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Yash edited this page Sep 30, 2019 · 1 revision

package com.github.jdbc

Standalone

public class DBConnection {
    public static void main(String[] args) throws SQLException {
        Connection conn = null;
        try {
            conn = DBConnection.getConnection("DEV");
        } finally {
            conn.close();
        }
    }
    
    static Map<String, String> connectionUrls = new HashMap<String, String>();
    static {
        // validationQuery="select 1 from dual", Host, Port, Sid (default=xe), userName, Password
        
        connectionUrls.put("DEV", "HostDEV~1521~xeDEV~xeDEV1~xeDEV777");
        connectionUrls.put("UAT", "HostUAT~1522~xeUAT~xeUAT1~xeUAT777");
    }
    public static Connection getConnection(String envKey) throws SQLException {
        Connection connection = null;
        OracleDriver driverClassName = new oracle.jdbc.driver.OracleDriver();
        try {
            java.sql.DriverManager.registerDriver(driverClassName);
            
            if (connectionUrls.containsKey(envKey)) {
                String uralParams = connectionUrls.get(envKey);
                String[] split = uralParams.split("~");
                
                StringBuffer buffer = new StringBuffer();
                buffer.append("jdbc:oracle:thin:@(DESCRIPTION=(ENABLE=BROKEN)(ADDRESS=(PROTOCOL=tcp)(PORT="+split[1]);
                buffer.append(")(HOST="+split[0]);
                buffer.append("))(CONNECT_DATA=(SID="+split[2]+")))");
                
                String usernName = split[3], password = split[4];
                
                // jdbc:oracle:driver_type:[username/password]@[//]host_name[:port][:ORCL]
                String connectionUrl = buffer.toString();
                System.out.println("DB URL: "+connectionUrl);
                // connection = DriverManager.getConnection("jdbc:default:connection:");
                //connection = DriverManager.getConnection(connectionUrl, usernName, password);
                
                // https://docs.oracle.com/javase/tutorial/jdbc/basics/connecting.html
                Properties connectionProps = new Properties();
                connectionProps.put("charset", "UTF8");
                connectionProps.put("lc_ctype", "en_US.UTF-8");
                connectionProps.put("user", usernName);
                connectionProps.put("password", password);
                
                connection = DriverManager.getConnection(connectionUrl, connectionProps);
                System.out.println("Connection : "+ connection);
            }
            return connection;
        } finally {
            DriverManager.deregisterDriver(driverClassName);
        }
    }
}

Server Context.xml

<?xml version="1.0" encoding="UTF-8"?>
<Context>
    <Environment name="contexEnvironmentDataSource" value="jdbc/yashoracle"
        type="java.lang.String" override="false" />
    <Environment name="contexEnvironmentDataSource2" value="jdbc/yashoracle2"
        type="java.lang.String" override="false" />

    <Resource name="jdbc/yashoracle" type="javax.sql.DataSource"
        username="yash" password="yashDB"
url="jdbc:oracle:thin:@(DESCRIPTION=(ENABLE=BROKEN)(ADDRESS=(PROTOCOL=tcp)(PORT=1521)(HOST=localhost))(CONNECT_DATA=(SID=xe)))"
        driverClassName="oracle.jdbc.driver.OracleDriver" maxTotal="20"
        maxIdle="10" maxWaitMillis="5000" minEvictableIdleTimeMillis="300000"
        timeBetweenEvictionRunsMillis="600000" validationInterval="600000"
        validationQuery="select 1 from dual" testOnBorrow="true" auth="Container"
        /> <!-- accessToUnderlyingConnectionAllowed="true" -->
</Context>
private static final String JNDI_SUBCONTEXT = "java:comp/env/";
public Connection getDataSourceConnection() {
    Connection connection = null;
    try {
        InitialContext initialContext = new InitialContext();
        String datasourceName = (String) initialContext.lookup(JNDI_SUBCONTEXT + "/contexEnvironmentDataSource");
        javax.sql.DataSource dataSource = (DataSource) initialContext.lookup(JNDI_SUBCONTEXT + "/" + datasourceName);
        connection = dataSource.getConnection();
    } catch (Exception e) {
        e.printStackTrace();
    }
    return connection;
}

In a class-based object-oriented language, in general, state is carried by instances, methods are carried by classes, and inheritance is only of structure and behavior.

Method signature: It consists of method name and parameter list (number/type/order of the parameters). methodName(parametersList y). An instance method in a subclass with the same signature and return type as an instance method in the super-class overrides the super-class's method.

Java OOP concepts
Class  - Collection of a common features of a group of object [static/instance Fields, blocks and Methods]
Object - Instance of a class (instance fields)
Abstraction - Process of hiding complex info and providing required info like API, Marker Interfaces ...
Encapsulation(Security) - Class Binding up with data members(fields) and member functions.
Inheritance  (Reusability by placing common code in single class)
 1. Multilevel - {A -> B -> C} 2. Multiple - Diamond problem {A <- (B) -> C} [Java not supports] 3. Cyclic {A <-> B} [Java not supports]
 * Is-A   Relation - Class A extends B
 * Hash-A Relation - Class A { B obj = new B(); } - (Composition/Aggregation)
Polymorphism (Flexibility) 1. Compile-Time Overloading    2. Runtime Overriding  [Greek - "many forms"]


int[] arr = {1,2,3}; int arrLength = arr.length;   // Fixed length of sequential blocks to hold same data type
String str = "Yash"; int strLength = str.length(); // Immutable Object value can't be changed.

List<?> collections = new ArrayList<String>(); int collectionGroupSize = collections.size();
Map<?, ?> mapEntry = new HashMap<String, String>();
Set<?> keySet = mapEntry.keySet(); // Set of Key's
Set<?> entrySet = mapEntry.entrySet(); // Set of Entries [Key, Value]

// Immutable Objects once created they can't be modified. final class Integer/String/Employee
Integer val = Integer.valueOf("100"); String str2 = String.valueOf(100); // Immutable classes
final class Employee { // All Wrapper classes, java.util.UUID, java.io.File ...
    private final String empName; // Field as Final(values can be assigned only once) Only getter functions.
    public Employee(String name) { this.empName = name; }
}

Native Java Code for Hashtable.h, Hashtable.cpp SQL API.

You can check your current JDK and JRE versions on your command prompt respectively,

  • JDK javac -version [C:\Program Files\Java\jdk1.8.0_121\bin] o/p: javac 1.8.0_121
  • JRE java -version [C:\Program Files\Java\jdk1.8.0_121\bin] o/P: java version "1.8.0_102"

JAVA_HOME - Must be set to JDK otherwise maven projects leads to compilation error. [ERROR] No compiler is provided in this environment. Perhaps you are running on a JRE rather than a JDK? C:\Softwares\OpenJDK\, 7-zip

Fatal error compiling: invalid target release: JRE and JDK must be of same version 1.8.0.XXX

Disable TLS 1.0 and 1.1security-libs/javax.net.ssl: TLS 1.0 and 1.1 are versions of the TLS protocol that are no longer considered secure and have been superseded by more secure and modern versions (TLS 1.2 and 1.3).

Core Java

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