Java ConcurrentHashMap损坏了值(Java ConcurrentHashMap corrupt values)

 我有一个ConcurrentHashMap，有时表现出奇怪的行为。 
 
 当我的应用程序第一次启动时，我从文件系统中读取一个目录，并使用文件名作为键将每个文件的内容加载到ConcurrentHashMap中。 某些文件可能为空，在这种情况下，我将值设置为“空”。 
 
 一旦加载了所有文件，工作线程池将等待外部请求。 当请求进来时，我调用getData（）函数，在那里我检查ConcurrentHashMap是否包含密钥。 如果密钥存在，我得到值并检查值是否为“空”。 如果value.contains（“empty”），我返回“找不到文件”。 否则，返回文件的内容。 当密钥不存在时，我尝试从文件系统加载该文件。 
 
private String getData(String name) {
    String reply = null;
    if (map.containsKey(name)) {
        reply = map.get(name);
    } else {
        reply = getDataFromFileSystem(name);
    }

    if (reply != null && !reply.contains("empty")) {
        return reply;
    }

    return "file not found";
}
 
 有时，ConcurrentHashMap将返回非空文件的内容（即value.contains("empty") == false ），但是行： 
 
if (reply != null && !reply.contains("empty")) 
 
 返回FALSE。 我将IF语句分为两部分： if (reply != null)和if (!reply.contains("empty")) 。 IF语句的第一部分返回TRUE。 第二部分返回FALSE。 所以我决定打印出变量“reply”，以确定字符串的内容是否确实包含“empty”。 这不是这种情况，即内容不包含字符串“empty”。 此外，我添加了这条线 
 
int indexOf = reply.indexOf("empty");
 
 由于变量回复在我打印出来时不包含字符串“empty”，因此我期望indexOf返回-1。 但是函数返回的值大约是字符串的长度，即if reply.length == 15100 ，则reply.indexOf("empty")返回15099。 
 
 我每周都会遇到这个问题，每周大约2-3次。 此过程每天重新启动，因此会定期重新生成ConcurrentHashMap。 
 
 有没有人在使用Java的ConcurrentHashMap时看到过这样的行为？ 
 
 编辑 
 
private String getDataFromFileSystem(String name) {
    String contents = "empty";
    try {
        File folder = new File(dir);

        File[] fileList = folder.listFiles();
        for (int i = 0; i < fileList.length; i++) {
            if (fileList[i].isFile() && fileList[i].getName().contains(name)) {
                String fileName = fileList[i].getAbsolutePath();

                FileReader fr = null;
                BufferedReader br = null;

                try {
                    fr = new FileReader(fileName);
                    br = new BufferedReader(fr);
                    String sCurrentLine;
                    while ((sCurrentLine = br.readLine()) != null) {
                        contents += sCurrentLine.trim();
                    }
                    if (contents.equals("")) {
                        contents = "empty";
                    }

                    return contents;
                } catch (Exception e) {
                    e.printStackTrace();

                    if (contents.equals("")) {
                        contents = "empty";
                    }
                    return contents;
                } finally {
                    if (fr != null) {
                        try {
                            fr.close();
                        } catch (Exception e) {
                            e.printStackTrace();
                        }
                    }

                    if (br != null) {
                        try {
                            br.close();
                        } catch (Exception e) {
                            e.printStackTrace();
                        }
                    }

                    if (map.containsKey(name)) {
                        map.remove(name);
                    }

                    map.put(name, contents);
                }
            }
        }
    } catch (Exception e) {
        e.printStackTrace();

        if (contents.equals("")) {
            contents = "empty";
        }
        return contents;
    }
    return contents;
}

I have a ConcurrentHashMap that exhibits strange behavior on occasion. 
 
When my app first starts up, I read a directory from the file system and load contents of each file into the ConcurrentHashMap using the filename as the key. Some files may be empty, in which case I set the value to "empty".
 
Once all files have been loaded, a pool of worker threads will wait for external requests. When a request comes in, I call the getData() function where I check if the ConcurrentHashMap contains the key. If the key exists I get the value and check if the value is "empty". If value.contains("empty"), I return "file not found". Otherwise, the contents of the file is returned. When the key does not exist, I try to load the file from the file system.
 
private String getData(String name) {
    String reply = null;
    if (map.containsKey(name)) {
        reply = map.get(name);
    } else {
        reply = getDataFromFileSystem(name);
    }

    if (reply != null && !reply.contains("empty")) {
        return reply;
    }

    return "file not found";
}
 
On occasion, the ConcurrentHashMap will return the contents of a non-empty file (i.e. value.contains("empty") == false), however the line:
 
if (reply != null && !reply.contains("empty")) 
 
returns FALSE. I broke down the IF statement into two parts: if (reply != null) and if (!reply.contains("empty")). The first part of the IF statement returns TRUE. The second part returns FALSE. So I decided to print out the variable "reply" in order to determine if the contents of the string does in fact contain "empty". This was NOT the case i.e. the contents did not contain the string "empty". Furthermore, I added the line 
 
int indexOf = reply.indexOf("empty");
 
Since the variable reply did not contain the string "empty" when I printed it out, I was expecting indexOf to return -1. But the function returned a value approx the length of the string i.e. if reply.length == 15100, then reply.indexOf("empty") was returning 15099.
 
I experience this issue on a weekly basis, approx 2-3 times a week. This process is restarted on a daily basis therefore the ConcurrentHashMap is re-generated regularly.
 
Has anyone seen such behavior when using Java's ConcurrentHashMap?
 
EDIT
 
private String getDataFromFileSystem(String name) {
    String contents = "empty";
    try {
        File folder = new File(dir);

        File[] fileList = folder.listFiles();
        for (int i = 0; i < fileList.length; i++) {
            if (fileList[i].isFile() && fileList[i].getName().contains(name)) {
                String fileName = fileList[i].getAbsolutePath();

                FileReader fr = null;
                BufferedReader br = null;

                try {
                    fr = new FileReader(fileName);
                    br = new BufferedReader(fr);
                    String sCurrentLine;
                    while ((sCurrentLine = br.readLine()) != null) {
                        contents += sCurrentLine.trim();
                    }
                    if (contents.equals("")) {
                        contents = "empty";
                    }

                    return contents;
                } catch (Exception e) {
                    e.printStackTrace();

                    if (contents.equals("")) {
                        contents = "empty";
                    }
                    return contents;
                } finally {
                    if (fr != null) {
                        try {
                            fr.close();
                        } catch (Exception e) {
                            e.printStackTrace();
                        }
                    }

                    if (br != null) {
                        try {
                            br.close();
                        } catch (Exception e) {
                            e.printStackTrace();
                        }
                    }

                    if (map.containsKey(name)) {
                        map.remove(name);
                    }

                    map.put(name, contents);
                }
            }
        }
    } catch (Exception e) {
        e.printStackTrace();

        if (contents.equals("")) {
            contents = "empty";
        }
        return contents;
    }
    return contents;
}

原文：https://stackoverflow.com/questions/11401197