JAVA JDBC 连接Mysql 更新数据 双表查询更新

package com.test.json;package com.test.javahome;import java.sql.Connection;import java.sql.DriverManager;import java.sql.ResultSet;import java.sql.SQLException;import java.sql.Statement;import java.util.ArrayList;public class DataBaseTest {    private static final String TABLE_01 = "dizhi2";    private static final String TABLE_02 = "real_480";    public static Connection getConnection() throws SQLException, java.lang.ClassNotFoundException {        // 第一步：加载MySQL的JDBC的驱动        Class.forName("com.mysql.jdbc.Driver");        // 取得连接的url,能访问MySQL数据库的用户名,密码；studentinfo：数据库名        String url = "jdbc:mysql://localhost:3306/wumigen";        String username = "root";        String password = "qwert";        // 第二步：创建与MySQL数据库的连接类的实例        System.out.println("main ==============begin2");        Connection con = DriverManager.getConnection(url, username, password);        System.out.println("main ==============begin3");        return con;    }    public static void main(String args[]) {        try {            System.out.println("main ==============begin");            Connection con = getConnection();            System.out.println("main ==============begin4");            Statement sql_statement = con.createStatement();            String query1 = "select * from "+TABLE_01;            String query2 = "select * from "+TABLE_02;            System.out.println("query1 ==============begin");            ResultSet result = sql_statement.executeQuery(query1);            ArrayList<px> pxlist = new ArrayList<px>();            while (result.next()) {                PX p1 = new PX();                p1.type = result.getString(2);                p1.number = result.getString(3);                p1.img_320 = result.getString(4);                pxlist.add(p1);            }            System.out.println("query1 ==============end, size = " + pxlist.size());            System.out.println("query2 ==============begin");            ResultSet result2 = sql_statement.executeQuery(query2);            ArrayList<py> pylist = new ArrayList<py>();            while (result2.next()) {                PY p2 = new PY();                p2.number = result2.getString(2);                p2.img_480 = result2.getString(3);                pylist.add(p2);            }            for (int i = 0; i < pxlist.size(); i++) {                for (int j = 0; j < pylist.size(); j++) {                    if (pylist.get(j).number == pxlist.get(i).number) {                        pxlist.get(i).img_480 = pylist.get(j).img_480;                    }                }                if (pxlist.get(i).img_320.length() == 0) {                    System.out.println("=========null " + pxlist.get(i).number);                } else {                    String updateSql = "update "+TABLE_01+" set img_480='" + pxlist.get(i).img_480+                            "' where number='"+ pxlist.get(i).number + "'";                   System.out.println("begin to update ==> "+i);                    sql_statement.execute(updateSql);                }            }            System.out.println("query2 ==============end, size = " + pylist.size());            sql_statement.close();            con.close();            System.out.println("=========end ");        } catch (java.lang.ClassNotFoundException e) {            System.err.print("ClassNotFoundException");            System.err.println(e.getMessage());        } catch (SQLException ex) {            ex.printStackTrace();            System.err.println("SQLException: " + ex.getMessage());        }    }}class PX {    String type;    String number;    String img_320;    String img_480;}class PY {    String number;    String img_480;}</py></py></px></px>