List

根据某字段进行排序

Collections.sort()

//升序排列
Collections.sort(list, new Comparator<Student>() {
    public int compare(Student s1, Student s2) {
        return s1.getAge().compareTo(s2.getAge());
    }
});

//降序排列
Collections.sort(list, new Comparator<Student>() {
    public int compare(Student s1, Student s2) {
        return s2.getAge().compareTo(s1.getAge());
    }
});

//多条件-先年龄升序、后分数升序
Collections.sort(list, new Comparator<Student>() {
    public int compare(Student s1, Student s2) {
        int i = s1.getAge().compareTo(s2.getAge());
        if(i == 0) {
            i = s1.getScore().compareTo(s2.getScore());
        }
        return i;
    }
});

//如日期集合List<Date> list = new ArrayList<>();
Collections.sort(list, new Comparator<Date>() {
    public int compare(Date s1, Date s2) {
        return s1.compareTo(s2);
    }
});

list.sort()

//升序排列
list.sort((x,y)->Integer.compare(x.getAge(), y.getAge()));
//降序排列
list.sort((x,y)->Integer.compare(y.getAge(), x.getAge()));
//如日期集合List<Date> list = new ArrayList<>();
list.sort((x,y)->x.compareTo(y));

list.stream()

//升序排列
list = list.stream().sorted(Comparator.comparing(Student::getAge)).collect(Collectors.toList());
list = list.stream().sorted(Comparator.comparingInt(Student::getAge)).collect(Collectors.toList());
//使用lambda表达式
list = list.stream().sorted(Comparator.comparing(e -> e.getAge())).collect(Collectors.toList());
//降序排列
list = list.stream().sorted(Comparator.comparing(Student::getAge).reversed()).collect(Collectors.toList());
//多条件-先年龄升序、后分数升序
list = list.stream().sorted(Comparator.comparing(Student::getAge).thenComparing(Comparator.comparing(Student::getScore))).collect(Collectors.toList());

List转String去掉中括号和空格

   public static void main(String[] args) {
        List<String> list = new ArrayList();
        list.add("123");
        list.add("456");
        System.out.println("这时候的list转String" + list.toString());
        String str = list.toString().replaceAll("(?:\\[|null|\\]| +)", "");
        System.out.println("去掉括号和,之后的空格之后的" + str);
    }

ResultSet

ResultSet转List

public static List convertResultSetToList(ResultSet rs){
    List list = new ArrayList();
    try {
	ResultSetMetaData md = rs.getMetaData();//获取键名
	int columnCount = md.getColumnCount();//获取行的数量
	while (rs.next()) {
	    Map rowData = new HashMap();//声明Map
	    for (int i = 1; i <= columnCount; i++) {
	        rowData.put(md.getColumnName(i), rs.getObject(i));//获取键名及值
	    }
	    list.add(rowData);
	}
    } catch (Exception e) {
	// TODO Auto-generated catch block
	e.printStackTrace();
    }
    return list;
}

ResultSet转HashMapList

    public static ArrayList<HashMap<String, Object>> ResultToHashMapList(ResultSet rs) throws SQLException {
        ArrayList<HashMap<String, Object>> list = new ArrayList<>();
        ResultSetMetaData md = rs.getMetaData();//获取键名
        int columnCount = md.getColumnCount();//获取列的数量
        while (rs.next()) {
            HashMap<String, Object> rowData = new HashMap<>();
            for (int i = 1; i <= columnCount; i++) {
                rowData.put(md.getColumnName(i), rs.getObject(i));//获取键名及值
            }
            list.add(rowData);
        }
        return list;
    }