java操作

1.list转map(将某一列作为key)

final ImmutableMap<Long, Position> indexPosition = Maps.uniqueIndex(
            positionList, new Function<Position, Long>() {
                @Override
                public Long apply(Position input) {
                    return input.getId();
                }
            });

2.list.indexof()查找的是指针：

List<Pet> pets = new ArrayList<Pet>();
pets.add(new Cat());
Cat cat=new Cat();
System.out.println(pets.indexOf(cat));
//output:-1

3.判断列表为空

public static List<Integer> listEmpty(List<String> strs) {
    if (CollectionUtils.isEmpty(strs)){
        return Collections.emptyList();
    }

}

4.string赋值并且判断空

方法一：用guava，代码量反而大

String key = null;

String result = null;
try {
    result = Preconditions.checkNotNull(key, "-");
} catch (NullPointerException e) {
    result = e.getMessage();
}

方法二

String key = null;

String result = (key == null) ? "-" : key;

方法三:firstNonNull返回第一个非空对象，可以是自定义的类

String key = null;

String result = Objects.firstNonNull(key, "-");

5.带查找和排序的类设计

public class DemoVo {
    private Integer id;
    private String name;
    private Integer curPage;//当前页码
    private Integer pageSize;//分页大小
    private Integer offset;//数据偏移量
    private String sortby;//排序条件
    private String orderby;//排序方式

    //计算分页信息
    public Integer getOffset() {
        if (null == offset) {
            offset = (curPage - 1) * pageSize;
        }
        return offset;
    }

    //排序列取值范围
    public static final ImmutableMap<String, String> SORTBY_MAP = ImmutableMap.of("id", "id", "name", "name");

    public static final ImmutableSet<String> ORDERBY_SET = ImmutableSet.of("asc", "desc");

     默认分页大小
    public static final int DEFAULT_PAGESIZE = 30;
    /**
     * 默认当前页码
     */
    public static final int DEFAULT_CURPAGE = 1;
    /**
     * 默认排序
     */
    public static final String DEFAULT_SORTBY = "name";
    /**
     * 默认排序方式
     */
    public static final String DEFAULT_ORDERBY = "asc";
}

排序设置方法

DemoVo demoVo = new DemoVo();
if (!Strings.isNullOrEmpty(sortby) && demoVo.SORTBY_MAP.containsKey(sortby)) {
    demoVo.setSortby(sortby);
}
if (!Strings.isNullOrEmpty(orderby) && demoVo.ORDERBY_SET.contains(orderby)) {
    demoVo.setOrderby(orderby);
}

6.生成不可变map

(1)kay,value都是string

public static final ImmutableMap<String, String> RANDOMS_VALUE=new ImmutableMap.Builder<String, String>().put("String","'abc'").put("Long", "123456")
        .put("Integer", "123").put("Date", "20150401").put("Byte", "1").build();

(2)其他

public static final ImmutableMap<Integer, String> RANDOM=ImmutableMap.of(1, "a", 2, "b");

7.CharMatcher

判断是否包含某些字符

CharMatcher charMatcher=CharMatcher.anyOf("@*");
String key="asdf234@#$";

if (charMatcher.matchesAnyOf(key)){
    System.out.println("it contains");
}

去掉首尾空格

String value=" private integer value";
String newStr=CharMatcher.WHITESPACE.trimAndCollapseFrom(value, ' ');

去掉尾部；号

String one="ahaha;";
    CharMatcher charMatcher=CharMatcher.anyOf(";");
    String two=charMatcher.trimTrailingFrom(one);

8.取出List的某一列

public static void test1(){
    Person person1=new Person("a",18);
    Person person2=new Person("b", 2);

    List<Person> persons=Lists.newArrayList();
    persons.add(person1);
    persons.add(person2);

    List<String> names=Lists.transform(persons, new Function<Person, String>() {
        public String apply(Person arg0) {
            // TODO Auto-generated method stub
            return arg0.getName();
        }
    });

    System.out.println(Joiner.on(",").join(names));
}

9.httpclient post带参数

//url及参数
    String url = URL;
    String resource = RESOURCE;
    String param=PARAMS;

    HttpClient client = new HttpClient();
    client.setConnectionTimeout(30000);
    client.setTimeout(30000);

    PostMethod post = new PostMethod(url);

    NameValuePair[] params =
            { new NameValuePair("resource", resource),
                    new NameValuePair("params", param), };

    post.setRequestBody(params);

    try {
        Integer statusCode = client.executeMethod(post);
        return post.getResponseBodyAsString();
    } catch (Exception e) {
        // TODO: handle exception
        log.info("fengchao http error" + url, e);
    } finally {
        post.releaseConnection();
    }

10.数据库表结构相同的两个表，java端赋值实体：

App app=new App();
AppHis appHis=new AppHis();
BeanUtils.copyProperties(appHis, app);

11.CaseFormat做字符转换

> CaseFormat-->caseFormat

String head = "CaseFormat";
    String name = CaseFormat.UPPER_CAMEL.to(CaseFormat.LOWER_CAMEL, head);
    System.out.println(name);
    //caseFormat

格式，示例：

LOWER_CAMEL lowerCamel

LOWER_HYPHEN lower-hyphen

LOWER__UNDERSCORE lower_underscore

UPPER_CAMEL UpperCamel

UPPERUNDERSCORE UPPERUNDERSCORE

12.springmvc 传入实例的列表

@Data
public class Dormitory {

    private Long id;

    private List<Member> members;

    private String memberString;

    public List<Member> getMembers(){
        if (!members.isEmpty()){
            return members;
        }
        if (!Strings.isNullOrEmpty(memberString)){
            Gson gson=new Gson();
            members=gson.fromJson(memberString, new TypeToken<List<Member>>()){             
            }.getType());
        }
        return Collections.emptyList();                 
    }       
}

springmvc无法直接传入列表,将数据传给string，重写列表的get方法，用gson自己解

gson可以用来在json和对象间转换，json和泛型list转换：

Dormitory dormitory = new Dormitory();
dormitory.setId(1L);
dormitory.setName("haha");

// 类转json
Gson gson = new Gson();
String key = gson.toJson(dormitory);

System.out.println(key);

// json转类
Dormitory dorm = gson.fromJson(key, Dormitory.class);
System.out.println(dorm.getName());

13.map遍历：用entry

Map<Long, String> maps = Maps.newHashMap();
    maps.put(1L, "a");
    maps.put(2L, "b");

    for (Entry<Long, String> entry : maps.entrySet()) {
        Long key = entry.getKey();
        String value = entry.getValue();

        System.out.println(key + ":" + value);
    }

14.编码格式转换

unicode是一种编码规范，UTF-8属于规范的一种实现。

无论哪种格式，存储和传递的都是unicode编码数据

String key = "你好恩";
String key1 = new String(key.getBytes("UTF-8"), "gbk");

System.out.println(key1);

String key2 = new String(key1.getBytes("gbk"), "UTF-8");

System.out.println(key2);

15.按行读文件&string多个空格切分

File file = new File("d:\\date\\school_beijing.txt");

        List<String> lines = null;
        try {
            lines = Files.readLines(file, Charsets.UTF_8);
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

        for (String line : lines) {
            String name = line.split("\\s+")[1];
            System.out.print("('" + name + "',1),");
        }

16.取[min,max]范围的随机数

int s = random.nextInt(max)%(max-min+1) + min;

其中，random.nextInt(max)表示生成[0,max]之间的随机数

17.guava joiner：给字符串每一个中间插入'%'

String result = Joiner.on("%").join(Chars.asList(name.toCharArray()));

18.把对象和map互相转化

BeanUtils.describe:会把对象中的变量都转化成string

User user = …;
Map userMap = BeanUtils.describe(user);
//////////////
Map userMap = …;
User user = …;
BeanUtils.populate(user,userMap);

PropertyUtils.describe:变量是啥就是啥，因此转化成mybatis的参数时用这个

19.powermock静态方法 testng

1.静态方法，假设是个工具类：

public class Util {

    public static int getInt() {
        return 1;
    }   
}

2.被测试类Target

public class Target {
    public int findInt() {
        int key = Util.getInt();
        return key;
    }
}

3.测试类

import org.mockito.InjectMocks;
    import org.mockito.MockitoAnnotations;
    import org.powermock.api.mockito.PowerMockito;
    import org.powermock.core.classloader.annotations.PrepareForTest;
    import org.testng.Assert;
    import org.testng.annotations.BeforeClass;
    import org.testng.annotations.Test;

    @PrepareForTest({ Util.class })
    public class TargetTest {

        @InjectMocks
        private Target target;

        @BeforeClass
        public void setUp() {
            this.target = new Target();
            MockitoAnnotations.initMocks(this);
        }

        @Test
        public void targetTest() throws Exception {
            PowerMockito.mockStatic(Util.class);
            PowerMockito.doReturn(1).when(Util.class, "getInt");
            //如果有参数加到when()后面
            int key = target.findInt();
            Assert.assertEquals(1, key);
        }
    }

20.数组初始化与打印

int[] keys = { 1, 2, 3, 4, 5 };

    int[] ones = new int[10];

    int[] two = new int[] { 1, 2, 3, 4 };

    System.out.println(Arrays.toString(keys));

21.list移除元素：

使用iterator，因为list.remove()会改变size

public <T> void removeElement(List<T> list,T element){
    Iterator<T> iterator=list.iterator();
    while (iterator.hasNext()) {
        T t = (T) iterator.next();
        if (t.equals(element)){
            iterator.remove();
        }
    }
}

22.判断字符串字符集：

没有方法可以直接判断出来，只能看它是否是某个字符集：

if(key.equals(new String(key.getBytes("utf-8"), "utf-8"))){

　　 System.out.println("it is utf-8");
}

23.string转list<Long>("123,456,124")

List<Long> longs =   Lists.newArrayList(Iterables.transform(Splitter.on(',').split("1,2,3"), new Function<String, Long>() {
public Long apply(final String in) {
    return in == null ? null : Longs.tryParse(in);
}
}));

24.bigdecimal避免输出科学计数法：

return a.toPlainString()