在命令提示符输入中从 BufferedReader 读取空值

Question

我正在尝试从命令行读取用户的输入。对于 filename 的输入，程序应该在检测到用户提交了空白值时退出。

但是，程序总是转到 "Inside Reading file" 代码，无论用户输入是否包含任何内容。它永远不会执行 "Program will exit now" 代码。我尝试了不同的编码方式，所有方式都得到了相同的结果。有什么问题吗？

public static void main(String[] args) throws Exception {

    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    String collection; 
    String filename;

    System.out.println("Enter the collection name: ");
    collection = br.readLine();

    String urlString = "http://localhost:8983/solr/" + collection;
    solr = new HttpSolrClient(urlString);

    doc1 = new SolrInputDocument ();

    while (true){

        System.out.println("Enter the file name: ");
        while ((filename = br.readLine()) !=null) {
            System.out.println("Inside reading file ");
            parseUsingStringTokenizer(filename);
            System.out.println("Enter the file name: ");
        }
        System.out.println("Program will exit now...");
        System.exit(0);

    }
}

Answer 1

BufferedReader returns null 当到达流的末尾时。它returns ""（长度为0的空字符串）当用户输入一个空行时。

因此，您应该将循环条件更改为：

while (!(filename = br.readLine()).equals(""))

Answer 2

添加一个额外条件 filename.trim().length()>0 和 (filename = br.readLine()) !=null。因为 != null 不会检查空格。以及为什么你把 while(true).根据您当前的代码，它是无用的。

public static void main(String[] args) throws Exception {

    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    String collection; 
    String filename;

    System.out.println("Enter the collection name: ");
    collection = br.readLine();

    String urlString = "http://localhost:8983/solr/" + collection;
    solr = new HttpSolrClient(urlString);

    doc1 = new SolrInputDocument ();

    System.out.println("Enter the file name: ");
    while ((filename = br.readLine()) !=null && filename.trim().length()>0){
        System.out.println("Inside reading file ");
        parseUsingStringTokenizer(filename);
        System.out.println("Enter the file name: ");
    }
    System.out.println("Program will exit now...");
}

在命令提示符输入中从 BufferedReader 读取空值

Reading null values from BufferedReader in command prompt input

java

bufferedreader