我想显示文件内容的预览。但不幸的是，名称与内容一起显示。我不知道如何仅打印其内容。这是一个字符串方法，因此必须回馈一些东西。而且我不能将其转换为void方法，因为它必须在System.out.println中打印，而void方法不能在System.our.printlns中打印，您可能知道。所以，你能帮我吗？
搜索“ //文件预览仅显示文件名，但不显示其内容。为什么？！”您将直接找到错误的位置。
import java.io.BufferedReader;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
public class FilesInfo {
File datei = new File(
"C:\\Users\\Elias\\Desktop\\ALLE_ORDNER\\Elias\\BACKUPKOMPLETT\\Uni Kram\\Uni Köln\\Informationsverarbeitung\\WS 2018.2019\\Java 1\\HA10");
public static void main(String[] args) {
FilesInfo main = new FilesInfo();
main.printDirInfo(
"C:\\Users\\Elias\\Desktop\\ALLE_ORDNER\\Elias\\BACKUPKOMPLETT\\Uni Kram\\Uni Köln\\Informationsverarbeitung\\WS 2018.2019\\Java 1\\HA10");
}
public void printDirInfo(String dirPath) {
File dir = new File(dirPath);
if (dir.isDirectory()) {
if (dir.list().length <= 0) {
System.out.println("Is empty!");
}
System.out.println("Direction " + dir.getName() + " contains " + dir.listFiles().length
+ " Files/Directions:");
}
else {
System.out.println(dir + " ist kein Verzeichnis!");
}
// Die einzelnen File-Objekte aus dem Verzeichnis "dir"
for (File f : dir.listFiles()) {
//File preview shows name of file together with some content.. How can I solve this problem?
System.out.println("File " + f.getName() + " | File preview: " + showPreview(f, 7) + "...");
}
}
private String showPreview(File f, int laenge) {
String name;
try {
String line;
BufferedReader br = new BufferedReader(new FileReader(f));
if ((line = br.readLine()) != null) {
System.out.println("the content preview " + line.substring(0, 5) + "...");
System.out.println();
}
} catch (FileNotFoundException e) {
System.err.println("It seems that there is no file!!");
} catch (IOException e) {
System.err.println("An error has occured while loading!");
}
name = f.getName().substring(0, laenge);
return name;
// private String showFileName() {
//
// for(dir: )
// }
}
}
console:
Direction HA10 contains 3 Files/Directions:
the content preview Java ...
File java-short.txt | File preview: java-sh...
the content preview Ein R...
File raabe.txt | File preview: raabe.t...
the content preview Dies ...
File test.txt | File preview: test.tx...
答案 0 :(得分：0)
我认为通常来说，在文本文件内容的开头显示5个字符并不能真正起到预览作用，尤其是如果第一行包含多个空格或全部为空白。如果您或您的一个应用程序正在创建这些文件，并且文件的前5个字符被视为标识字符，则这当然会有所不同。在文件创建和内容放置中已应用了特定的规则，因此只需要5个字符即可。
代码行：
System.out.println("File " + f.getName() + " | File preview: " + showPreview(f, 7) + "...");
有点令人担忧。您需要记住，正在写入控制台的 showPreview（）方法中的任何内容都将在显示上一行之前进入控制台。该方法本身还返回一个文件名，该文件名使用String＃substring（）方法被截断（laenge = length）：
name = f.getName().substring(0, laenge);
我不认为您希望这种情况发生。我相信您要返回的是实际的预览文本。我也认为您不希望showPreview（）方法在控制台中显示任何内容，至少在这种情况下，您不应该这样做。此方法的 laenge （长度）参数实际上是用来提供所需的预览长度的，这是正确的。您可能希望在控制台中显示的内容如下：
// The ShowPreview() method is passed 18 for length argument
File: java-short.txt | File Preview: This is info on sh...
File: raabe.txt | File Preview: Info on the raabe ...
File: test.txt | File Preview: Test file for this...
现在，我当然可以错了，但是如果是这种情况，那么您的方法在看起来像这样的情况下可能会更好一些：
private String showPreview(File f, int length) {
String previewText = "";
String line;
/* Try With Resourses is used to auto-close the reader. You should
always close opened files when you're done with them. */
try (BufferedReader br = new BufferedReader(new FileReader(f))) {
while ((line = br.readLine()) != null) {
line = line.trim(); // Trim of leading/trailing whitespaces or tabs, etc.
// Skip blank lines (if any).
if (line.equals("")) {
continue;
}
/* Grab first line with actual text but first make sure
there is enough text to satisfy the supplied desired
length otherwise an exception will be thrown by the
substring() method. */
if (line.length() < length) {
length = line.length();
}
previewText = line.substring(0, length) + "...";
break; // Only need the first bit of content so get outta here.
}
}
catch (FileNotFoundException ex) {
previewText = "FILE NOT FOUND!";
}
catch (IOException ex) {
previewText = "ERROR READING FILE!";
}
// If the actual file contains no preview content.
if (previewText.equals("")) {
previewText = "FILE IS EMPTY!";
}
/* Return the aquired preview text from file or
any error that may have occurred. */
return previewText;
}
下面，我提供了另一种方法来完成相同的任务，不同之处在于，它允许您提供搜索文件的目录路径（它还探索该路径中的子目录）。它还允许您提供您只想处理的文件扩展名的String []数组（提供 null 处理所有文件）。最后，它允许您提供一个整数值以指示文件内容预览的大小（以字符为单位）。文件中仅文本的第一行实际用于预览，因此，如果您提供的值是34323（例如，运气不佳），则只会得到文件中的第一行实际文本（除非没有换行符在文件中。）
这是方法：
/**
* Displays a file preview within the Console Window.<br><br>
*
* @param folderPath (String) The full path to the folder to search in.
* All Sub-directories will also be searched.<br>
*
* @param fileTypeFilter (String[] Array) Here you would supply a String
* array of the file name extensions you would like
* to process (Search for). If null is supplied or
* a zero length String[] Array then ALL files are
* processed in the supplied Folder path and any sub-
* folders contained within it. Each extension added
* to the array may or may not contain the dot so,
* either ".txt" or "txt" is considered valid.<br>
*
* @param previewCharCount (Integer) The number of characters long the preview
* text should be.<br>
*
* @return (String[] Array) All the file paths found.
*/
public String[] folderFilesPreview(String folderPath, String[] fileTypeFilter, int previewCharCount) {
String ps = File.separator;
// Gather up the desired files to preview...
File folder = new File(folderPath);
String[] filesAndFoldersList = folder.list();
if (filesAndFoldersList == null || filesAndFoldersList.length == 0) {
return null;
}
List<String> desiredFilesList = new ArrayList<>();
for (String file : filesAndFoldersList) {
File f = new File(folder.getAbsolutePath() + ps + file);
if (f.isDirectory()) {
// A sub-folder is detected. Use recursion.
String[] fafl2 = folderFilesPreview(f.getPath(), fileTypeFilter, previewCharCount);
if (fafl2 != null && fafl2.length != 0) {
desiredFilesList.addAll(Arrays.asList(fafl2));
}
}
else {
if (fileTypeFilter != null && fileTypeFilter.length > 0 && hasFileNameExtension(f.getAbsolutePath())) {
boolean isInFilterList = false;
for (String extension : fileTypeFilter) {
extension = !extension.startsWith(".") ? "." + extension : extension;
String fileExt = file.substring(file.lastIndexOf("."));
if (fileExt.equalsIgnoreCase(extension)) {
isInFilterList = true;
break;
}
}
if (isInFilterList) {
desiredFilesList.add(f.getAbsolutePath());
}
}
else {
desiredFilesList.add(f.getAbsolutePath());
}
}
}
for (int i = 0; i < desiredFilesList.size(); i++) {
String file = desiredFilesList.get(i);
String fileName = file.substring(file.lastIndexOf(File.separator) + 1);
// Read each file and display the preview...
String previewText = "";
// Try With Resourses is used to auto-close the reader.
try (BufferedReader reader = new BufferedReader(new FileReader(file))) {
String line;
while ((line = reader.readLine()) != null) {
if (line.trim().equals("")) {
continue;
}
previewText+= line.trim().length() >= previewCharCount
? line.trim().substring(0, previewCharCount) + "..."
: line.trim().substring(0) + "...";
break;
}
// If there is no content found in file...
if (previewText.equals("")) {
previewText = "FILE IS EMPTY!";
}
}
catch (FileNotFoundException ex) {
previewText = "FILE NOT FOUND!";
}
catch (IOException ex) {
previewText = "ERROR READING FILE!";
}
System.out.println("File: " + fileName + " | File preview: " + previewText);
}
return desiredFilesList.toArray(new String[0]);
}