PostgreSQL – JAVA 接口
PostgreSQL – JAVA 接口
安装
在我们开始在 Java 程序中使用 PostgreSQL 之前，我们需要确保我们在机器上设置了 PostgreSQL JDBC 和 Java。您可以查看 Java 教程以在您的机器上安装 Java。现在让我们检查如何设置 PostgreSQL JDBC 驱动程序。
-
从postgresql-jdbc存储库下载最新版本的postgresql-(VERSION).jdbc.jar。
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在您的类路径中添加下载的 jar 文件postgresql-(VERSION).jdbc.jar，或者您可以将它与 -classpath 选项一起使用，如下面的示例中所述。
以下部分假设您对 Java JDBC 概念知之甚少。如果您没有，那么建议您花半个小时学习JDBC 教程，以熟悉下面解释的概念。
连接到数据库
以下 Java 代码显示了如何连接到现有数据库。如果数据库不存在，则将创建它并最终返回一个数据库对象。
import java.sql.Connection;
import java.sql.DriverManager;
public class PostgreSQLJDBC {
public static void main(String args[]) {
Connection c = null;
try {
Class.forName("org.postgresql.Driver");
c = DriverManager
.getConnection("jdbc:postgresql://localhost:5432/testdb",
"postgres", "123");
} catch (Exception e) {
e.printStackTrace();
System.err.println(e.getClass().getName()+": "+e.getMessage());
System.exit(0);
}
System.out.println("Opened database successfully");
}
}
在编译和运行上面的程序之前，在 PostgreSQL 安装目录中找到pg_hba.conf文件并添加以下行 –
# IPv4 local connections: host all all 127.0.0.1/32 md5
您可以使用以下命令启动/重新启动 postgres 服务器，以防它没有运行 –
[root@host]# service postgresql restart Stopping postgresql service: [ OK ] Starting postgresql service: [ OK ]
现在，让我们编译并运行上面的程序来连接 testdb。在这里，我们使用postgres作为用户 ID 和123作为密码来访问数据库。您可以根据您的数据库配置和设置进行更改。我们还假设当前版本的 JDBC 驱动程序postgresql-9.2-1002.jdbc3.jar在当前路径中可用。
C:\JavaPostgresIntegration>javac PostgreSQLJDBC.java C:\JavaPostgresIntegration>java -cp c:\tools\postgresql-9.2-1002.jdbc3.jar;C:\JavaPostgresIntegration PostgreSQLJDBC Open database successfully
创建表
以下 Java 程序将用于在先前打开的数据库中创建表。确保您的目标数据库中没有此表。
import java.sql.*;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.Statement;
public class PostgreSQLJDBC {
public static void main( String args[] ) {
Connection c = null;
Statement stmt = null;
try {
Class.forName("org.postgresql.Driver");
c = DriverManager
.getConnection("jdbc:postgresql://localhost:5432/testdb",
"manisha", "123");
System.out.println("Opened database successfully");
stmt = c.createStatement();
String sql = "CREATE TABLE COMPANY " +
"(ID INT PRIMARY KEY NOT NULL," +
" NAME TEXT NOT NULL, " +
" AGE INT NOT NULL, " +
" ADDRESS CHAR(50), " +
" SALARY REAL)";
stmt.executeUpdate(sql);
stmt.close();
c.close();
} catch ( Exception e ) {
System.err.println( e.getClass().getName()+": "+ e.getMessage() );
System.exit(0);
}
System.out.println("Table created successfully");
}
}
当一个程序被编译和执行时，它将在testdb数据库中创建 COMPANY 表并显示以下两行 –
Opened database successfully Table created successfully
插入操作
以下 Java 程序显示了如何在上面示例中创建的 COMPANY 表中创建记录 –
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.Statement;
public class PostgreSQLJDBC {
public static void main(String args[]) {
Connection c = null;
Statement stmt = null;
try {
Class.forName("org.postgresql.Driver");
c = DriverManager
.getConnection("jdbc:postgresql://localhost:5432/testdb",
"manisha", "123");
c.setAutoCommit(false);
System.out.println("Opened database successfully");
stmt = c.createStatement();
String sql = "INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY) "
+ "VALUES (1, 'Paul', 32, 'California', 20000.00 );";
stmt.executeUpdate(sql);
sql = "INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY) "
+ "VALUES (2, 'Allen', 25, 'Texas', 15000.00 );";
stmt.executeUpdate(sql);
sql = "INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY) "
+ "VALUES (3, 'Teddy', 23, 'Norway', 20000.00 );";
stmt.executeUpdate(sql);
sql = "INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY) "
+ "VALUES (4, 'Mark', 25, 'Rich-Mond ', 65000.00 );";
stmt.executeUpdate(sql);
stmt.close();
c.commit();
c.close();
} catch (Exception e) {
System.err.println( e.getClass().getName()+": "+ e.getMessage() );
System.exit(0);
}
System.out.println("Records created successfully");
}
}
当上述程序被编译和执行时，它会在 COMPANY 表中创建给定的记录并显示以下两行 –
Opened database successfully Records created successfully
选择操作
以下 Java 程序显示了我们如何从上面示例中创建的 COMPANY 表中获取和显示记录 –
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;
public class PostgreSQLJDBC {
public static void main( String args[] ) {
Connection c = null;
Statement stmt = null;
try {
Class.forName("org.postgresql.Driver");
c = DriverManager
.getConnection("jdbc:postgresql://localhost:5432/testdb",
"manisha", "123");
c.setAutoCommit(false);
System.out.println("Opened database successfully");
stmt = c.createStatement();
ResultSet rs = stmt.executeQuery( "SELECT * FROM COMPANY;" );
while ( rs.next() ) {
int id = rs.getInt("id");
String name = rs.getString("name");
int age = rs.getInt("age");
String address = rs.getString("address");
float salary = rs.getFloat("salary");
System.out.println( "ID = " + id );
System.out.println( "NAME = " + name );
System.out.println( "AGE = " + age );
System.out.println( "ADDRESS = " + address );
System.out.println( "SALARY = " + salary );
System.out.println();
}
rs.close();
stmt.close();
c.close();
} catch ( Exception e ) {
System.err.println( e.getClass().getName()+": "+ e.getMessage() );
System.exit(0);
}
System.out.println("Operation done successfully");
}
}
当程序被编译和执行时，它会产生以下结果 –
Opened database successfully ID = 1 NAME = Paul AGE = 32 ADDRESS = California SALARY = 20000.0 ID = 2 NAME = Allen AGE = 25 ADDRESS = Texas SALARY = 15000.0 ID = 3 NAME = Teddy AGE = 23 ADDRESS = Norway SALARY = 20000.0 ID = 4 NAME = Mark AGE = 25 ADDRESS = Rich-Mond SALARY = 65000.0 Operation done successfully
更新操作
以下 Java 代码显示了我们如何使用 UPDATE 语句更新任何记录，然后从我们的 COMPANY 表中获取并显示更新的记录 –
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;
public class PostgreSQLJDBC {
public static void main( String args[] ) {
Connection c = null;
Statement stmt = null;
try {
Class.forName("org.postgresql.Driver");
c = DriverManager
.getConnection("jdbc:postgresql://localhost:5432/testdb",
"manisha", "123");
c.setAutoCommit(false);
System.out.println("Opened database successfully");
stmt = c.createStatement();
String sql = "UPDATE COMPANY set SALARY = 25000.00 where ID=1;";
stmt.executeUpdate(sql);
c.commit();
ResultSet rs = stmt.executeQuery( "SELECT * FROM COMPANY;" );
while ( rs.next() ) {
int id = rs.getInt("id");
String name = rs.getString("name");
int age = rs.getInt("age");
String address = rs.getString("address");
float salary = rs.getFloat("salary");
System.out.println( "ID = " + id );
System.out.println( "NAME = " + name );
System.out.println( "AGE = " + age );
System.out.println( "ADDRESS = " + address );
System.out.println( "SALARY = " + salary );
System.out.println();
}
rs.close();
stmt.close();
c.close();
} catch ( Exception e ) {
System.err.println( e.getClass().getName()+": "+ e.getMessage() );
System.exit(0);
}
System.out.println("Operation done successfully");
}
}
当程序被编译和执行时，它会产生以下结果 –
Opened database successfully ID = 2 NAME = Allen AGE = 25 ADDRESS = Texas SALARY = 15000.0 ID = 3 NAME = Teddy AGE = 23 ADDRESS = Norway SALARY = 20000.0 ID = 4 NAME = Mark AGE = 25 ADDRESS = Rich-Mond SALARY = 65000.0 ID = 1 NAME = Paul AGE = 32 ADDRESS = California SALARY = 25000.0 Operation done successfully
删除操作
以下 Java 代码显示了我们如何使用 DELETE 语句删除任何记录，然后从我们的 COMPANY 表中获取并显示剩余的记录 –
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;
public class PostgreSQLJDBC6 {
public static void main( String args[] ) {
Connection c = null;
Statement stmt = null;
try {
Class.forName("org.postgresql.Driver");
c = DriverManager
.getConnection("jdbc:postgresql://localhost:5432/testdb",
"manisha", "123");
c.setAutoCommit(false);
System.out.println("Opened database successfully");
stmt = c.createStatement();
String sql = "DELETE from COMPANY where ID = 2;";
stmt.executeUpdate(sql);
c.commit();
ResultSet rs = stmt.executeQuery( "SELECT * FROM COMPANY;" );
while ( rs.next() ) {
int id = rs.getInt("id");
String name = rs.getString("name");
int age = rs.getInt("age");
String address = rs.getString("address");
float salary = rs.getFloat("salary");
System.out.println( "ID = " + id );
System.out.println( "NAME = " + name );
System.out.println( "AGE = " + age );
System.out.println( "ADDRESS = " + address );
System.out.println( "SALARY = " + salary );
System.out.println();
}
rs.close();
stmt.close();
c.close();
} catch ( Exception e ) {
System.err.println( e.getClass().getName()+": "+ e.getMessage() );
System.exit(0);
}
System.out.println("Operation done successfully");
}
}
当程序被编译和执行时，它会产生以下结果 –
Opened database successfully ID = 3 NAME = Teddy AGE = 23 ADDRESS = Norway SALARY = 20000.0 ID = 4 NAME = Mark AGE = 25 ADDRESS = Rich-Mond SALARY = 65000.0 ID = 1 NAME = Paul AGE = 32 ADDRESS = California SALARY = 25000.0 Operation done successfully
