java version "1.7.0_45"
Hello
I am initializing the class methods in the constructor. However, the new URL(uploadUrl) will throw an exception in the constructor. So if this happens the user shouldn't be able to continue. As the constructor cannot return anything, I am wondering that is the best way to handle this?
Many thanks for any suggestions,
public class MultipleFileTransfer {
private static final String TAG = MultipartUtility.class.getSimpleName();
private DataOutputStream dataOutputStream;
private FileInputStream fileInputStream;
private HttpURLConnection httpURLConnection;
private URL url;
public MultipleFileTransfer(final String uploadUrl) {
dataOutputStream = null;
fileInputStream = null;
httpURLConnection = null;
try {
url = new URL(uploadUrl);
} catch (MalformedURLException e) {
Log.wtf(TAG, e.getMessage()); /* <-- How to handle a failure */
}
}
/* Factory method that initializes the class methods and returns the class object */
public static MultipleFileTransfer getInstance(final String uploadUrl) {
/* Check that a valid url has been entered correctly */
if(!URLUtil.isValidUrl(uploadUrl)) {
Log.wtf(TAG, "Invalid url: " + uploadUrl);
return null;
}
return new MultipleFileTransfer(uploadUrl);
}
}
As the constructor cannot return anything, I am wondering that is the best way to handle this?
Typically, allow the exception to propagate to the caller, either directly or by wrapping it in your own higher-level abstraction exception. (In your case, just allowing it directly looks more appropriate.)
public MultipleFileTransfer(final String uploadUrl) throws MalformedURLException {
// -------------------------------------------------^
dataOutputStream = null;
fileInputStream = null;
httpURLConnection = null;
url = new URL(uploadUrl);
}
Since your instance isn't useful without the URL, it makes sense for construction to fail.
Or if you want to log it in the constructor (but if it's propagating, typically any logging if appropriate would be handled by the caller):
// Logging and re-throwing, but probably not recommended
public MultipleFileTransfer(final String uploadUrl) throws MalformedURLException {
// -------------------------------------------------^
dataOutputStream = null;
fileInputStream = null;
httpURLConnection = null;
try {
url = new URL(uploadUrl);
} catch (MalformedURLException e) {
Log.wtf(TAG, e.getMessage());
throw e; // <== Rethrowing
}
}
I can think of two decent ways to handle the situation:
(1) Let the constructor throw an exception. Either rethrow the same exception after logging, or throw a different exception. If the exception it throws isn't a RuntimeException (and MalformedURLException is not a RuntimeException), you'll need to add a throws clause to the constructor.
(2) Let the constructor create an object anyway, but mark it as an "invalid" object that cannot be used. I'd add an isValid() or isInvalid() method so that the caller can query whether it's valid. Other methods should throw IllegalStateException if they're called on an invalid object.
I don't think one is clearly better than the other. It depends on preference and perhaps on the design of the rest of the program.
Related
I have the following code that reads data from a csv file that I am trying to write a unit test for. I am unsure of how to go about it.
public class BudgetTags implements BudgetTagsList{
// State variables
private Set<String> tags = new TreeSet<>();
private String tag_file_path;
public BudgetTags(String tag_file_path){
//Retrieve tags from tag file
this.tag_file_path = tag_file_path;
this.retrieveTags();
}
public void retrieveTags() {
String line = "";
try{
// Begin reading each line
BufferedReader br = new BufferedReader(new FileReader(this.tag_file_path ));
while((line = br.readLine()) != null){
String[] row = line.split(",");
this.tags.add(row[0]); //Assume correct file format
}
br.close();
} catch (IOException e){
System.out.println("Fatal exception: "+ e.getMessage());
}
}
}
Note that the method retrieveTags(); is not allowing me to specify an additional FileNotFoundException since it extends IOException. It is being tested in the following manner:
#Test
#DisplayName("File name doesn't exist")
void testRetrieveTag3() {
String path = "test\\no_file.csv";
//Instantiate new tags object
BudgetTags tags = new BudgetTags(path);
IOException thrown = assertThrows(IOException.class, () -> tags.retrieveTags());
}
The variable path does not exist so I am expecting the test to catch the IOException, (although I would prefer a FileNotFoundException) . When I run this particular test, I receive an AssertionFailedError How can I restructure my test so that it catches the FileNotFoundException when a new tags object is instantiated, since retrieveTags() is called when a new tags object is generated?
The method retrieveTags() will not allow me to specify
The method is not actually throwing the exception but catching it. What you actually need to test is that your catch block gets executed. If all you want to do on catching the exception is printing the error, test system.out can help you assert the print statement
Your assertThrows test is failing becuase it's impossible for the constructor to throw an IOException. For one, it's a checked exception, which means both the constructor and the method would require a throws IOException clause. Second, you catch the exception; it's not thrown out of the method.
Based on your test, it should look more like this:
public class BudgetTags implements BudgetTagsList {
private final Set<String> tags = new TreeSet<>();
private String tagFilePath;
public BudgetTags(String tagFilePath) throws IOException {
this.tagFilePath = tagFilePath;
retrieveTags(); // can throw IOException
}
public void retrieveTags() throws IOException {
// note: use try-with-resources to handle closing the reader
try (BufferedReader br = new BufferedReader(new FileReader(tagFilePath))) {
String line;
while ((line = br.readLine()) != null) {
String row = line.split(",");
tags.add(row[0]);
}
}
// don't catch the exception; your test indicates you want it
// thrown out to the caller
}
}
class BudgetTagsTests {
#Test
#DisplayName("File does not exist")
void testRetrieveTags3() {
String tagFilePath = "test/no_file.csv";
// note: we need to test on the constructor call, because you call
// 'retrieveTags()' in it.
assertThrows(FileNotFoundException.class, () -> new BudgetTags(tagFilePath));
}
}
By passing FileNotFoundException.class, the test will fail if any other IOException is thrown.
You should not be catching the IOException the way you are, anyway. Yes, you log it, which means if you look at the logs you'll be aware that something went wrong. But other code won't know something went wrong. To that code, it will appear as if there were simply no tags in the file. By throwing the IOException out to the caller of retrieveTags(), you're letting the caller react to the exception as needed. And if the call succeeds, but the tags are empty, then it knows the file exists but simply had no tags.
Also, you say:
Note that the method retrieveTags(); is not allowing me to specify an additional FileNotFoundException since it extends IOException.
I'm not sure what exactly you tried from that statement, but it is possible to catch more specific exceptions even though you're also catching the more general exception. It's just that the order of the catch blocks matter:
try {
somethingThatThrowsIOException();
} catch (FileNotFoundException ex) {
// do something special for when the file doesn't exist
} catch (IOException ex) {
// handle general exception
}
The more specific exception must be caught before the more general exception.
I'm calling an api to get the an input stream and then call static method parseFrom(inputstream) to convert it to the protobuffclass.
If I do it with a specific class it works:
public CustomerDTOOuterClass.CustomerDTO GetCustomer()
{
CustomerDTOOuterClass.CustomerDTO customer = null;
try
{
URL url = new URL("https://localhost:44302/Api/customer/1?");
HttpsURLConnection conn = (HttpsURLConnection)url.openConnection();
conn.setRequestMethod("GET");
conn.setRequestProperty("Content-Type", "application/x-protobuf");
conn.connect();
InputStream is = conn.getInputStream();
CustomerDTOOuterClass.CustomerDTO customer =
CustomerDTOOuterClass.CustomerDTO.parseFrom(is);
conn.disconnect();
}
catch(Exception ex)
{
System.out.println("[ "+ex.getMessage()+" ]");
}
return customer;
}
but if I change it to generic type it fails because T doesn't have the method parseFrom, is there any interface I could implement in T so I can call the parseFrom method?
public T GetObject()
{
T object = null;
try
{
URL url = new URL("https://localhost:44302/Api/customer/1?");
HttpsURLConnection conn = (HttpsURLConnection)url.openConnection();
conn.setRequestMethod("GET");
conn.setRequestProperty("Content-Type", "application/x-protobuf");
conn.connect();
InputStream is = conn.getInputStream();
T object = T.parseFrom(is);
conn.disconnect();
}
catch(Exception ex)
{
System.out.println("[ "+ex.getMessage()+" ]");
}
return object;
}
this is the error I get:
Error:(68, 27) error: cannot find symbol method parseFrom(InputStream)
Every generated protobuf type contains a static member called PARSER which is an implementation of the com.google.protobuf.Parser<T> interface. Your getObject method simply needs to take a Parser<T> as a parameter. So then you'd call it like:
Foo foo = getObject(Foo.PARSER);
If you want to do this for T, it's easier and more natural to pass the Class<T> (i.e. the class of the Proto type) into the constructor of your class, and then obtain the Parser from that like this:
public class Thing<T extends Message> {
final Parser<T> parser;
Thing(Class<T> cls) {
parser = (Parser<T>) cls.getMethod("parser").invoke(null);
}
T deserialize(byte[] bytes) {
parser.parseFrom(bytes); // try/catch etc
}
}
To expand on Kenton Varda's answer:
First I'd refactor your method into separate methods for getting the input stream and parsing it. Only the latter has any reason to be generic.
public InputStream getInputStream() {
// get it
}
Now you intend to parse the input stream and build a POJO from the protobuf. It's reasonable IMO to expect that at this point your code must be aware of what type of object you're going to get, because otherwise how would you do something intelligent with it next? E.g.
InputStream is = getInputStream();
Object o = parseGenericInputStream(is);
doSomethingWithParsedObject(o); // how to do this if you don't know o's type?
You reasonably must know o's type once you've parsed it (and therefore before you parse it), otherwise you can't do anything meaningful with it that I can think of.
So... again with credit to Kenton Varda:
public void doStuff() {
...
InputStream is = getInputStream();
MyProtobufClass pojo = parseGenericInputStream(MyProtobufClass.PARSER, is);
doSomethingWithParsedObject(pojo);
...
}
private <T> T parseGenericInputStream(Parser<T> parser, InputStream inputStream)
throws InvalidProtocolBufferException {
return parser.parseFrom(inputStream);
}
At this point though you're writing a generic method for one line of code, which is kind of not worth it if you ask me.
No, there is not; you cannot deserialize a proto without knowing its type.
If you do know its type, then you can pass in a Builder for its type, however.
(Additionally, you can't call static methods on a type variable like T.)
I'm trying to extend my library for integrating Swing and JPA by making JPA config as automatic (and portable) as can be done, and it means programmatically adding <class> elements. (I know it can be done via Hibernate's AnnotationConfiguration or EclipseLInk's ServerSession, but - portability). I'd also like to avoid using Spring just for this single purpose.
I can create a persistence.xml on the fly, and fill it with <class> elements from specified packages (via the Reflections library). The problem starts when I try to feed this persistence.xml to a JPA provider. The only way I can think of is setting up a URLClassLoader, but I can't think of a way what wouldn't make me write the file to the disk somewhere first, for sole ability to obtain a valid URL. Setting up a socket for serving the file via an URL(localhost:xxxx) seems... I don't know, evil?
Does anyone have an idea how I could solve this problem? I know it sounds like a lot of work to avoid using one library, but I'd just like to know if it can be done.
EDIT (a try at being more clear):
Dynamically generated XML is kept in a String object. I don't know how to make it available to a persistence provider. Also, I want to avoid writing the file to disk.
For purpose of my problem, a persistence provider is just a class which scans the classpath for META-INF/persistence.xml. Some implementations can be made to accept dynamic creation of XML, but there is no common interface (especially for a crucial part of the file, the <class> tags).
My idea is to set up a custom ClassLoader - if you have any other I'd be grateful, I'm not set on this one.
The only easily extendable/configurable one I could find was a URLClassLoader. It works on URL objects, and I don't know if I can create one without actually writing XML to disk first.
That's how I'm setting things up, but it's working by writing the persistenceXmlFile = new File("META-INF/persistence.xml") to disk:
Thread.currentThread().setContextClassLoader(
new URLResourceClassLoader(
new URL[] { persistenceXmlFile.toURI().toURL() },
Thread.currentThread().getContextClassLoader()
)
);
URLResourceClassLoader is URLCLassLoader's subclass, which allows for looking up resources as well as classes, by overriding public Enumeration<URL> findResources(String name).
Maybe a bit late (after 4 years), but for others that are looking for a similar solution, you may be able to use the URL factory I created:
public class InMemoryURLFactory {
public static void main(String... args) throws Exception {
URL url = InMemoryURLFactory.getInstance().build("/this/is/a/test.txt", "This is a test!");
byte[] data = IOUtils.toByteArray(url.openConnection().getInputStream());
// Prints out: This is a test!
System.out.println(new String(data));
}
private final Map<URL, byte[]> contents = new WeakHashMap<>();
private final URLStreamHandler handler = new InMemoryStreamHandler();
private static InMemoryURLFactory instance = null;
public static synchronized InMemoryURLFactory getInstance() {
if(instance == null)
instance = new InMemoryURLFactory();
return instance;
}
private InMemoryURLFactory() {
}
public URL build(String path, String data) {
try {
return build(path, data.getBytes("UTF-8"));
} catch (UnsupportedEncodingException ex) {
throw new RuntimeException(ex);
}
}
public URL build(String path, byte[] data) {
try {
URL url = new URL("memory", "", -1, path, handler);
contents.put(url, data);
return url;
} catch (MalformedURLException ex) {
throw new RuntimeException(ex);
}
}
private class InMemoryStreamHandler extends URLStreamHandler {
#Override
protected URLConnection openConnection(URL u) throws IOException {
if(!u.getProtocol().equals("memory")) {
throw new IOException("Cannot handle protocol: " + u.getProtocol());
}
return new URLConnection(u) {
private byte[] data = null;
#Override
public void connect() throws IOException {
initDataIfNeeded();
checkDataAvailability();
// Protected field from superclass
connected = true;
}
#Override
public long getContentLengthLong() {
initDataIfNeeded();
if(data == null)
return 0;
return data.length;
}
#Override
public InputStream getInputStream() throws IOException {
initDataIfNeeded();
checkDataAvailability();
return new ByteArrayInputStream(data);
}
private void initDataIfNeeded() {
if(data == null)
data = contents.get(u);
}
private void checkDataAvailability() throws IOException {
if(data == null)
throw new IOException("In-memory data cannot be found for: " + u.getPath());
}
};
}
}
}
We can use the Jimfs google library for that.
First, we need to add the maven dependency to our project:
<dependency>
<groupId>com.google.jimfs</groupId>
<artifactId>jimfs</artifactId>
<version>1.2</version>
</dependency>
After that, we need to configure our filesystem behavior, and write our String content to the in-memory file, like this:
public static final String INPUT =
"\n"
+ "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n"
+ "<note>\n"
+ " <to>Tove</to>\n"
+ " <from>Jani</from>\n"
+ " <heading>Reminder</heading>\n"
+ " <body>Don't forget me this weekend!</body>\n"
+ "</note>";
#Test
void usingJIMFS() throws IOException {
try (var fs = Jimfs.newFileSystem(Configuration.unix())) {
var path = fs.getPath(UUID.randomUUID().toString());
Files.writeString(path, INPUT);
var url = path.toUri().toURL();
assertThat(url.getProtocol()).isEqualTo("jimfs");
assertThat(Resources.asCharSource(url, UTF_8).read()).isEqualTo(INPUT);
}
}
We can find more examples in the official repository.
If we look inside the jimfs source code we will find the implementation is similar to #NSV answer.
I have the following class:
public class FileLoader {
private Map<Brand, String> termsOfUseText = new HashMap<Brand, String>();
public void load() {
for (Brand brand : Brand.values()) {
readAndStoreTermsOfUseForBrand(brand);
}
}
private void readAndStoreTermsOfUseForBrand(Brand brand) {
String resourceName = "termsOfUse/" + brand.name().toLowerCase() + ".txt";
InputStream in = this.getClass().getClassLoader().getResourceAsStream(resourceName);
try {
String content = IOUtils.toString(in);
termsOfUseText.put(brand, content);
} catch (IOException e) {
throw new IllegalStateException(String.format("Failed to find terms of use source file %s", resourceName),e);
}
}
public String getTextForBrand(Brand brand) {
return termsOfUseText.get(brand);
}
}
Brand is an enum, and I need all the valid .txt files to be on the classpath. How do I make the IOException occur, given that the Brand enum contains all the valid brands and therfore all the .txt files for them exist?
Suggestions around refactoring the current code are welcome if it makes it more testable!
Three options I see right off:
Use PowerMock to mock IOUtils.toString(). I consider PowerMock to be quite a last resort. I'd rather refactor the source to something a little more test-friendly.
Extract the IOUtils call to a protected method. Create a test-specific subclass of your class that overrides this method and throws the IOException.
Extract the InputStream creation to a protected method. Create a test-specific subclass to override the method and return a mock InputStream.
I would suggest a bit of refactoring. All your methods are void, this usually means they are not functional.
For example, you can extract this functionality:
private String readTermsOfUseForBrand(InputStream termsOfUserIs) {
try {
String content = IOUtils.toString(in);
return content;
} catch (IOException e) {
throw new IllegalStateException(String.format("Failed to find terms of use source file %s", resourceName), e);
}
return null;
}
So that we can assert on the String result in our tests.
Of course this is not functional code, as it reads from an Input Stream. And it does so with IOUtils.toString() method that cannot be mocked easily (well, there's PowerMock but as Ryan Stewart said it's the last resort).
To test IO exceptions you can create a failing input stream (tested with JDK7):
public class FailingInputStream extends InputStream {
#Override
public int read() throws IOException {
throw new IOException("Test generated exception");
}
}
And test like that:
#Test
public void testReadTermsOfUseForBrand() {
FileLoader instance = new FileLoader();
String result = instance.readTermsOfUseForBrand(new FailingInputStream());
assertNull(result);
}
Missing file will cause NullPointerException because getResourceAsStream will return null and you will have in==null. IOException in this case may actually be pretty rare. If it's critical for you to see it, I can only think of instrumenting this code to throw it if code is executed in test scope. But is it really that important?
I would use a mock to accomplish this.
Example (untested, just to give you some thought):
#Test(expected=IllegalStateException.class)
public void testThrowIOException() {
PowerMockito.mockStatic(IOUtils.class);
PowerMockito.when(IOUtils.toString()).thenThrow(
new IOException("fake IOException"));
FileLoader fileLoader = new FileLoader();
Whitebox.invokeMethod(fileLoader,
"readAndStoreTermsOfUseForBrand", new Brand(...));
// If IllegalStateException is not thrown then this test case fails (see "expected" above)
}
Code below is completely untested
To cause the IOException use:
FileInputStream in = this.getClass().getClassLoader().getResourceAsStream(resourceName);
in.mark(0);
//read some data
in.reset(); //IOException
To test the IOException case use:
void test
{
boolean success = false;
try
{
//code to force ioException
}
catch(IOException ioex)
{
success = true;
}
assertTrue(success);
}
In JUnit4
#Test(expected=IOException.class)
void test
{
//code to force ioException
}
Other JUnit
void test
{
try
{
//code to force IOException
fail("If this gets hit IO did not occur, fail test");
}
catch(IOException ioex)
{
//success!
}
}
I am working with java.
I have one url as a input.I am trying to open url using java code.
I am using:
URL url=new URL("http://doctorwho.time-and-space.co.uk/index.php");
URLConnection conn=url.openConnection();
InputStream in=conn.getInputStream();
here I have passed one link as a input,but this website is unavailable.Here I want to throw an
exception on opening this url,but it is not throwing any exception,it is executing properly.
Please help me,how to catch this exception if website is unavailable.
Actually all of your lines can throw an exception:
java.net.URL.openConnection() throws IOException
java.net.URLConnection.getInputStream() throws IOException
java.net.URLConnection.getInputStream() throws IOException
You should handle these one by one, and if you encounter any of them, you should deal with the error in your own code. Maybe throw another exception, stop execution, anything you want. Probably you have a big try-catch (Exception e) around this block, which you should get rid of.
If you want to throw an exception, and not handling it in the function, use throws, and don't use try-catch:
public void foo() throws IOException
{
URL url=new URL("http://doctorwho.time-and-space.co.uk/index.php");
URLConnection conn=url.openConnection();
InputStream in=conn.getInputStream();
//...
}
You can wrap the IOException into your own.
public void fireURL(String pathToFireParam) throws CustomException
{
try{
URL url=new URL(pathToFireParam);
URLConnection conn=url.openConnection();
InputStream in=conn.getInputStream();
} catch(IOException ioexc){
throw new CustomException("Unavailable: "+ioexc.getMessage(),ioexc);
}
}
This code is indeed throwing an exception: IOException.
The best thing probably is to create an Exception class specific to this service that you recatch. To let the program take differents actions depending of the error (this can be just displaying a nice looking message instead of an hugly stacktrace), you can extends your base service exception with the specific exception.
So the base Exception :
public class MyServiceException extends Exception {
private static final long serialVersionUID = 1L;
public MyServiceException(String s, Throwable throwable) {
super(s, throwable);
}
}
The Exception that is thrown for all problem related to "stuff"
public class MyServiceStufFailedException extends MyServiceException {
private static final long serialVersionUID = 1L;
public MyServiceStufFailedException(String s, Throwable throwable) {
super(s, throwable);
}
}
And the code that load the XML file :
private void doStufWithURL(String fileURL) throws MyServiceStufFailedException {
try {
URL url=new URL(fileURL);
URLConnection conn=url.openConnection();
InputStream in=conn.getInputStream();
// Use input Stream too...
} catch (IOException exception) {
//Don't forget to put an explanation and the cause to help while debugging.
throw new MyServiceStufFailedException("IO Error while reading " + fileURL, exception);
}
}