Java & Local Databases

Question

TL DR; Want some Java help with connecting to a truly local database ( no access to server tech ), or if you can whip up code, that will work. All it has to do is query the

Answer 1

Ok, so you need to serve JSON from a local database, right?

You don't need a server, you can serve web pages directly from your local machine ( you just have to point to localhost )

So, basically ( and I know this won't be complete, but I hope is a good start )

You have to:

• Install a servlet container ( Tomcat or Jetty ), they are very easy to use.
• Create a servlet or JSP page to display the data ( JSP are also easy )
• Create a connection using JDBC to a local database such as Derby
• Use a library to transform your data into JSON

Install tomcat

( I will describe for UNIX, but it's the same for Windows)

Download it from here and then unzip the file in some directory you like ( eg. /home/you/ or C:\Users\you\ )

Open a terminal and go to the tomcat bin directory and type catalina.sh run that will start tomcat, you need to have Java installed on your system

Open your browser in http://localhost:8080

It should look like this:

Create a JSP file

Next, go to the tomcat webapps directory, it should contain these folders:

ROOT/
docs/
examples/
host-manager/
manager/

Create a new one, for instance your or whatever and inside create a file Hello.jsp with the following:

Hello.jsp
----------
Hello, world

And then open in your browser: http://localhost:8080/your/Hello.jsp

Should look like:

Create a JDBC program

Next, in your webapp your create the directory: WEB-INF/lib and save there the derby JDBC driver, you can get it from here

Modify your Hello.jsp file to create a sample table like this:

<%@page import="java.sql.*, java.util.*"%>
<%!
     public String getData() {
         List list = new ArrayList();
         try {
             Class.forName("org.apache.derby.jdbc.EmbeddedDriver");
             Connection connection = DriverManager.getConnection("jdbc:derby:yourdb;create=true");
             // The first time:
             PreparedStatement pstmt = connection.prepareStatement(
                 "CREATE TABLE PEOPLE\n"+
                 "(PERSON_ID INT NOT NULL GENERATED ALWAYS AS IDENTITY\n"+
                 "    CONSTRAINT PEOPLE_PK PRIMARY KEY, PERSON VARCHAR(26))");
            pstmt.executeUpdate();
            pstmt = connection.prepareStatement("INSERT INTO PEOPLE(PERSON) VALUES('OSCAR')");
            pstmt.executeUpdate();
         } catch( Exception e ) { 
             throw new RuntimeException( e );
         }
         return "";
     }
%>
:)
<%
    getData();
%>

And execute your jsp again by going to localhost:8080/your/Hello.jsp

If you execute it twice the system will tell you the table already exists:

That's ok, we have created the table already.

Use a library to output JSON

Shudown tomcat, but pressing contrl-c

Download and copy to your WEB-INF/lib directory the json-simple jar. You can get it from here

Start tomcat again

Comment the creation code in the JSP and replace it for a SQL query like this:

<%@page import="java.sql.*, java.util.*, org.json.simple.JSONValue"%>

<%!
     public String getData() {
         List list = new ArrayList();
         Connection connection = null;
         try {
             Class.forName("org.apache.derby.jdbc.EmbeddedDriver");
              connection = DriverManager.getConnection("jdbc:derby:yourdb;create=true");
             // The first time:
             //PreparedStatement pstmt = connection.prepareStatement(
             //    "CREATE TABLE PEOPLE\n"+
             //    "(PERSON_ID INT NOT NULL GENERATED ALWAYS AS IDENTITY\n"+
             //    "    CONSTRAINT PEOPLE_PK PRIMARY KEY, PERSON VARCHAR(26))");
            //pstmt.executeUpdate();
            //pstmt = connection.prepareStatement("INSERT INTO PEOPLE(PERSON) VALUES('OSCAR')");
            //pstmt.executeUpdate();
            // execute select the second time
            PreparedStatement psmt = connection.prepareStatement("SELECT person FROM PEOPLE");
            ResultSet rs = psmt.executeQuery();
            while( rs.next() ){
                list.add( rs.getString("person"));
            }
         } catch( Exception e ) { 
             throw new RuntimeException( e );
         } finally {
             if( connection != null ) try {
                 connection.close();
             } catch( Exception e ){}
         }
         return JSONValue.toJSONString(list);
     }
%>
:)

Notice we are using a throw import, and at the end, we change the invocation of the method to put the result in a javascript variable list

When run, the JSP page would look like this ( you'll have to right click to see the HTML source code so see the