java学习总结

1 获得项目绝对路径

String path = request.getContextPath();
String basePath = request.getScheme() + "://" + request.getServerName() + ":" + request.getServerPort()
            + path + "/";

2 Java中List的排序

第一种方法，就是list中对象实现Comparable接口，代码如下：

public class Person implements Comparable<Person> {
    private String name;
    private Integer order;

    /**
     * @return the name
     */
    public String getName() {
        return name;
    }

    /**
     * @param name
     *            the name to set
     */
    public void setName(String name) {
        this.name = name;
    }

    /**
     * @return the order
     */
    public Integer getOrder() {
        return order;
    }

    /**
     * @param order
     *            the order to set
     */
    public void setOrder(Integer order) {
        this.order = order;
    }

    @Override
    public int compareTo(Person arg0) {
        return this.getOrder().compareTo(arg0.getOrder());
    }

}

测试例子

public static void main(String[] args) {
    List<Person> listA = new ArrayList<Person>();
    Person p1 = new Person();
    Person p2 = new Person();
    Person p3 = new Person();

    p1.setName("name1");
    p1.setOrder(1);
    p2.setName("name2");
    p2.setOrder(2);
    p3.setName("name3");
    p3.setOrder(3);

    listA.add(p2);
    listA.add(p1);
    listA.add(p3);
    Collections.sort(listA);
    for (Person p : listA) {
        System.out.println(p.getName());
    }
}

第二种方法，就是在重载Collections.sort方法，代码如下：

public class Person {
    private String name;
    private Integer order;

    /**
     * @return the name
     */
    public String getName() {
        return name;
    }

    /**
     * @param name
     *            the name to set
     */
    public void setName(String name) {
        this.name = name;
    }

    /**
     * @return the order
     */
    public Integer getOrder() {
        return order;
    }

    /**
     * @param order
     *            the order to set
     */
    public void setOrder(Integer order) {
        this.order = order;
    }

}

public static void main(String[] args) {
        List<Person> listA = new ArrayList<Person>();
        Person p1 = new Person();
        Person p2 = new Person();
        Person p3 = new Person();

        p1.setName("name1");
        p1.setOrder(1);
        p2.setName("name2");
        p2.setOrder(2);
        p3.setName("name3");
        p3.setOrder(3);

        listA.add(p2);
        listA.add(p1);
        listA.add(p3);

        Collections.sort(listA, new Comparator<Person>() {
            public int compare(Person arg0, Person arg1) {
                return arg0.getOrder().compareTo(arg1.getOrder());
            }
        });

        for (Person p : listA) {
            System.out.println(p.getName());
        }
    }

两次的执行结果，都是按照person对象的order进行升序排序。

两次执行的结果都是：

name1

name2

name3