jStrainer

A simple filter chaining mechanism for java objects

A common problem when receiving data from forms, legacy databases or third party services, is the necessity of to filter, sanitize and format this data before it can be processed. This kind of work turns out to be repetitive, leaving the code complex with many unnecessary lines. Having this situation present in the dayly of many programmers, this project aims to solve these problems.

Demo

Demo repository: https://github.com/jstrainer/jstrainer-demo

Requirements

Java 1.8 or later

Maven

<dependencies>
    <dependency>
        <groupId>com.github.jstrainer</groupId>
        <artifactId>jstrainer</artifactId>
        <version>1.0.0</version>
    </dependency>
</dependencies>

General Usage

1. Defining the object

package demo;

import com.github.jstrainer.Filtered;
import com.github.jstrainer.filter.Alphanum;
import com.github.jstrainer.filter.Numeric;
import com.github.jstrainer.filter.StripTags;
import com.github.jstrainer.filter.ToUpperCase;
import com.github.jstrainer.filter.Trim;

public class Person {

    @Trim
    @StripTags
    private String name;

    @Filtered
    private Address address;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Address getAddress() {
        return address;
    }

    public void setAddress(Address address) {
        this.address = address;
    }

    @Override
    public String toString() {
        return "Person [name=" + name + ", address=" + address + "]";
    }

}

class Address {

    @Numeric
    private String postcode;

    @Alphanum(allowSpace = true)
    private String streetName;

    private String buildingNumber;

    private String city;

    @Trim
    private String stateOrRegion;

    @ToUpperCase
    private String country;

    // getters and setters...

    @Override
    public String toString() {
        return "Address [postcode=" + postcode + ", streetName=" + streetName + ", buildingNumber=" + buildingNumber
                + ", city=" + city + ", stateOrRegion=" + stateOrRegion + ", country=" + country + "]";
    }

}

Annotations used in the example:

• @Trim - Remove whitespace from both ends of a string
• @Filtered - Apply filters to child object
• Other filters

2. Filter the object

Address address = new Address();
address.setStreetName("*C!o#untry &Street/");
address.setCity("Poughkeepsie");
address.setCountry("usa");
address.setStateOrRegion(" NY ");
address.setPostcode("12603A");
address.setBuildingNumber("539");
    
Person person = new Person();
person.setName("<b>Leonardo</b>           ");
person.setAddress(address);

Strainer strainer = new Strainer();
strainer.filter(person);

System.out.println(person);
    
    /* printed
    Person [
        name=Leonardo, 
        address=Address [
            postcode=12603, 
            streetName=Country Street, 
            buildingNumber=539, 
            city=Poughkeepsie, 
            stateOrRegion=NY, 
            country=USA
        ]
    ] */

Available Filters

Filter	Parameters	Property Type	Description
@Alpha	allowSpace, allowAccents	String	Returns only letters
@Alphanum	allowSpace, allowNewline	String	Returns only letters and numbers
@Blacklist	list	String	Returns null if the value is present in the list
@DefaultValue	value	String	Returns a default value if value is null
@LeftPad	length, padChar	String	Appends zeros (or other character) to the left
@Numeric		String	Returns only numbers
@Prefix	value, ifNotPresent	String	Adds a prefix to a String
@Replace	search, replacement, all, ignoreCase	String	Replaces the first or all occurrences of the search with the replacement
@RightPad	length, padChar	String	Appends zeros (or other character) to the right
@Round	scale	Double	Rounds a Double
@RoundDown	scale	Double	Rounds a Double down
@RoundUp	scale	Double	Rounds a Double up
@StripNewlines		String	Removes all new line characters
@StripTags		String	Removes all tags
@Suffix	value, ifNotPresent	String	Adds a suffix to a String
@ToLowerCase		String	Converts a String to lower case
@ToUpperCase		String	Converts a String to upper case
@Trim	stripChar	String	Removes leading and trailing whitespace (or other character)
@Whitelist	list	String	Returns null if the value is not present in the list

Creating a custom Filter

1. Add a new @interface to define the filter annotation

package demo;

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

import com.github.jstrainer.FilteredBy;

@Documented
@FilteredBy(ReverseFilter.class) // the class that will filter the data
@Target({ ElementType.METHOD, ElementType.FIELD })
@Retention(RetentionPolicy.RUNTIME)
public @interface Reverse {

}

2. Implement the filter

package demo;

import com.github.jstrainer.filter.Filter;

public class ReverseFilter implements Filter<Reverse, String> {

    @Override
    public String filter(String value, Reverse annotation) {
        if (value == null) {
            return value;
        }

        return new StringBuffer(value).reverse().toString();
    }

}

3. Using the new filter annotation

@Reverse
private String reversed;