您正在使用JDBC 3驱动程序。 JDBC 4驱动程序由 DriverManager 自动加载，而JDBC 3驱动程序则不加载。因此，您需要调用

  Class.forName（org.postgresql.Driver）; 
 

一次在您的应用程序中，（在调用 DriverManager＃getConnection $之前C $ C>）。

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或者，您可以使用这里不需要上述方法调用。

I wrote following the java program

import java.io.*;
import java.util.*;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.logging.Level;
import java.util.*;

public class Sample {
    public static void main (String[] args) throws IOException  {
                    int CountComputers;
            FileInputStream fstream = new FileInputStream(
                    "/export/hadoop-1.0.1/bin/countcomputers.txt");
            BufferedReader br = new BufferedReader(new InputStreamReader(fstream));
            String result=br.readLine();
            CountComputers=Integer.parseInt(result);
            input.close();
            fstream.close();
            Connection con = null;
            Statement st = null;
                ResultSet rs = null;    
               String url = "jdbc:postgresql://192.168.1.8:5432/NexentaSearch";
                String user = "postgres";
                String password = "valter89";
            ArrayList<String> paths = new ArrayList<String>();
            try
            {
                con = DriverManager.getConnection(url, user, password);
                        st = con.createStatement();
                        rs = st.executeQuery("select path from tasks order by id");
                while (rs.next()) { paths.add(rs.getString(1)); };
                PrintWriter zzz = null;
                    try
                    {
                            zzz = new PrintWriter(new FileOutputStream("/export/hadoop-1.0.1/bin/readwaysfromdatabase.txt"));
                    }
                    catch(FileNotFoundException e)
                    {
                            System.out.println("Error");
                            System.exit(0);
                    }
                    for (int i=0; i<paths.size(); i++)
                {
                    zzz.println("paths[i]=" + paths.get(i) + "\n");
                    }
                    zzz.close();

            }
            catch (SQLException e) 
            {
                System.out.println("Connection Failed! Check output console");
                e.printStackTrace();
            }
        }
}

I compiled this program and created the jar file

./javac -classpath /folder/postgresql-8.4-703.jdbc3.jar -d /Samplejavaprogram/classes /Samplejavaprogram/src/Sample.java
./jar -cvf /Samplejavaprogram/Sample.jar -C /Samplejavaprogram/classes/ .

Jar has the following manifest file

Manifest-Version: 1.0
Created-By: 1.7.0_06 (Oracle Corporation)
Main-Class: Sample
Class-Path: /folder/postgresql-8.4-703.jdbc3.jar

also contains file /folder/postgresql-8.4-703.jdbc3.jar. I launched Sample.jar by means of a command

./java -jar -Djava.library.path=/opt/jdk1.7.0_06/lib /Samplejavaprogram/Sample.jar

and as a result I received the following messages

Connection Failed! Check output console
java.sql.SQLException: No suitable driver found for jdbc:postgresql://192.168.1.8:5432/NexentaSearch
    at java.sql.DriverManager.getConnection(DriverManager.java:604)
    at java.sql.DriverManager.getConnection(DriverManager.java:221)
    at org.myorg.Sample.main(Sample.java:33)

I launched the file from a host with the address 192.168.1.10, and on a host 192.168.1.8 it fulfilled normally. Help to eliminate an error.

You are using a JDBC 3 driver. JDBC 4 drivers are loaded automatically loaded by the DriverManager whereas JDBC 3 drivers are not. Therefore you need to invoke

Class.forName("org.postgresql.Driver");

once in your application, (prior to invoking DriverManager#getConnection).

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Alternatively, you can use the JDBC 4 PostgreSQL driver from here which will not require the above method call.