In Java say I have a class that represents http headers:
public class Headers {
String 'x-requested-by' = "foo";
String 'content-type' = "application/json"
}
because of the field names with non-standard variable names (hyphens), typically a more dynamic map is used like so:
Map<String, String> map = new HashMap<String, String>();
but my quesetion is - is there a way to declare which fields will exist in there statically, instead of only at runtime?
You can use an enum map, which will only accept keys of a specified enum type, while the enum itself will statically limit options.
enum Headers {
X_REQUESTED_BY("x-requested-by"), CONTENT_TYPE("content-type");
private String headerName;
private Headers(String n) {
this.headerName = n;
}
public String getHeaderName() {
return headerName;
}
}
And use the enum map to store values:
Map<Headers, String> headerValues = new EnumMap<>(Headers.class);
Your API can then be extended with such methods as addHeader(Headers h), which makes it possible to statically limit options while keeping it type-safe.
No. Only one thing you can do is init a Map with default values after initialization.
public class Header {
public static final String X_REQUESTED_BY = "x-requested-by";
public static final String CONTENT_TYPE = "content-type";
private final Map<String, String> map = new HashMap<String, String>();
{
map.put(X_REQUESTED_BY, "foo");
map.put(CONTENT_TYPE, "application/json");
}
}
Related
I am trying to create a map from all the attributes that a class have.My class looks like :
public class MyInventory
{
private int tiers = 80;
private int stearing =135;
private int battery = 46;
}
Now I have collected all the methods that the class has as :
Field[] fields = this.getClass().getDeclaredFields();
Now , I am trying to create a Map out of it where keys are the values of the fields and the values are the name of the fields. Example :
Map<46,battery> ...etc
Is there a way to do it?
The attribute values for the above mentioned class were generated by mapping to properties file and by using spring annotation #ConfigurationProperties. Now I need to create the Map but keys the values of the attributes. I tried to use reflect. However did not find a way to get the value of the fields.
Thanks
You can use Introspector class.
public Map<Object, String> populateMap(final Object o) throws Exception {
Map<Object, String> result = new HashMap<>();
for (PropertyDescriptor pd : Introspector.getBeanInfo(o.getClass()).getPropertyDescriptors()) {
String fieldName = pd.getName();
if("class".equals(fieldName) continue;
Object value = pd.getReadMethod().invoke(o);
result.put(value, fieldName);
}
return result;
}
You can call the above method, passing your class as argument.
MyInventory mi = new MyInventory();
// Sets the properties of mi
mi.setXXX...
// Populates map
populateMap(mi);
Map<Integer, String> map() throws IllegalArgumentException, IllegalAccessException {
Field[] fields = getClass().getDeclaredFields();
Map<Integer,String> map = new HashMap<>();
for (Field field : fields) {
map.put(field.getInt(this), field.getName());
}
return map;
}
Of course it will not map properly if different fields have the same value.
I think, you can have getter method in your class
public class MyInventory
{
private int tiers = 80;
private int stearing =135;
private int battery = 46;
public int getBattery()
{
return battery;
}
//and other getter
}
and then you can populate your map as
map.put(inventory.getBattery(),"battery");
Because, when you have value, which means you know what is the type for which you are populating map.
You can use json parser. For example jackson:
import com.fasterxml.jackson.databind.ObjectMapper;
...
ObjectMapper mapper = new ObjectMapper();
return mapper.readValue(mapper.writeValueAsString(fooOject), HashMap.class);
Is it possible to convert map into a pojo when attribute names are different?
I am extracting raw input into a map to have the following data. Data can vary based on message type. For example:
for Message type = STANDARD
Map<String, Double> data = new HashMap<>();
data.set('TEMP', 18.33);
data.set('BTNUM', 123);
for Message type = NON_STANDARD
Map<String, Double> data = new HashMap<>();
data.set('GPSLAT', 12.33);
data.set('GPSLON', 42.33);
For each message type I have a Java model class
#Data
public class StandardMessage {
private String longitude;
private String latitude;
}
#Data
public class NonStandardMessage {
private String temperature;
private String btNumber;
}
Currenly I am mapping data to POJO class manually like below
StandardMessage sm = new StandardMessage();
sm.setLongitude(data.get('GPSLON'));
NonStandardMessage nsm = new NonStandardMessage();
nsm.setTemperature(data.get('TEMP'));
Is it possible to make above mapping generic? i.e setting object property without knowing name?
In Typescript we can achieve this easily by defining configuration like:
objectPropertyMapping = new Map();
objectPropertyMapping.set('GPSLAT', 'latitude');
objectPropertyMapping.set('GPSLON', 'longitude');
standardMessage = {};
data.forEach((value: boolean, key: string) => {
standardMessage[ObjectPropertyMapping.get(key)] = data[key];
});
https://stackblitz.com/edit/angular-zjn1kc?file=src%2Fapp%2Fapp.component.ts
I know Java is a statically-typed language, just wondering is there a way to achieve this like typescript or we have to map manually all the time?
We use jackson-databind. It uses annotations for configuration.
Here are some example:
The entity class:
class MessageRequest {
#JsonProperty("A")
private String title;
#JsonProperty("B")
private String body;
... getters and setters ...
}
The main method:
public static void main(String[] args) {
ObjectMapper objectMapper = new ObjectMapper();
Map<String, Object> source = new HashMap<>();
source.put("A", "This is the title");
source.put("B", "Here is the body");
MessageRequest req = objectMapper.convertValue(source, MessageRequest.class);
System.out.println(req.getTitle());
System.out.println(req.getBody());
}
When reading a JSON file, i would like to map my class as follows:
public class Effect {
private final String type;
private final Map<String, String> parameters;
public Effect(String type, Map<String, String> parameters) {
this.type = type;
this.parameters = parameters;
}
public String getType() {
return this.type;
}
public Map<String, String> getParameters() {
return this.parameters;
}
}
{
"type": {
"key1": "value1",
"key2": "value2",
}
}
So, the mapped JSON object consists of type as the only key and parameters as its value.
I would like to use #JsonCreator on the constructor, but can't figure out, how to map the fields. Do i need to write a custom deserializer or is there an easier way to map the class like i want?
I wrote a custom deserializer, which does what i want, but there might be an easier way, maybe with annotations alone, which i would like to know:
public class EffectDeserializer extends StdDeserializer<Effect> {
private static final long serialVersionUID = 1L;
public EffectDeserializer() {
super(Effect.class);
}
#Override
public Effect deserialize(JsonParser parser, DeserializationContext context) throws IOException, JsonProcessingException {
JsonNode node = parser.getCodec().readTree(parser);
Iterator<String> fieldNames = node.fieldNames();
if(fieldNames.hasNext()) {
String type = fieldNames.next();
Map<String, String> parameters = new HashMap<>();
for(Iterator<Entry<String, JsonNode>> fields = node.get(type).fields(); fields.hasNext(); ) {
Entry<String, JsonNode> field = fields.next();
parameters.put(field.getKey(), field.getValue().textValue());
}
return new Effect(type, parameters);
}
return null;
}
}
Another way i found would be adding a JsonCreator (constructor in this case), that takes a Map.Entry<String, Map<String, String> and uses that to initialize the values, like this:
#JsonCreator
public Effect(Map.Entry<String, Map<String, String>> entry) {
this.type = entry.getKey();
this.parameters = entry.getValue();
}
If there's no way to get it done with a "normal" constructor, i will probably end up using this, as it uses Jackson's default mapping for Map.Entry, reducing possible error margin.
Add a static factory method that accepts a Map with a dynamic key:
#JsonCreator
public static Effect create(Map<String, Map<String, String>> map) {
String type = map.keySet().iterator().next();
return new Effect(type, map.get(type));
}
EDIT: Just noticed this is basically an uglier version of your own solution using Map.Entry. I would go with that instead.
Is there a Java standalone implementation to extract values of parameters in an URI as defined by an URI-Template (RFC 6570)?
The best implementation I've found is a ruby implementation ( https://github.com/sporkmonger/addressable )
Via http://code.google.com/p/uri-templates/wiki/Implementations I found a Java implementation: Handy-URI-Templates
It supports the resolution of an URI-Template with parameter values to a final URI. Unfortunately, it can not do the reverse: extraction of parameter values in the URI according URI-Template.
Implentations of the JAX-RS (or Restlet) have this feature internally.
But none seems to have isolated this feature module which could used independently.
Does anyone have another idea?
Here a example to Use spring-Web :
import org.springframework.web.util.UriTemplate;
public class UriParserSpringImpl implements UriParser {
private final UriTemplate uriTemplate;
private final String uriTemplateStr;
public UriParserSpringImpl(final String template) {
this.uriTemplateStr = template;
this.uriTemplate = new UriTemplate(template);
}
#Override
public Map<String, String> parse(final String uri) {
final boolean match = this.uriTemplate.matches(uri);
if (!match) {
return null;
}
return uriUtils.decodeParams(this.uriTemplate.match(uri));
}
#Override
public Set<String> getVariables() {
return Collections.unmodifiableSet(new LinkedHashSet<String>(this.uriTemplate.getVariableNames()));
}
}
Another for Jersey (JAX-RS implementation) :
import com.sun.jersey.api.uri.UriTemplate;
public class UriParserJerseyImpl implements UriParser {
private final UriTemplate uriTemplate;
private final Map<String, String> valuesMaps;
public UriParserJerseyImpl(final String template) {
this.uriTemplate = new UriTemplate(template);
final Map<String, String> valuesMaps = new HashMap<String, String>();
for (final String prop : this.uriTemplate.getTemplateVariables()) {
valuesMaps.put(prop, null);
}
this.valuesMaps = Collections.unmodifiableMap(valuesMaps);
}
#Override
public Map<String, String> parse(final String uri) {
final Map<String, String> values = new HashMap<String, String>(this.valuesMaps);
final boolean match = this.uriTemplate.match(uri, values);
if (!match) {
return null;
}
return values;
}
#Override
public Set<String> getVariables() {
return this.valuesMaps.keySet();
}
}
With interface :
public interface UriParser {
public Set<String> getVariables();
public Map<String, String> parse(final String uri);
}
The damnhandy uri template library has an open issue for exactly this feature. I've already gotten the PR for the feature merged and it should be out in version 2.2! Head over there and let the maintainers know you're interested.
Also if you can't wait, you can see how I did it here and use that for yourself.
java.net.URI
Can't set the parameters after it's instantiated, but it has a nice set of getters and you can contruct a new one to alter it.
Here is my problem:
I have list of possible Product categories(for example: Shoes,Mode,Women), and I need to convert this to my specific names.
example: I get the category Women and I need to convert this to Lady's.
I have about 40 category names that i need to convert.
My question is :What is the best way to do this in JAVA.
I thought about switch case, but i dont know is this a good solution.
switch (oldCategoryName) {
case "Women":
return "Ladys";
default:
return "Default";
}
You can use static map for that.
Make a Static Map as below
public class PropertiesUtil {
private static final Map<String, String> myMap;
static {
Map<String, String> aMap = new HashMap<String, String>();
aMap.put("Women", "Ladys");
aMap.put("another", "anotherprop");
myMap = Collections.unmodifiableMap(aMap);
}
}
then get the replacing string..
String womenReplace = PropertiesUtil.myMap.get("Women");
You can also consider using enums:
public enum ProductsCategory {
Mode("MyMode"),
Shoes("MyShoes");
private String name;
private ProductsCategory(String name) {
this.name = name;
}
public String getName() {
return name;
}
}
Then the retrieval:
String myModeStr = ProductsCategory.Mode.getName();
Note that the java switch does not work on String objects for java versions below 7.
You can store values in a map :
// storing
Map<String, String> map = new HashMap<String, String>();
map.put("Women", "Ladys");
// add other values
// retrieving
String ladys = map.get("Women");
Or you can also use a .properties file to store all those associations, and retrieve a property object.
InputStream in = new FileInputStream(new File("mapping.properties"));
Properties props = new Properties();
props.load(in);
in.close();
String ladys = props.getProperty("Women");