Java 杂记

追加数据到文件

try {
    File file = new File(getBasePath() + statistic + "ip.txt");
    // 如果文件不存在就会创建,然后追加数据
    FileWriter fw = new FileWriter(file, true);
    PrintWriter pw = new PrintWriter(fw);
    pw.println(ip);

    pw.flush();
    fw.flush();

    pw.close();
    fw.close();
} catch (IOException e) {
    e.printStackTrace();
}

重写equals的要点

1. 自反性 x.equals(x)为true
2. 对称性 x.equals(y)为true y.equals(x)也为true
3. 传递性 x.equals(y)为true y.equals(z)也为true 则 x.equals(z)为true
4. 一致性 当两个对象均未被修改时,反复调用x.equals(y)总会返回相同的值
5. 非空性 x.equals(null) 返回false

    private int equ;
    @Override
    public boolean equals(Object obj) {
        
        if(this == obj) return true;
        if(obj == null) return false;
        if(this.getClass() != obj.getClass()) return false;
        
        Equals that = (Equals) obj;
        if(this.equ != that.equ) return false;
        return true;
    }

BaseDao

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

//import javax.naming.Context;
//import javax.naming.InitialContext;
//import javax.sql.DataSource;
/**打开和关闭数据库连接的工具类，基础Dao*/
public class BaseDao {
    private static final String URL="jdbc:sqlserver://localhost:1433;DatabaseName=数据库名称";
    private static final String UNAME="sa";
    private static final String PWD="ok";
    static{//加载驱动，静态代码块，整个程序运行期间，仅会执行一次
        try {
            Class.forName("com.microsoft.sqlserver.jdbc.SQLServerDriver");
        } catch (ClassNotFoundException e) { e.printStackTrace(); }
    }
    protected Connection conn;
    protected PreparedStatement ps;
    protected ResultSet rs;
    public void open(){/**打开数据库连接*/
        try {
//       Context context = new InitialContext();
//       DataSource ds=(DataSource)context.lookup("java:comp/env/数据池名称");
//       conn = ds.getConnection();
            conn = DriverManager.getConnection(URL, UNAME, PWD);
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
    public void close(){
        try {
            if(rs!=null)   rs.close();
            if(ps!=null)   ps.close();
            if(conn!=null) conn.close();
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
    public int update(String sql, Object... params) {
        int count = 0 ;
        try {
            open();
            ps = conn.prepareStatement(sql);
            for (int i = 0; i < params.length; i++) {
                ps.setObject(i+1, params[i]);
            }
            count = ps.executeUpdate();
        } catch (SQLException e) {
            e.printStackTrace();
        }finally{
            close();
        }

        return count;
    }

    public void query(String sql, Object... params) {
        try {
            open();
            ps = conn.prepareStatement(sql);
            for (int i = 0; i < params.length; i++) {
                ps.setObject(i+1, params[i]);
            }
            rs = ps.executeQuery();
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }


}

MyBatisUtil

import java.io.IOException;
import java.io.Reader;

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;

public class MybatisUtil {

    private static final String FILENAME ="mybatis_config.xml";
    private static SqlSessionFactory ssfactory;
    static{// 只在加载时创建一次工厂
        try {
            Reader reader = Resources.getResourceAsReader(FILENAME);
            ssfactory = new SqlSessionFactoryBuilder().build(reader);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    // 线程变量， 在共有的资源中，为每一个线程分配一个独立的资源，防止本线程中的资源被另外一个资源使用
    private static ThreadLocal<SqlSession> threadLocal = new ThreadLocal<SqlSession>();
    /**
     * 打开SqlSession连接
     * @return
     */
    public static SqlSession getSqlSession() {
        SqlSession sqlSession = threadLocal.get();
        if (sqlSession == null) {
            threadLocal.set(ssfactory.openSession());
            sqlSession = threadLocal.get();
        }
        return sqlSession;
    }
    /**
     * 关闭SqlSession连接
     */
    public static void closeSqlsession() {
        SqlSession sqlSession = threadLocal.get();
        if (sqlSession != null) {
            sqlSession.close();
            threadLocal.set(null);
        }
    }
}

Page工具类

import java.util.List;

public class Paging<T> {

    //页面大小常量
    public static final int PAGESIZE_5 = 5;
    public static final int PAGESIZE_10 = 10;
    public static final int PAGESIZE_15 = 15;
    public static final int PAGESIZE_20 = 20;

    private int pageSize;//每页行数
    private int totalCount;//总行数
    private int totalPageCount;//总页数
    private int currPageNo;//当前页数
    private List<T> data;

    public List<T> getData() {
        return data;
    }
    public void setData(List<T> data) {
        this.data = data;
    }
    public int getPageSize() {
        return pageSize;
    }
    public void setPageSize(int pageSize) {
        this.pageSize = pageSize;
    }
    public int getTotalCount() {
        return totalCount;
    }
    public void setTotalCount(int totalCount) {
        this.totalCount = totalCount;
        totalPageCount = (totalCount%pageSize == 0)? (totalCount/pageSize) : (totalCount/pageSize)+1;
    }
    public int getTotalPageCount() {
        return totalPageCount;
    }
    public void setTotalPageCount(int totalPageCount) {
        this.totalPageCount = totalPageCount;
    }
    public int getCurrPageNo() {//----------------------------------
        // 因为totalCount可能因为查不到结果为0,所以totalPageCount计算出来为0 即使前面默认的currPageNo=1总是大于0
        // 所以currPageNo=totalPageCount=0 进入查询0-1=-1所以报错 加判断回避
        if(currPageNo < 1){
            currPageNo=1;
        }else if(currPageNo > totalPageCount && totalPageCount != 0 ){
            currPageNo=totalPageCount;
        }
        return currPageNo;
    }
    public void setCurrPageNo(int currPageNo) {
        this.currPageNo = currPageNo;
    }


}

转载于:https://www.jianshu.com/p/27a4765f935a