Apache Commons CSV makes read and write files funtionality easy whether is Comma or Tab Separated (CSV), for more information go here. This time we will review how to write/read CSV tab delimeted files in java. Let’s create a Java basic project structure using lazybones.
lazybones create java-basic csv-apache-commons
Previous command will create this structure
<proj>
|
+- src
|
+- main
| |
| +- java
|
+- test
| |
| +- java
Edit your build.gradle file in order to create a Jar task builder plus adding Apache commons and Junit 5 dependencies.
ext {
springVersion = '5.2.2.RELEASE'
apacheCSVVersion = '1.7'
junitJupiterVersion = '5.5.2'
}
apply plugin: "java"
apply plugin: "application"
version = '1.0.0'
task buildJar(type: Jar) {
manifest {
attributes 'Implementation-Title': 'Transforming an Excel file using AWS Lambda',
'Implementation-Version': version,
'Main-Class': 'example.Application'
}
baseName = project.name + '-all'
from { configurations.compile.collect { it.isDirectory() ? it : zipTree(it) } }
with jar
}
repositories {
mavenCentral()
}
dependencies {
implementation "org.springframework:spring-context:$springVersion"
implementation "org.springframework:spring-core:$springVersion"
implementation "org.apache.commons:commons-csv:$apacheCSVVersion"
testImplementation "org.junit.jupiter:junit-jupiter-api:$junitJupiterVersion"
testRuntime "org.junit.jupiter:junit-jupiter-engine:$junitJupiterVersion"
}
test {
useJUnitPlatform()
}
Now is time to create a CSV file reader under project-dir/src/main/java/example/
package example;
import java.io.FileReader;
import java.io.IOException;
import java.util.List;
import java.util.ArrayList;
import org.apache.commons.csv.CSVFormat;
import org.apache.commons.csv.CSVRecord;
public class CsvFileReader {
public List<List<String>> read(String path){
List elements = new ArrayList<List<String>>();
try{
FileReader input = new FileReader(path);
Iterable<CSVRecord> records = CSVFormat.TDF.withHeader("id", "name", "email").parse(input);
records.forEach(record -> {
List<String> row = new ArrayList<String>();
row.add(record.get("id"));
row.add(record.get("name"));
row.add(record.get("email"));
elements.add(row);
});
} catch(IOException ioe){
throw new CsvException(ioe.getMessage());
}
return elements;
}
}
CsvFileReader reads our CSV file using CSVFormat.TDF.withHeader("id", "name", "email").parse(input) where:
TDFis tab delimited specificationparseaction reads fromFileReaderinput
This is the CsvException
package example;
import java.lang.RuntimeException;
public class CsvException extends RuntimeException {
CsvException(String message){
super(message);
}
}
And this is the CSV example file:
id name email
1 eric erich@email.com
2 martin martinv@email.com
3 josdem josdem@email.com
For reading our the CSV file, we need to create this simple POJO containing target id, name and email.
package example;
public class Target {
private String id;
private String name;
private String email;
public Target(String id, String name, String email) {
this.id = id;
this.name = name;
this.email = email;
}
public void setId(String id) {
this.id = id;
}
public String getId() {
return id;
}
public void setName(String name) {
this.name = name;
}
public String getName() {
return name;
}
public void setEmail(String email) {
this.email = email;
}
public String getEmail() {
return email;
}
}
CsvFileWriter writes the CSV file using CSVFormat.TDF.withHeader("id", "name", "email").withRecordSeparator(NEW_LINE_SEPARATOR).print(output) where:
- TDF is tab delimited specification
withRecordSeparatorspecify an ‘\n’ character at the ending of new record writtenprintaction writes to the FileWriter output
package example;
import java.io.FileWriter;
import java.io.IOException;
import java.util.List;
import java.util.ArrayList;
import org.apache.commons.csv.CSVFormat;
import org.apache.commons.csv.CSVRecord;
import org.apache.commons.csv.CSVPrinter;
public class CsvFileWriter {
private static final String NEW_LINE_SEPARATOR = "\n";
public void write(List<Target> targets, String path) {
List elements = new ArrayList<List<String>>();
try {
FileWriter output = new FileWriter(path);
CSVPrinter printer = CSVFormat.TDF.withHeader("id", "name", "email")
.withRecordSeparator(NEW_LINE_SEPARATOR).print(output);
for (Target target : targets) {
List<String> record = new ArrayList<String>();
record.add(target.getId());
record.add(target.getName());
record.add(target.getEmail());
printer.printRecord(record);
}
output.flush();
output.close();
} catch (IOException ioe) {
throw new CsvException(ioe.getMessage());
}
}
}
This are our test cases written in Junit 5
package example;
import static org.junit.jupiter.api.Assertions.assertAll;
import static org.junit.jupiter.api.Assertions.assertTrue;
import static org.junit.jupiter.api.Assertions.assertEquals;
import java.util.List;
import java.util.Arrays;
import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.DisplayName;
class CsvFileReaderTest {
private CsvFileReader reader = new CsvFileReader();
@Test
@DisplayName("Should read csv file")
void shouldReadCsvFile(){
String path = "src/test/resources/csv.txt";
List<List<String>> result = reader.read(path);
assertAll("rows",
() -> assertEquals(4, result.size(), "should have four rows"),
() -> assertTrue(result.contains(Arrays.asList("id","name","email")), "should have header"),
() -> assertTrue(result.contains(Arrays.asList("1","eric","erich@email.com")), "should contain Eric"),
() -> assertTrue(result.contains(Arrays.asList("2","martin","martinv@email.com")), "should contain Martin"),
() -> assertTrue(result.contains(Arrays.asList("3","josdem","josdem@email.com")), "should contain josdem")
);
}
}
And
package example;
import static org.junit.jupiter.api.Assertions.assertAll;
import static org.junit.jupiter.api.Assertions.assertTrue;
import static org.junit.jupiter.api.Assertions.assertEquals;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.List;
import java.util.Arrays;
import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.DisplayName;
class CsvFileWriterTest {
private CsvFileWriter writer = new CsvFileWriter();
@Test
@DisplayName("Should write csv file")
void shouldWriteCsvFile() throws Exception {
String path = "src/test/resources/csv.txt";
Target t1 = new Target("1", "eric", "erich@email.com");
Target t2 = new Target("2", "martin", "martinv@email.com");
Target t3 = new Target("3", "josdem", "josdem@email.com");
List<Target> targets = Arrays.asList(t1, t2, t3);
writer.write(targets, path);
Files.lines(Paths.get(path)).forEach(line ->
assertTrue(line.contains("email"), "should contains email word")
);
}
}
To run the project:
gradle test
To browse the project go here, to download the project:
git clone git@github.com:josdem/java-workshop.git
cd aws-csv-transformer