POJOs2CSV

Simple and lightweight library that convert POJO collections (lists and sets) into CSV (Comma Separated Values) strings and files.

This is specially useful when you get a POJO collection like a list of entities from an ORM and you want to obtain a CSV representation of that entities (to generate spreesheet reports for example).

Features

• It generates RFC4180 compliant CSV.
• CSV headers can be configured using annotations.
• You can hide columns (fields of the object type elements in the collection) using annotations.
• Optimized for large collections.

Usage

Download pojos2csv-1.0.0.jar and put it in your project classpath.

If you want to build the latest jar version by yourself, you need to install maven, clone this repository and execute:

mvn package (inside the repository directory)

This will buid the project generating the jar file in [REPOSITORY_DIR]/target/collection2csv-x.x.x.jar

Transform a POJO collection into a CSV String

To transform a POJO collection (any object that implement a subinterface of java.util.Collection like java.util.List or java.util.Set) into a CSV String, use the convertToCsvString() method:

String csv = POJOs2CSV.convertToCsvString(yourcollection);

Example

Consider the following class:

public class User {
    private Long id;
    private String name;
    private String lastName;

    public User(Long id, String name, String lastName) {
        this.id = id;
        this.name = name;
        this.lastName = lastName;
    }

    // Getters, Setters and maybe others methods goes here
    ...
}

and the userList ArrayList, an implementation of java.util.List (a subinterface of java.util.Collection) of Users:

List<User> users = new ArrayList<User>();
users.add(new User(1L, "Andrey", "Kolmogorov"));
users.add(new User(2L, "Évariste", "Galois"));
users.add(new User(3L, "David", "Hilbert"));

Then, if you use the convertToCsvString method like this:

String csv = POJOs2CSV.convertToCsvString(usersList);

You will get the following CSV String:

"id","name","lastName"
"1","Andrey","Kolmogorov"
"2","Évariste","Galois"
"3","David","Hilbert"

Important: The collection must not be empty (it will throw a NoSuchElementException), because there is no way to know the type of objects in the collection at runtime (i.e. using reflection) if the collection doesn't contains at least one element.

But If you know the type of objects in the collection, then you can use the method:

POJOs2CSV.convertToCsvString(yourcollection, YourObjectsType.class);

For example:

List<User> users = new ArrayList<User>();
String csv = POJOs2CSV.convertToCsvString(users, User.class);

And then, even if your POJOs collection is empty, it will generate a CSV String containing the CSV Headers.

Writing to a file

You can use the appendCsv method to write into a File:

 Writer writer = new FileWriter("example.csv");
 POJOs2CSV.appendCsv(userList, writer);
 writer.close();

You can also use the appendCsv method to append the generated CSV into any Object that implements the Appendable interface (like FileWriter, PrintStream, PrintWriter, BufferedWriter, etc).

Changing the CSV headers

Sometimes, you want to change the CSV headers to more explicit values, for that purpose you can use the @CSVField annotation.

So, if we add the following annotations to the fields in the User class from the previous example:

public class User {
    private Long id;

    @CSVField(name = "Name")
    private String name;

    @CSVField(name = "Last Name")
    private String lastName;

    public User(Long id, String name, String lastName) {
        this.id = id;
        this.name = name;
        this.lastName = lastName;
    }

    // Getters, Setters and maybe others methods goes here
    ...
}

Then POJOs2CSV.convertToCsvString(users) will return this CSV string:

"id","Name","Last Name"
"1","Andrey","Kolmogorov"
"2","Évariste","Galois"
"3","David","Hilbert"

Hiding class fields (CSV Columns)

Sometimes you want to generate CSV strings without taking account some class fields, you can do this using the annotation @CSVField(ignore = true) to tell convertToString method to "ignore" that field.

So in the previous example if we add the @CSVField(ignore = true) annotation to the id field in the User class:

public class User {
    @CSVField(ignore = true)
    private Long id;

    @CSVField(name = "Name")
    private String name;

    @CSVField(name = "Last Name")
    private String lastName;

    public User(Long id, String name, String lastName) {
        this.id = id;
        this.name = name;
        this.lastName = lastName;
    }

    // Getters, Setters and maybe others methods goes here
    ...
}

Then POJOs2CSV.convertToCsvString(users) will return this CSV string:

"Name","Last Name"
"Andrey","Kolmogorov"
"Évariste","Galois"
"David","Hilbert"

Limitations

• Currently it doesn't work with inheritance, i.e. if the type of objects in your collection extends from another class, the generated CSV String will not include the superclass fields (In future versions it will be supported).

Credits

• Miguel Ángel Carrasco Wens (tlacaelel.software@gmail.com) (original author).

License

Copyright 2013 Miguel Ángel Carrasco Wens (tlacaelel.software@gmail.com)

Released under the MIT License.