Java 常用代码汇总

谁借莪１个温暖的怀抱￠ 2022-09-16 00:20 213阅读 0赞

1. 字符串有整型的相互转换

String a = String.valueOf(2); //integer to numeric string
    int i = Integer.parseInt(a); //numeric string to an int

### **2. 向文件末尾添加内容** ###

BufferedWriter out = null;
    try {
      out = new BufferedWriter(new FileWriter(”filename”, true));
      out.write(”aString”);
    } catch (IOException e) {
      // error processing code
    } finally {
      if (out != null) {
        out.close();
      }
    }

### **3. 得到当前方法的名字** ###

String methodName = Thread.currentThread().getStackTrace()[1].getMethodName();

### **4. 转字符串到日期** ###

java.util.Date = java.text.DateFormat.getDateInstance().parse(date String);
    或者是：
    SimpleDateFormat format = new SimpleDateFormat( "yyyy-MM-dd" );
    Date date = format.parse( myString );

### **5. 使用JDBC链接Oracle** ###

public class OracleJdbcTest 
    {
      String driverClass = "oracle.jdbc.driver.OracleDriver";
      Connection con;
      public void init(FileInputStream fs) throws ClassNotFoundException, SQLException, FileNotFoundException, IOException
    {
        Properties props = new Properties();
        props.load(fs);
        String url = props.getProperty("db.url");
        String userName = props.getProperty("db.user");
        String password = props.getProperty("db.password");
        Class.forName(driverClass);
        con=DriverManager.getConnection(url, userName, password);
      }
      public void fetch() throws SQLException, IOException
    {
        PreparedStatement ps = con.prepareStatement("select SYSDATE from dual");
        ResultSet rs = ps.executeQuery();
        while (rs.next())
        {
          // do the thing you do
        }
        rs.close();
        ps.close();
      }
      public static void main(String[] args) 
    {
        OracleJdbcTest test = new OracleJdbcTest();
        test.init();
        test.fetch();
      }
    }

### **6.列出文件和目录** ###

File dir = new File("directoryName");
     String[] children = dir.list();
     if (children == null) {
       // Either dir does not exist or is not a directory
     } else {
       for (int i=0; i < children.length; i++) {
         // Get filename of file or directory
         String filename = children[i];
       }
     }
     // It is also possible to filter the list of returned files.
     // This example does not return any files that start with `.'.
     FilenameFilter filter = new FilenameFilter() {
       public boolean accept(File dir, String name) {
         return !name.startsWith(".");
       }
     };
     children = dir.list(filter);
     // The list of files can also be retrieved as File objects
     File[] files = dir.listFiles();
     // This filter only returns directories
     FileFilter fileFilter = new FileFilter() {
       public boolean accept(File file) {
         return file.isDirectory();
       }
     };
     files = dir.listFiles(fileFilter);

### **7.解析/读取XML 文件** ###

<?xml version="1.0"?>
    <students>
    <student>
    <name>John</name>
    <grade>B</grade>
    <age>12</age>
    </student>
    <student>
    <name>Mary</name>
    <grade>A</grade>
    <age>11</age>
    </student>
    <student>
    <name>Simon</name>
    <grade>A</grade>
    <age>18</age>
    </student>
    </students>

### **8. java分页代码实现** ###

1 public class PageBean {  
    2     private int curPage; //当前页 
    3     private int pageCount; //总页数 
    4     private int rowsCount; //总行数 
    5     private int pageSize=10; //每页多少行 
    6
    7
     8    
    9     public PageBean(int rows){ 
    10
    11         this.setRowsCount(rows); 
    12         if(this.rowsCount % this.pageSize == 0){ 
    13             this.pageCount=this.rowsCount / this.pageSize; 
    14         } 
    15         else if(rows<this.pageSize){ 
    16             this.pageCount=1; 
    17         } 
    18         else{ 
    19             this.pageCount=this.rowsCount / this.pageSize +1; 
    20         } 
    21     } 
    22
    23
    24     public int getCurPage() { 
    25         return curPage; 
    26     } 
    27     public void setCurPage(int curPage) { 
    28         this.curPage = curPage; 
    29     } 
    30     public int getPageCount() { 
    31         return pageCount; 
    32     } 
    33     public void setPageCount(int pageCount) { 
    34         this.pageCount = pageCount; 
    35     } 
    36     public int getPageSize() { 
    37         return pageSize; 
    38     } 
    39     public void setPageSize(int pageSize) { 
    40         this.pageSize = pageSize; 
    41     } 
    42     public int getRowsCount() { 
    43         return rowsCount; 
    44     } 
    45     public void setRowsCount(int rowsCount) { 
    46         this.rowsCount = rowsCount; 
    47     } 
    48 }

### **分页展示如下** ###

1 List clist=adminbiz.queryNotFullCourse();//将查询结果存放在List集合里 
     2 PageBean pagebean=new PageBean(clist.size());//初始化PageBean对象 
     3 //设置当前页 
     4 pagebean.setCurPage(page); //这里page是从页面上获取的一个参数，代表页数 
     5 //获得分页大小 
     6 int pagesize=pagebean.getPageSize(); 
     7 //获得分页数据在list集合中的索引 
     8 int firstIndex=(page-1)*pagesize; 
     9 int toIndex=page*pagesize; 
    10 if(toIndex>clist.size()){ 
    11     toIndex=clist.size(); 
    12 } 
    13 if(firstIndex>toIndex){ 
    14     firstIndex=0; 
    15     pagebean.setCurPage(1); 
    16 } 
    17 //截取数据集合，获得分页数据 
    18 List courseList=clist.subList(firstIndex, toIndex);