I have a JSP-Page which contains the following
<td>${MyClass.mymethod(false)}</td>
and MyClass contains the following:
public static String mymethod(boolean param)
{
//...
}
public static String mymethod(String param)
{
//...
}
Now when I display the JSP-Page mymethod(String param) is called. How can I make the false a boolean value?
Method names being put in a Map as keys.So there is no function overloading in el.or try giving different names for function in xml.
Related
Assuming that we have an object with the following attributes:
public class MyObject {
private String attr1;
private Integer attr2;
//...
public String getAttr1() {
return this.attr1;
}
public Integer getAttr2() {
return this.attr2;
}
}
One way of sorting a list mylist of this object, based on its attribute attr1 is:
mylist.sort(Comparator.comparing(MyObject::getAttr1));
Is it possible to use this code inside a method in a dynamic way and replace the getAttr1 part with a method that returns the getter of an attribute of the object based on its name? Something like:
public void sortListByAttr(List<MyObject> list, String attr) {
list.sort(Comparator.comparing(MyObject::getGetterByAttr(attr)));
}
The MyObject::getGetterByAttr(attr) part does not compile, I wrote it just as an example to explain my idea
I tried to implement a method with the following code new PropertyDescriptor(attr, MyObject.class).getReadMethod().invoke(new MyObject()) but It's still not possible to call a method with a parameter from the comparing method
You could add a method like
public static Function<MyObject,Object> getGetterByAttr(String s) {
switch(s) {
case "attr1": return MyObject::getAttr1;
case "attr2": return MyObject::getAttr2;
}
throw new IllegalArgumentException(s);
}
to your class, but the returned function is not suitable for Comparator.comparing, as it expects a type fulfilling U extends Comparable<? super U> and while each of String and Integer is capable of fulfilling this constraint in an individual invocation, there is no way to declare a generic return type for getGetterByAttr to allow both type and be still compatible with the declaration of comparing.
An alternative would be a factory for complete Comparators.
public static Comparator<MyObject> getComparator(String s) {
switch(s) {
case "attr1": return Comparator.comparing(MyObject::getAttr1);
case "attr2": return Comparator.comparing(MyObject::getAttr2);
}
throw new IllegalArgumentException(s);
}
to be used like
public void sortListByAttr(List<MyObject> list, String attr) {
list.sort(getComparator(attr));
}
This has the advantage that it also may support properties whose type is not Comparable and requires a custom Comparator. Also, more efficient comparators for primitive types (e.g. using comparingInt) would be possible.
You may also consider using a Map instead of switch:
private static Map<String,Comparator<MyObject>> COMPARATORS;
static {
Map<String,Comparator<MyObject>> comparators=new HashMap<>();
comparators.put("attr1", Comparator.comparing(MyObject::getAttr1));
comparators.put("attr2", Comparator.comparing(MyObject::getAttr2));
COMPARATORS = Collections.unmodifiableMap(comparators);
}
public static Comparator<MyObject> getComparator(String s) {
Comparator<MyObject> comparator = COMPARATORS.get(s);
if(comparator != null) return comparator;
throw new IllegalArgumentException(s);
}
More dynamic is only possible via Reflection, but this would complicate the code, add a lot of potential error source, with only little benefit, considering that you need only to add one line of source code for adding support for another property in either of the examples above. After all, the set of defined properties gets fixed at compile time.
You could also have a single place where this comparators would be defined:
static enum MyObjectComparator {
ATTR1("attr1", Comparator.comparing(MyObject::getAttr1));
MyObjectComparator(String attrName, Comparator<MyObject> comparator) {
this.comparator = comparator;
this.attrName = attrName;
}
private final Comparator<MyObject> comparator;
private final String attrName;
private static MyObjectComparator[] allValues = MyObjectComparator.values();
public static Comparator<MyObject> findByValue(String value) {
return Arrays.stream(allValues)
.filter(x -> x.attrName.equalsIgnoreCase(value))
.map(x -> x.comparator)
.findAny()
.orElseThrow(RuntimeException::new);
}
}
And your usage would be:
public void sortListByAttr(List<MyObject> list, String attr) {
list.sort(MyObjectComparator.findByValue(attr));
}
I am trying to create a class that abstracts the use of predicates from its end user.
My app uses Guava-Retrying extension which works great.
Retryer<Boolean> retryer = RetryerBuilder.<Boolean>newBuilder()
.retryIfResult(Predicates.<Boolean>isNull())
....
.build();
retryer.call(callable);
I can call easily call it with predicates and it polls until predicate returns false.
Now, maybe I misunderstand predicates but I am trying to create a class that will abstract them.
I wish to call it as follows
MyPoller.poll(new PollCondition<MyClass>() {
#Override public boolean condition() {
return !isValid(result**.getPermissions(), permissionName);
}
});
So I wrote PollCondition class as follows.
public abstract class PollCondition<T> {
public Predicate<T> getCondition() {
return result -> condition();
}
public abstract boolean condition();
}
but MyPoller.poll() call fail to compile - result is not declared.
Any idea?
It seems you don't understand predicates indeed. A predicate is a function that takes an input as argument, and returns a boolean value (usually based on the input, of course).
Let's examine your PollCondition class:
public abstract class PollCondition<T> {
public Predicate<T> getCondition() {
return result -> condition();
}
public abstract boolean condition();
}
So it defines an abstract condition() method that doesn't take anything as argument, and returns a boolean. And it can be "transformed" into a Predicate using getCondition(). This method returns a predicate which takes an input as argument (result), ignores it completely, and always returns the boolean returned by condition().
You then create a PollCondition using
new PollCondition<MyClass>() {
#Override public boolean condition() {
return !isValid(result.getPermissions(), permissionName);
}
}
That would be correct if, in the scope where you execute that code, there was a variable named result. But there is not. resultis in fact an input to your condition. So the class should in fact defined like this:
public abstract class PollCondition<T> {
public Predicate<T> getCondition() {
return result -> condition(result);
}
public abstract boolean condition(T result);
}
And you would then be able to instantiate one using
new PollCondition<MyClass>() {
#Override public boolean condition(MyClass result) {
return !isValid(result.getPermissions(), permissionName);
}
}
But I really, really don't see what that brings over using a simple Predicate directly.
Define MyPoller.poll() like this:
public poll(Predicate<T> predicate);
and use it like this:
MyPoller.poll(result -> !isValid(result.getPermissions(), permissionName));
Spring MVC support request parameter to javabean. But when I want to bind boolean,
It is still not work in javabean.
If the code in controller is:
public void test(#RequestParam(value="isCheck") boolean isCheck)
I can get the isCheck boolean value.
But when the code in contoller is:
public void test(TestVO testVO)
TestVO javabean:
public class TestVO {
private boolean isPrecheck;
public boolean isPrecheck() {
return isPrecheck;
}
public void setPrecheck(boolean isPrecheck) {
this.isPrecheck = isPrecheck;
}
}
I can not set the request parameter to this Javabean.
Anyone has ideas?
You can you the PropertiesEditor of the Spring.
http://static.springsource.org/spring/docs/3.2.x/javadoc-api/org/springframework/beans/propertyeditors/CustomBooleanEditor.html
Inside your controller create a method to set the editor
public void initBinder(WebDataBinder binder) {
binder.registerCustomEditor(Boolean.class, new CustomBooleanEditor(allowEmpty???));
}
This is due to boolean naming convention and associated ambiguity with its getter methods.
Rename your boolean from isPrecheck to precheck and it will work.
I have a base request type..
class RequestBase
{
public string inputId;
public string derivedid;
}
and types that inherit ..
class RequestA : RequestBase
{
public string name;
}
and
class RequestB : RequestBase
{
public string color;
}
I have a webapi service, some actions take an input parameter of RequestA, some take RequestB
[HttpPost]
[MyFilter]
[ActionName("Process1")]
public HttpResponseMessage Process1(RequestA request)
{
//do something with request.derivedId
}
[HttpPost]
[MyFilter]
[ActionName("Process2")]
public HttpResponseMessage Process2(RequestB request)
{
//do something with request.derivedId
}
I have an actionfilter that takes the inputId from the request and generates a derivedId
public override void OnActionExecuting(HttpActionContext actionContext)
{
RequestBase request = (RequestBase)actionContext.ActionArguments["request"];
string inputId = request.inputId;
string derivedId = inputId + "123";
// ?? somehow inject derivedId back into the actionContext so that my controller methods can access?
}
As my comment states above, I'd like to populate the derivedId field and have it accessible to my controller methods.
Thanks in advance
There's a few solutions to this problem already described in this thread - one of them should suit you:
ASP.NET MVC Pass object from Custom Action Filter to Action
I am trying to submit a form from Ext JS 4 to a Spring 3 Controller using JSON. I am using Jackson 1.9.8 for the serialization/deserialization using Spring's built-in Jackson JSON support.
I have a status field that is initially null in the Domain object for a new record. When the form is submitted it generates the following json (scaled down to a few fields)
{"id":0,"name":"someName","status":""}
After submitted the following is seen in the server log
"nested exception is org.codehaus.jackson.map.JsonMappingException: Can not construct instance of com.blah.domain.StatusEnum from String value '': value not one of the declared Enum instance names"
So it appears that Jackson is expecting a valid Enum value or no value at all including an empty string. How do I fix this whether it is in Ext JS, Jackson or Spring?
I tried to create my own ObjectMapper such as
public class MyObjectMapper extends Object Mapper {
public MyObjectMapper() {
configure(DeserializationConfig.Feature.ACCEPT_EMPTY_STRING_AS_NULL_OBJECT, true);
}
}
and send this as a property to MappingJacksonMappingView but this didn't work. I also tried sending it in to MappingJacksonHttpMessageConverter but that didn't work. Side question: Which one should I be sending in my own ObjectMapper?
Suggestions?
The other thing you could do is create a specialized deserializer (extends org.codehaus.jackson.map.JsonDeserializer) for your particular enum, that has default values for things that don't match. What I've done is to create an abstract deserializer for enums that takes the class it deserializes, and it speeds this process along when I run into the issue.
public abstract class EnumDeserializer<T extends Enum<T>> extends JsonDeserializer<T> {
private Class<T> enumClass;
public EnumDeserializer(final Class<T> iEnumClass) {
super();
enumClass = iEnumClass;
}
#Override
public T deserialize(final JsonParser jp,
final DeserializationContext ctxt) throws IOException, JsonProcessingException {
final String value = jp.getText();
for (final T enumValue : enumClass.getEnumConstants()) {
if (enumValue.name().equals(value)) {
return enumValue;
}
}
return null;
}
}
That's the generic class, basically just takes an enum class, iterates over the values of the enum and checks the next token to match any name. If they do it returns it otherwise return null;
Then If you have an enum MyEnum you'd make a subclass of EnumDeserializer like this:
public class MyEnumDeserializer extends EnumDeserializer<MyEnum> {
public MyEnumDeserializer() {
super(MyEnum.class);
}
}
Then wherever you declare MyEnum:
#JsonDeserialize(using = MyEnumDeserializer.class)
public enum MyEnum {
...
}
I'm not familiar with Spring, but just in case, it may be easier to handle that on the client side:
Ext.define('My.form.Field', {
extend: 'Ext.form.field.Text',
getSubmitValue: function() {
var me = this,
value;
value = me.getRawValue();
if ( value === '' ) {
return ...;
}
}
});
You can also disallow submitting empty fields by setting their allowBlank property to false.
Ended up adding defaults in the EXT JS Model so there is always a value. Was hoping that I didn't have to this but it's not that big of a deal.
I have the same issue. I am reading a JSON stream with some empty strings. I am not in control of the JSON stream, because it is from a foreign service. And I am always getting the same error message. I tried this here:
mapper.getDeserializationConfig().with(DeserializationConfig.Feature.ACCEPT_EMPTY_STRING_AS_NULL_OBJECT);
But without any effect. Looks like a Bug.