how to get size of file in mb?

问题

I have a file on a server and it is a zip file. How to check if the file size is bigger than 27 MB?

File file = new File("U:\intranet_root\intranet\R1112B2.zip");
if (file > 27) {
   //do something
}

回答1:

Use the length() method of the File class to return the size of the file in bytes.

// Get file from file name
File file = new File("U:\intranet_root\intranet\R1112B2.zip");

// Get length of file in bytes
long fileSizeInBytes = file.length();
// Convert the bytes to Kilobytes (1 KB = 1024 Bytes)
long fileSizeInKB = fileSizeInBytes / 1024;
// Convert the KB to MegaBytes (1 MB = 1024 KBytes)
long fileSizeInMB = fileSizeInKB / 1024;

if (fileSizeInMB > 27) {
  ...
}

You could combine the conversion into one step, but I've tried to fully illustrate the process.

回答2:

Try following code:

File file = new File("infilename");

// Get the number of bytes in the file
long sizeInBytes = file.length();
//transform in MB
long sizeInMb = sizeInBytes / (1024 * 1024);

回答3:

Example :

public static String getStringSizeLengthFile(long size) {

    DecimalFormat df = new DecimalFormat("0.00");

    float sizeKb = 1024.0f;
    float sizeMb = sizeKb * sizeKb;
    float sizeGb = sizeMb * sizeKb;
    float sizeTerra = sizeGb * sizeKb;


    if(size < sizeMb)
        return df.format(size / sizeKb)+ " Kb";
    else if(size < sizeGb)
        return df.format(size / sizeMb) + " Mb";
    else if(size < sizeTerra)
        return df.format(size / sizeGb) + " Gb";

    return "";
}

回答4:

Easiest is by using FileUtils from Apache commons-io.( https://commons.apache.org/proper/commons-io/javadocs/api-2.5/org/apache/commons/io/FileUtils.html )

Returns human readable file size from Bytes to Exabytes , rounding down to the boundary.

File fileObj = new File(filePathString);
String fileSizeReadable = FileUtils.byteCountToDisplaySize(fileObj.length());

// output will be like 56 MB

回答5:

file.length() will return you the length in bytes, then you divide that by 1048576, and now you've got megabytes!

回答6:

You can retrieve the length of the file with File#length(), which will return a value in bytes, so you need to divide this by 1024*1024 to get its value in mb.

回答7:

Since Java 7 you can use java.nio.file.Files.size(Path p).

Path path = Paths.get("C:\\1.txt");

long expectedSizeInMB = 27;
long expectedSizeInBytes = 1024 * 1024 * expectedSizeInMB;

long sizeInBytes = -1;
try {
    sizeInBytes = Files.size(path);
} catch (IOException e) {
    System.err.println("Cannot get the size - " + e);
    return;
}

if (sizeInBytes > expectedSizeInBytes) {
    System.out.println("Bigger than " + expectedSizeInMB + " MB");
} else {
    System.out.println("Not bigger than " + expectedSizeInMB + " MB");
}

回答8:

public static long sizeOf(File file)

More info on API : http://commons.apache.org/proper/commons-io/apidocs/org/apache/commons/io/FileUtils.html

回答9:

You can use substring to get portio of String which is equal to 1 mb:

public static void main(String[] args) {
        // Get length of String in bytes
        String string = "long string";
        long sizeInBytes = string.getBytes().length;
        int oneMb=1024*1024;
        if (sizeInBytes>oneMb) {
          String string1Mb=string.substring(0, oneMb);
        }
    }

回答10:

You can use FileChannel in Java.

FileChannel has the size() method to determine the size of the file.

    String fileName = "D://words.txt";

    Path filePath = Paths.get(fileName);

    FileChannel fileChannel = FileChannel.open(filePath);
    long fileSize = fileChannel.size();

    System.out.format("The size of the file: %d bytes", fileSize);

Or you can determine the file size using Apache Commons' FileUtils' sizeOf() method. If you are using maven, add this to pom.xml file.

<dependency>
    <groupId>commons-io</groupId>
    <artifactId>commons-io</artifactId>
    <version>2.6</version>
</dependency>

Try the following coding,

    String fileName = "D://words.txt";
    File f = new File(fileName);

    long fileSize = FileUtils.sizeOf(f);        

    System.out.format("The size of the file: %d bytes", fileSize);

These methods will output the size in Bytes. So to get the MB size, you need to divide the file size from (1024*1024).

Now you can simply use the if-else conditions since the size is captured in MB.

来源：https://stackoverflow.com/questions/8989746/how-to-get-size-of-file-in-mb

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