Definations And Use :- Annotations

Annotation is Metadata. Metadata is data about data

public class AnnotationsSample {

    protected void execute() {
        Car car = new Car("Ford", "F150", "2018");
        JsonSerializer serializer = new JsonSerializer();
        try {
            serializer.serialize(car);
        } catch (JsonSerializeException e) {
            e.printStackTrace();
        }
    }
}

public class AnnotationsSample {

protected void execute() {

Car car = new Car("Ford", "F150", "2018");

JsonSerializer serializer = new JsonSerializer();

try {

serializer.serialize(car);

} catch (JsonSerializeException e) {

e.printStackTrace();

}

public class Car {
    @JsonField("manufacturer")
    private final String make;
    @JsonField
    private final String model;
    @IgnoreMe
    private final String year;
    public Car(String make, String model, String year) {
        this.make = make;
        this.model = model;
        this.year = year;
    }
    public String getMake() {
        return make;
    }
    public String getModel() {
        return model;
    }
    public String getYear() {
        return year;
    }
    @Override
    public String toString() {
        return year + " " + make + " " + model;
    }
}

public class Car {

@JsonField("manufacturer")

private final String make;

@JsonField

private final String model;

@IgnoreMe

private final String year;

public Car(String make, String model, String year) {

this.make = make;

this.model = model;

this.year = year;

}

public String getMake() {

return make;

}

public String getModel() {

return model;

}

public String getYear() {

return year;

}

@Override

public String toString() {

return year + " " + make + " " + model;

}

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.FIELD)
public @interface IgnoreMe {
    String value() default "";
}

import java.lang.annotation.ElementType;

import java.lang.annotation.Retention;

import java.lang.annotation.RetentionPolicy;

import java.lang.annotation.Target;

@Retention(RetentionPolicy.RUNTIME)

@Target(ElementType.FIELD)

public @interface IgnoreMe {

String value() default "";

}

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.FIELD)
public @interface JsonField {
    String value() default "";
}

import java.lang.annotation.ElementType;

import java.lang.annotation.Retention;

import java.lang.annotation.RetentionPolicy;

import java.lang.annotation.Target;

@Retention(RetentionPolicy.RUNTIME)

@Target(ElementType.FIELD)

public @interface JsonField {

String value() default "";

}

public class JsonSerializeException extends Exception {
    private static final long serialVersionUID = -8845242379503538623L;

    public JsonSerializeException(String message) {
        super(message);
    }
}

public class JsonSerializeException extends Exception {

private static final long serialVersionUID = -8845242379503538623L;

public JsonSerializeException(String message) {

super(message);

}

import java.lang.reflect.Field;
import java.util.HashMap;
import java.util.Map;



public class JsonSerializer {
    private static String getSerializedKey(Field field) {
        String annotationValue = field.getAnnotation(JsonField.class).value();
        if (annotationValue.isEmpty()) {
            return field.getName();
        } else {
            return annotationValue;
        }
    }

    public String serialize(Object object) throws JsonSerializeException {
        try {
            Class<?> objectClass = requireNonNull(object).getClass();
            Map<String, String> jsonElements = new HashMap<>();
            for (Field field : objectClass.getDeclaredFields()) {

                field.setAccessible(true);
                if (field.isAnnotationPresent(JsonField.class)) {
                    jsonElements.put(getSerializedKey(field), (String) field.get(object));
                } else if (field.isAnnotationPresent(IgnoreMe.class)) {

                } else {
                    jsonElements.put(field.getName(), (String) field.get(object));
                }
            }
            System.out.println(toJsonString(jsonElements));
            return toJsonString(jsonElements);
        } catch (IllegalAccessException e) {
            throw new JsonSerializeException(e.getMessage());
        }
    }

    private Object requireNonNull(Object object) {
        if (object == null) {
            throw new NullPointerException();
        } else {
            return object;
        }

    }

    private String toJsonString(Map<String, String> jsonMap) {


        StringBuilder elementsString = new StringBuilder();
        for (Map.Entry<String, String> entry : jsonMap.entrySet())
            elementsString.append("\"").append(entry.getKey()).append("\":\"").append(entry.getValue()).append("\"");
        return "{" + elementsString + "}";
    }
}

import java.lang.reflect.Field;

import java.util.HashMap;

import java.util.Map;

public class JsonSerializer {

private static String getSerializedKey(Field field) {

String annotationValue = field.getAnnotation(JsonField.class).value();

if (annotationValue.isEmpty()) {

return field.getName();

} else {

return annotationValue;

}

public String serialize(Object object) throws JsonSerializeException {

try {

Class<?> objectClass = requireNonNull(object).getClass();

Map<String, String> jsonElements = new HashMap<>();

for (Field field : objectClass.getDeclaredFields()) {

field.setAccessible(true);

if (field.isAnnotationPresent(JsonField.class)) {

jsonElements.put(getSerializedKey(field), (String) field.get(object));

} else if (field.isAnnotationPresent(IgnoreMe.class)) {

} else {

jsonElements.put(field.getName(), (String) field.get(object));

}

System.out.println(toJsonString(jsonElements));

return toJsonString(jsonElements);

} catch (IllegalAccessException e) {

throw new JsonSerializeException(e.getMessage());

}

private Object requireNonNull(Object object) {

if (object == null) {

throw new NullPointerException();

} else {

return object;

}

private String toJsonString(Map<String, String> jsonMap) {

StringBuilder elementsString = new StringBuilder();

for (Map.Entry<String, String> entry : jsonMap.entrySet())

elementsString.append("\"").append(entry.getKey()).append("\":\"").append(entry.getValue()).append("\"");

return "{" + elementsString + "}";

}

shubham sharma September 11, 2018 Read More

Change query string in JAVA

import java.io.UnsupportedEncodingException;
import java.net.MalformedURLException;
import java.net.URLEncoder;
import java.util.HashMap;
import java.util.Map;

public class MyURLClass {
    public String addOrChangeQuery(String mainUrl, String key, String newValue) throws MalformedURLException, UnsupportedEncodingException {
        int queryStart = mainUrl.indexOf('?');
        String newUrl;
        if (queryStart == -1) {
            newUrl = mainUrl + "?" + getNewQuery(null, key, newValue);
        } else {
            newUrl = mainUrl.substring(0, queryStart) + "?" + getNewQuery(mainUrl.substring(queryStart + 1), key, newValue);
        }
        return newUrl;
    }

    private String getNewQuery(String query, String key, String newValue) throws UnsupportedEncodingException {
        Map&lt;String, String&gt; map = new HashMap&lt;&gt;();
        if (query == null) {
            map.put(key, newValue);
        } else {
            String[] params = query.split("&amp;");
            Boolean isKey = false;
            for (String param : params) {
                String queryName = param.split("=")[0];
                String queryValue = param.split("=")[1];
                if (queryName.equalsIgnoreCase(key)) {
                    isKey = true;
                    queryValue = newValue;
                }
                map.put(queryName, queryValue);
            }
            if (!isKey) {
                map.put(key, newValue);
            }
        }
        StringBuilder sb = new StringBuilder();
        for (HashMap.Entry&lt;String, String&gt; e : map.entrySet()) {
            if (sb.length() &gt; 0) {
                sb.append('&amp;');
            }
            sb.append(URLEncoder.encode(e.getKey(), "UTF-8")).append('=').append(URLEncoder.encode(e.getValue(), "UTF-8"));
        }
        return sb.toString();
    }

    private Map&lt;String, String&gt; getQueryMap(String query) {
        Map&lt;String, String&gt; map = new HashMap&lt;&gt;();
        String[] params = query.split("&amp;");
        for (String param : params) {
            String queryName = param.split("=")[0];
            String queryValue = param.split("=")[1];
            map.put(queryName, queryValue);
        }
        return map;
    }
}

import java.io.UnsupportedEncodingException;

import java.net.MalformedURLException;

import java.net.URLEncoder;

import java.util.HashMap;

import java.util.Map;

public class MyURLClass {

public String addOrChangeQuery(String mainUrl, String key, String newValue) throws MalformedURLException, UnsupportedEncodingException {

int queryStart = mainUrl.indexOf('?');

String newUrl;

if (queryStart == -1) {

newUrl = mainUrl + "?" + getNewQuery(null, key, newValue);

} else {

newUrl = mainUrl.substring(0, queryStart) + "?" + getNewQuery(mainUrl.substring(queryStart + 1), key, newValue);

}

return newUrl;

}

private String getNewQuery(String query, String key, String newValue) throws UnsupportedEncodingException {

Map<String, String> map = new HashMap<>();

if (query == null) {

map.put(key, newValue);

} else {

String[] params = query.split("&");

Boolean isKey = false;

for (String param : params) {

String queryName = param.split("=")[0];

String queryValue = param.split("=")[1];

if (queryName.equalsIgnoreCase(key)) {

isKey = true;

queryValue = newValue;

}

map.put(queryName, queryValue);

}

if (!isKey) {

map.put(key, newValue);

}

StringBuilder sb = new StringBuilder();

for (HashMap.Entry<String, String> e : map.entrySet()) {

if (sb.length() > 0) {

sb.append('&');

}

sb.append(URLEncoder.encode(e.getKey(), "UTF-8")).append('=').append(URLEncoder.encode(e.getValue(), "UTF-8"));

}

return sb.toString();

}

private Map<String, String> getQueryMap(String query) {

Map<String, String> map = new HashMap<>();

String[] params = query.split("&");

for (String param : params) {

String queryName = param.split("=")[0];

String queryValue = param.split("=")[1];

map.put(queryName, queryValue);

}

return map;

}

shubham sharma March 17, 2017 Read More

New Dev Point

Some problems explained

JAVA

Definations And Use :- Annotations

Change query string in JAVA