Cloud Application #1 B) Build your own Java Microservice

import java.util.Date;
import java.util.UUID;

public class SampleDBObj
{
    private Date timestamp;
    private String uid;
    private String name;
    private String text;
    private String description;

    public SampleDBObj(String name, String text, String description) {
    	this.timestamp = new Date();
    	this.uid = UUID.randomUUID().toString();
    	this.name = name;
    	this.text = text;
    	this.description = description;

    }
    
    public SampleDBObj(Date timestamp, String uid, String name, String text, String description) {
    	this.timestamp = timestamp;
    	this.uid = uid;
    	this.name = name;
    	this.text = text;
    	this.description = description;

    }

	public String toCSVLine() {
		return this.timestamp + "," + this.uid + "," + this.name + "," + this.text + "," + this.description;
	}

	public Date getTimestamp() {
		return timestamp;
	}

	public String getUid() {
		return uid;
	}

	public String getName() {
		return name;
	}

	public String getText() {
		return text;
	}

	public String getDescription() {
		return description;
	}
	
}

import javax.ws.rs.GET;
import javax.ws.rs.Path;
import javax.ws.rs.Produces;
import javax.ws.rs.QueryParam;
import javax.ws.rs.core.MediaType;

@Path("/")
public class SampleServlet {
	

	// http://localhost:3001/api/v1/someMethod?someParam=name
	@Path("helloWorld")
	@GET //HTTP Method
	@Produces(MediaType.APPLICATION_JSON) // Response Type of the Route (with a REST-API often used e.g. json) 
	public String helloWorld(@QueryParam("someParam") String name) {
		return "My name is: " + name;			
	}	
}

import org.eclipse.jetty.server.Server;
import org.eclipse.jetty.servlet.ServletContextHandler;
import org.eclipse.jetty.servlet.ServletHolder;
import org.glassfish.jersey.servlet.ServletContainer;

public class Service {

	public static void main(String[] args) {
		new Service().startup();
	}

	public boolean startup() {
		ServletContextHandler context = new ServletContextHandler(ServletContextHandler.NO_SESSIONS);
		context.setContextPath("/");
		
		Server server = new Server(3001);
		server.setHandler(context);
		
		ServletHolder servlet = context.addServlet(ServletContainer.class, "/service/*");
		servlet.setInitParameter("jersey.config.server.provider.classnames", SampleServlet.class.getCanonicalName());
		
		try {
			server.start();
			return true;
		} catch (Exception e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		return false;
	}
}

import java.util.HashMap;
import java.util.Map;

import org.eclipse.jetty.server.Server;
import org.eclipse.jetty.servlet.ServletContextHandler;
import org.eclipse.jetty.servlet.ServletHolder;
import org.glassfish.jersey.servlet.ServletContainer;

public class Service {

	public static void main(String[] args) {
		
		new Service().startup();
	}

	public boolean startup() {
		ServletContextHandler context = new ServletContextHandler(ServletContextHandler.NO_SESSIONS);
		context.setContextPath("/");
		
		Server server = new Server(3001);
		server.setHandler(context);
		
		registerServletsV1(context);
		
		try {
			server.start();
			return true;
		} catch (Exception e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		return false;
	}
	
	private void registerServletsV1(ServletContextHandler context) {
		Map<String, Class<?>> mappings = new HashMap<>();
		// name where our servlet is available
		mappings.put("service", SampleServlet.class);
		// api version
		registerServlets(context, "v1", mappings);
	}

	private void registerServlets(ServletContextHandler context, String version,
		Map<String, Class<?>> mappings) {

		for (String key : mappings.keySet()) {
			Class<?> value = mappings.get(key);

			// /api/v1/service/getAll for example
			ServletHolder servlet = context.addServlet(ServletContainer.class, "/api/" + version + "/" + key + "/*");
			servlet.setInitParameter("jersey.config.server.provider.classnames", value.getCanonicalName());
		}
	}
	
}

import java.io.FileInputStream;
import java.io.IOException;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.sql.Timestamp;
import java.util.ArrayList;
import java.util.List;
import java.util.Properties;

public class DBUtils {

	private Connection connection;
	private PreparedStatement preparedStatement;
	
	public DBUtils() {
		Properties prop = new Properties();
		try {
			// load config.properties for db credentials
			prop.load(new FileInputStream("src/main/resources/config.properties"));
			// load jdbc driver and start db connection
			// mit "SET GLOBAL time_zone = "+3:00" time_zone bei mysql setzen um keine TimeZone errors zu bekommen
			Class.forName("com.mysql.cj.jdbc.Driver");
			connection = DriverManager.getConnection("jdbc:mysql://" + prop.getProperty("host", "localhost") +  "/"+prop.getProperty("database"), prop.getProperty("user"), prop.getProperty("password", "lol"));
			String query = "INSERT INTO someTable (timestamp, uid, name, text, description) values (?, ?, ?, ?, ?)";
			// preparedStatement benefits: faster, no sql injection is possible
			// must be created once initially with the query and is then only filled with data; this improves performance.
			preparedStatement = connection.prepareStatement(query);
		} catch (IOException e) {
			e.printStackTrace();
		}
		catch (SQLException e) {
			e.printStackTrace();
		} catch (ClassNotFoundException e) {
			e.printStackTrace();
		}
	}
	
	/**
	 * insert the obj to the database
	 * 
	 * @param SambleDBObj
	 * @throws SQLException
	 */
	public void insert(SampleDBObj obj) throws SQLException {
		preparedStatement.setTimestamp(1, new Timestamp(System.currentTimeMillis()));
		preparedStatement.setString(2, obj.getUid());
		preparedStatement.setString(3, obj.getName());
		preparedStatement.setString(4, obj.getText());
		preparedStatement.setString(5, obj.getDescription());
		preparedStatement.executeUpdate();
	}
	
	/**
	 * 
	 * @return List<SampleDBObj> - return all entrys
	 * @throws SQLException
	 */
	public List<SampleDBObj> getAll() throws SQLException {
		Statement statement = connection.createStatement();
		ResultSet rs = statement.executeQuery("SELECT * FROM someTable");
		List <SampleDBObj> objs = new ArrayList<SampleDBObj>();
		while(rs.next()) {    
			SampleDBObj obj = new SampleDBObj(rs.getDate("timestamp"), rs.getString("uid"), rs.getString("name"), rs.getString("text"), rs.getString("description"));
			objs.add(obj);
		}
		return objs;
	}

	/**
	 * 
	 * @return SampleDBObj - return specific entry by name
	 * @throws SQLException
	 */
	public SampleDBObj getByName(String name) throws SQLException {
		PreparedStatement statement = connection.prepareStatement("SELECT * FROM someTable WHERE name = ?");
		statement.setString(1, name);
		ResultSet rs = statement.executeQuery();
		if(rs.next()) {
			return new SampleDBObj(rs.getDate("timestamp"), rs.getString("uid"), rs.getString("name"), rs.getString("text"), rs.getString("description"));
		}
		return null;
	}
}

import java.lang.reflect.Field;
import java.sql.SQLException;
import java.util.Date;
import java.util.List;

import javax.ws.rs.GET;
import javax.ws.rs.Path;
import javax.ws.rs.Produces;
import javax.ws.rs.QueryParam;
import javax.ws.rs.core.MediaType;
import javax.ws.rs.core.Response;

import org.eclipse.jetty.util.StringUtil;

import com.google.gson.Gson;


@Path("/")
public class SampleServlet {
	
	private DBUtils databaseUils;
	
	public SampleServlet() {
		databaseUils = new DBUtils();
	}

	// http://localhost:3001/api/v1/service/insert
	@Path("insert")
	@GET
	@Produces(MediaType.APPLICATION_JSON)
	public Response insert(
			@QueryParam("name") String name,
			@QueryParam("text") String text,
			@QueryParam("description") String description){

		if(StringUtil.isNotBlank(name) && StringUtil.isNotBlank(text) && StringUtil.isNotBlank(description)) {
			SampleDBObj someObj = new SampleDBObj(name, text, description);
			try {
				databaseUils.insert(someObj);
				return Response.ok("Obj successfully created").build();
			} catch (SQLException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
				return Response.status(404, "An error occurred while calling the service, please try again. \r\n" + e.getMessage()).build();
			}
		} else {
			return Response.status(404, "Object could not be created, one of the required parameters was empty").build();
		}
	}

	
	// http://localhost:3001/api/v1/service/getByName
	@Path("getByName")
	@GET
	@Produces(MediaType.APPLICATION_JSON)
	public String getByName(@QueryParam("name") String name) {
		if(StringUtil.isNotBlank(name)) {
		try {
			return new Gson().toJson(databaseUils.getByName(name));
		} catch (SQLException e) {
			e.printStackTrace();
			return "An error occurred while calling the service, please try again. \r\n" + e.getMessage();
		}
		} else {
			return new Gson().toJson("Object could not be created, one of the required parameters was empty");
		}
	}
	
	// http://localhost:3001/api/v1/service/getAll
	@Path("getAll")
	@GET
	@Produces(MediaType.APPLICATION_JSON)
	public String get() {
		try {
			return new Gson().toJson(databaseUils.getAll());
		} catch (SQLException e) {
			e.printStackTrace();
			return "An error occurred while calling the service, please try again. \r\n" + e.getMessage();
		}
	}
	
	@Path("export")
	@GET
	@Produces(MediaType.APPLICATION_OCTET_STREAM)
	public Response export() {
		try {
			StringBuilder sb = new StringBuilder();
			for(Field field : SampleDBObj.class.getDeclaredFields()) {
				sb.append(field.getName()).append(",");
			}
			// load everything from database
			List<SampleDBObj> objects = databaseUils.getAll();
			//header
			sb.deleteCharAt(sb.length()-1);
			for (SampleDBObj obj : objects) {
				sb.append("\r\n");
				sb.append(obj.toCSVLine());
			}
			return Response.ok(sb.toString()).header("Content-Disposition", "attachment; filename=" + new Date().toString() + "-export-objs.csv").build();
			
		} catch (SQLException e) {
			e.printStackTrace();
			return null;
		}		
	}
}