The DiskFileItem uses a DeferredFileOutputStream which uses an in-memory byte-array that is only filled when bytes are actually transferred.
Since files are used directly and no bytes are actually copied,
the byte-array is never filled. See for yourself in the source code:
Source code CommonsMultipartFile
Source code DiskFileItem
Source code DeferredFileOutputStream
So, instead of just calling fileItem.getOutputStream();, transfer the bytes to fill the in-memory byte-array:
try (OutputStream out = fileItem.getOutputStream();
InputStream in = Files.newInputStream(file.toPath())) {
IOUtils.copy(in, dfos);
}
and then the tranferTo call will work.
This appears to be a bit cumbersome for just moving a file: CommonsMultipartFile only calls fileItem.write((File)dest) in the transferTo method.
Below are two test cases, one using the DiskFileItem and one using the LocalFileItem. The code for LocalFileItem is shown further below.
I used dependencies org.springframework:spring-web:4.2.2.RELEASE, commons-fileupload:commons-fileupload:1.3.1 and junit:junit:4.12
Test class CommonMp:
import static org.junit.Assert.*;
import java.io.*;
import java.nio.charset.*;
import java.nio.file.*;
import org.apache.commons.fileupload.disk.DiskFileItem;
import org.apache.commons.io.IOUtils;
import org.junit.Test;
import org.springframework.web.multipart.commons.CommonsMultipartFile;
public class CommonMp {
private final Charset CS = StandardCharsets.UTF_8;
@Test
public void testLocalMp() {
Path testInputFile = null, testOutputFile = null;
try {
testInputFile = prepareInputFile();
LocalFileItem lfi = new LocalFileItem(testInputFile);
CommonsMultipartFile cmf = new CommonsMultipartFile(lfi);
System.out.println("Empty: " + cmf.isEmpty());
testOutputFile = testInputFile.getParent().resolve("testMpOutput.txt");
cmf.transferTo(testOutputFile.toFile());
System.out.println("Size: " + cmf.getSize());
printOutput(testOutputFile);
} catch (Exception e) {
e.printStackTrace();
fail();
} finally {
deleteSilent(testInputFile, testOutputFile);
}
}
@Test
public void testMp() {
Path testInputFile = null, testOutputFile = null;
try {
testInputFile = prepareInputFile();
DiskFileItem di = new DiskFileItem("file", "text/plain", false, testInputFile.getFileName().toString(),
(int) Files.size(testInputFile), testInputFile.getParent().toFile());
try (OutputStream out = di.getOutputStream();
InputStream in = Files.newInputStream(testInputFile)) {
IOUtils.copy(in, out);
}
CommonsMultipartFile cmf = new CommonsMultipartFile(di);
System.out.println("Size: " + cmf.getSize());
testOutputFile = testInputFile.getParent().resolve("testMpOutput.txt");
cmf.transferTo(testOutputFile.toFile());
printOutput(testOutputFile);
} catch (Exception e) {
e.printStackTrace();
fail();
} finally {
deleteSilent(testInputFile, testOutputFile);
}
}
private Path prepareInputFile() throws IOException {
Path tmpDir = Paths.get(System.getProperty("java.io.tmpdir"));
Path testInputFile = tmpDir.resolve("testMpinput.txt");
try (OutputStream out = Files.newOutputStream(testInputFile)){
out.write("Just a test.".getBytes(CS));
}
return testInputFile;
}
private void printOutput(Path p) throws IOException {
byte[] outBytes = Files.readAllBytes(p);
System.out.println("Output: " + new String(outBytes, CS));
}
private void deleteSilent(Path... paths) {
for (Path p : paths) {
try { if (p != null) p.toFile().delete(); } catch (Exception ignored) {}
}
}
}
The custom LocalFileItem class, YMMV!
import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.UnsupportedEncodingException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.StandardCopyOption;
import org.apache.commons.fileupload.FileItem;
import org.apache.commons.fileupload.FileItemHeaders;
public class LocalFileItem implements FileItem {
private static final long serialVersionUID = 2467880290855097332L;
private final Path localFile;
public LocalFileItem(Path localFile) {
this.localFile = localFile;
}
@Override
public void write(File file) throws Exception {
Files.move(localFile, file.toPath(), StandardCopyOption.REPLACE_EXISTING);
}
@Override
public long getSize() {
// Spring's CommonsMultipartFile caches the file size and uses it to determine availability.
long size = -1L;
try {
size = Files.size(localFile);
} catch (IOException ignored) {}
return size;
}
@Override
public void delete() {
localFile.toFile().delete();
}
/* *** properties and unsupported methods *** */
private FileItemHeaders headers;
private String contentType;
private String fieldName;
private boolean formField;
@Override
public FileItemHeaders getHeaders() {
return headers;
}
@Override
public void setHeaders(FileItemHeaders headers) {
this.headers = headers;
}
@Override
public InputStream getInputStream() throws IOException {
throw new IOException("Only method write(File) is supported.");
}
public void setContentType(String contentType) {
this.contentType = contentType;
}
@Override
public String getContentType() {
return contentType;
}
@Override
public String getName() {
return localFile.getFileName().toString();
}
@Override
public boolean isInMemory() {
return false;
}
@Override
public byte[] get() {
throw new RuntimeException("Only method write(File) is supported.");
}
@Override
public String getString(String encoding)
throws UnsupportedEncodingException {
throw new RuntimeException("Only method write(File) is supported.");
}
@Override
public String getString() {
throw new RuntimeException("Only method write(File) is supported.");
}
@Override
public String getFieldName() {
return fieldName;
}
@Override
public void setFieldName(String name) {
this.fieldName = name;
}
@Override
public boolean isFormField() {
return formField;
}
@Override
public void setFormField(boolean state) {
this.formField = state;
}
@Override
public OutputStream getOutputStream() throws IOException {
throw new IOException("Only method write(File) is supported.");
}
}
