .createFileFromText("Test.java", JavaLanguage.INSTANCE, trimCode)
+
+                    createFileFromText?.text ?: trimCode
+                }
+            } catch (e: Throwable) {
+                log.warn("Failed to create file from text: $trimCode", e)
+                trimCode
+            }
+
             WriteCommandAction.runWriteCommandAction(project) {
                 val document = PsiDocumentManager.getInstance(project).getDocument(lastClass.containingFile)
-                document?.replaceString(classEndOffset, document.textLength, trimCode)
+                document?.replaceString(0, classEndOffset, newCode)
             }
 
             return true