JDBC MySQL执行SQL失败

Question

This is my code. I have a DB in MySQL which I use for processing. I referred to all the questions related to this exception. But none of them worked out for me. The problem is with the query I have used. When I make the query as

SELECT * FROM customers;

Then it works fine. But when I update it to following, exception will be thrown.

SELECT * FROM customer WHERE customer_id LIKE " + "'%" + consumerId + "%'

This is the exception I get.

com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure

The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server.
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:57)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:526)
    at com.mysql.jdbc.Util.handleNewInstance(Util.java:377)
    at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:1036)
    at com.mysql.jdbc.MysqlIO.readPacket(MysqlIO.java:627)
    at com.mysql.jdbc.MysqlIO.doHandshake(MysqlIO.java:1013)
    at com.mysql.jdbc.ConnectionImpl.coreConnect(ConnectionImpl.java:2234)
    at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2265)
    at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2064)
    at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:790)
    at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:44)
    at sun.reflect.GeneratedConstructorAccessor4.newInstance(Unknown Source)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:526)
    at com.mysql.jdbc.Util.handleNewInstance(Util.java:377)
    at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:395)
    at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:325)
    at java.sql.DriverManager.getConnection(DriverManager.java:571)
    at java.sql.DriverManager.getConnection(DriverManager.java:215)
    at com.smart.data.customer.CustomerInfoProvider.findDetails(CustomerInfoProvider.java:81)
    at com.smart.data.customer.CustomerInfoProvider.provideRequiredCustomerDetails(CustomerInfoProvider.java:28)
    at com.smart.data.manipulator.Starter.main(Starter.java:36)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:606)
    at com.intellij.rt.execution.application.AppMain.main(AppMain.java:120)
Caused by: java.io.EOFException: Can not read response from server. Expected to read 4 bytes, read 0 bytes before connection was unexpectedly lost.
    at com.mysql.jdbc.MysqlIO.readFully(MysqlIO.java:2914)
    at com.mysql.jdbc.MysqlIO.readPacket(MysqlIO.java:559)
    ... 22 more
Exception in thread "main" java.lang.NullPointerException
    at com.smart.data.customer.CustomerInfoProvider.provideRequiredCustomerDetails(CustomerInfoProvider.java:30)
    at com.smart.data.manipulator.Starter.main(Starter.java:36)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:606)
    at com.intellij.rt.execution.application.AppMain.main(AppMain.java:120)

package com.smart.data.customer;

import org.apache.log4j.Logger;

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.sql.*;
import java.util.ArrayList;
import java.util.Properties;

/**
 * Created with IntelliJ IDEA.
 * User: dulithdecozta
 * Date: 2/5/15
 * Time: 7:20 PM
 * To change this template use File | Settings | File Templates.
 */
public class CustomerInfoProvider {
    static Logger log = Logger.getLogger(CustomerInfoProvider.class.getName());
    ResultSet customerResultSet = null;
    Connection conn = null;

    public void provideRequiredCustomerDetails(ArrayList customerIdArraylist) {
        for (int i = 0; i < customerIdArraylist.size(); i++) {
            try {
                customerResultSet = findDetails(customerIdArraylist.get(i).toString());
                try {
                    while (customerResultSet.next()) {
                        try {
                            System.out.println("Fullname : " + customerResultSet.getString("fullname"));
                            System.out.println("Consumer ID : " + customerResultSet.getString("customer_id"));
                            System.out.println("City : " + customerResultSet.getString("city"));
                            System.out.println("gender : " + customerResultSet.getString("gender"));
                            System.out.println("Occupation : " + customerResultSet.getString("occupation"));
                            System.out.println(i);
                            System.out.println("*-*-*-*-*-*-*-*-*--*-*-*-*-*-*-*-*");
                        } catch (SQLException e) {
                            e.printStackTrace();
                        }
                    }
                } catch (SQLException e) {
                    e.printStackTrace();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        try {
            conn.close();
        } catch (SQLException e) {
            e.printStackTrace();  //To change body of catch statement use File | Settings | File Templates.
        }
    }

    public ResultSet findDetails(String consumerId) throws IOException {
        // Load property file
        Properties properties = new Properties();
        // Define an input stream
        InputStream inputStream = null;
        ResultSet rs = null;
        try {
            inputStream = new FileInputStream("/home/abc/Desktop/Jigi/database.properties"); // Path to the property file
        } catch (FileNotFoundException e) {
            log.debug("Exception encountered : File Not Found : ");
            e.printStackTrace();
        }
        try {
            // load a properties file
            properties.load(inputStream);
        } catch (IOException e) {
            log.debug("Exception encountered : A problem with the Input Stream : ");
            e.printStackTrace();
        }
        conn = null;
        Statement stmt = null;
        try {
            Class.forName(properties.getProperty("JDBC_DRIVER"));
            // log.debug("Connecting to database...!!");
            conn = DriverManager.getConnection(properties.getProperty("DB_URL"), properties.getProperty("USER"), properties.getProperty("PASS"));
            //    log.debug("Creating statement...!");
            stmt = conn.createStatement();
            rs = stmt.executeQuery("SELECT * FROM customer WHERE customer_id LIKE " + "'%" + consumerId + "%'");
        } catch (Exception ex) {
            ex.printStackTrace();
        }

        return rs;
    }
}

Answer 1

If my theory that your query takes too long is true, then you need to make the query take less time somehow.

You could try

 SELECT col1, col2, col3 
   FROM customer 
  WHERE customer_id LIKE '" +  consumerId + "%'"
  LIMIT 10

When you omit the leading % in the LIKE clause, you allow MySQL to use an index to find the right rows.

When you enumerate the columns you need from your query, you reduce the network traffic and allow MySQL to use some efficiencies in constructing the answer to your query.

When you say LIMIT 10 , you avoid the possibility that MySQL will try to return the whole table if your user makes a mistake and requests an empty string.

You should also use a bind parameter for your customerId value. You can look up how to do this with JDBC.

Answer 2

You could save those data into an array list and call that list when you need it. That would help you to prevent this exception. This is due to low response time of the query.

Answer 3

Changing the Query returned the results without giving the exception.

package com.smart.data.customer;

import org.apache.log4j.Logger;

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.sql.*;
import java.util.ArrayList;
import java.util.Properties;

/**
 * Created with IntelliJ IDEA.
 * User: dulithdecozta
 * Date: 2/5/15
 * Time: 7:20 PM
 * To change this template use File | Settings | File Templates.
 */
public class CustomerInfoProvider {
    static Logger log = Logger.getLogger(CustomerInfoProvider.class.getName());
    ResultSet customerResultSet = null;
    Connection conn = null;

    public void provideRequiredCustomerDetails(ArrayList customerIdArraylist) {
        for (int i = 0; i < customerIdArraylist.size(); i++) {
            try {
                customerResultSet = findDetails(customerIdArraylist.get(i).toString());
                try {
                    while (customerResultSet.next()) {
                        try {
                            System.out.println("Fullname : " + customerResultSet.getString("fullname"));
                            System.out.println("Consumer ID : " + customerResultSet.getString("customer_id"));
                            System.out.println("City : " + customerResultSet.getString("city"));
                            System.out.println("gender : " + customerResultSet.getString("gender"));
                            System.out.println("Occupation : " + customerResultSet.getString("occupation"));
                            System.out.println(i);
                            System.out.println("*-*-*-*-*-*-*-*-*--*-*-*-*-*-*-*-*");
                        } catch (SQLException e) {
                            e.printStackTrace();
                        }
                    }
                } catch (SQLException e) {
                    e.printStackTrace();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        try {
            conn.close();
        } catch (SQLException e) {
            e.printStackTrace();  //To change body of catch statement use File | Settings | File Templates.
        }
    }

    public ResultSet findDetails(String consumerId) throws IOException {
        // Load property file
        Properties properties = new Properties();
        // Define an input stream
        InputStream inputStream = null;
        ResultSet rs = null;
        try {
            inputStream = new FileInputStream("/home/abc/Desktop/Jigi/database.properties"); // Path to the property file
        } catch (FileNotFoundException e) {
            log.debug("Exception encountered : File Not Found : ");
            e.printStackTrace();
        }
        try {
            // load a properties file
            properties.load(inputStream);
        } catch (IOException e) {
            log.debug("Exception encountered : A problem with the Input Stream : ");
            e.printStackTrace();
        }
        conn = null;
        Statement stmt = null;
        try {
            Class.forName(properties.getProperty("JDBC_DRIVER"));
            // log.debug("Connecting to database...!!");
            conn = DriverManager.getConnection(properties.getProperty("DB_URL"), properties.getProperty("USER"), properties.getProperty("PASS"));
            //    log.debug("Creating statement...!");
            stmt = conn.createStatement();
            rs = stmt.executeQuery("SELECT * FROM customer WHERE customer_id=" +consumerId);
        } catch (Exception ex) {
            ex.printStackTrace();
        }

        return rs;
    }
}