Typecho guava是google开发的一个基础java类库，包括主要的模块为utilities/Functional/Collections/concurrency/cache/eventbus/work files，guava提供了很多好用的api，使用guava编程可以有效提高开发效率和代码质量。
Joiner(list/map转化为string)
private static final String COMMA = ",";
private static final String EMPTY = "";
private static final String EQUALS = "=";
public static String oldJoiner(List<String> dataList) {
// 老的方法实现
if (dataList == null) {
return null;
}
StringBuilder accum = new StringBuilder();
for (String item : dataList) {
accum.append(item == null ? EMPTY : item).append(COMMA);
}
String joinResult = accum.toString();
return joinResult.substring(0, joinResult.length() - 1);
}
public static String oldJoiner(Map<String,String> dataMap){
if (dataMap == null){
return null;
}
// 老的方式，转换代码和判断比较多
StringBuilder accum = new StringBuilder();
for (Map.Entry<String,String> item : dataMap.entrySet()) {
accum.append(item.getKey() == null ? EMPTY : item.getKey()).append(EQUALS).append(item.getValue()).append(COMMA);
}
String joinResult = accum.toString();
return joinResult.substring(0, joinResult.length() - 1);
}
public static String joiner(List<String> dataList) {
if (dataList == null) {
return null;
}
// guava的实现，该方法使用类似于python中的",".join(list)
return Joiner.on(COMMA).useForNull(EMPTY).join(dataList);
}
public static String appendTo(List<String> dataList){
return Joiner.on(COMMA).useForNull(EMPTY).appendTo(new StringBuilder(), dataList).toString();
}
public static String joiner(Map<String,String> dataMap){
if (dataMap == null){
return null;
}
// guava joiner将map值转化为string
return Joiner.on(COMMA).useForNull(EMPTY).withKeyValueSeparator(EQUALS).join(dataMap);
}
public static void main(String[] args) {
// 要求:将list转化为使用逗号分隔的字符串
List<String> dataList = Arrays.asList("1", "2", "3", null);
System.out.println(appendTo(dataList));
// 测试代码
TestUtil.assertIsTrue(TestUtil.equals(joiner(dataList), oldJoiner(dataList)), "值不等");
dataList = null;
TestUtil.assertIsTrue(TestUtil.equals(joiner(dataList), oldJoiner(dataList)), "值不等");
Map<String,String> dataMap = new HashMap<>(5);
dataMap.put("a","1");
dataMap.put("b","2");
dataMap.put("c","3");
dataMap.put(null,"4");
dataMap.put("e","5");
TestUtil.assertIsTrue(TestUtil.equals(joiner(dataMap), oldJoiner(dataMap)), "值不等");
dataMap = null;
TestUtil.assertIsTrue(TestUtil.equals(joiner(dataMap), oldJoiner(dataMap)), "值不等");
}Splitter(string转化为list/map)
private static final String COMMA = ",";
private static final String EMPTY = "";
private static final String EQUALS = "=";
public static List<String> oldSplit(String data){
if(data == null){
return null;
}
String[] array = data.split(COMMA);
List<String> resultList = new ArrayList<>(array.length);
for(String item: array){
if(item != null && !EMPTY.equals(item.trim())){
resultList.add(item.trim());
}
}
return resultList;
}
public static List<String> split(String data){
if(data == null){
return null;
}
// 可以split 到Iterator/List/Stream
// 分隔符可以支持正则表达式
return Splitter.on(COMMA).omitEmptyStrings().trimResults().splitToList(data);
}
public static Map<String,String> oldSplit2Map(String data){
if(data == null){
return null;
}
String[] array = data.split(COMMA);
Map<String,String> resultMap = new HashMap<>(array.length);
for(String item: array){
if(item != null && !EMPTY.equals(item.trim())){
String[] innerArr = item.split(EQUALS);
if(innerArr.length==2) {
resultMap.put(innerArr[0], innerArr[1]);
}
}
}
return resultMap;
}
public static Map<String,String> split2Map(String data){
if(data == null){
return null;
}
// 和joiner相同，可以split 到Map(Beta版本)
return Splitter.on(COMMA).omitEmptyStrings().trimResults().withKeyValueSeparator(EQUALS).split(data);
}
public static void main(String[] args) {
String data = "1,2 , 3, ";
TestUtil.assertIsTrue(TestUtil.equals(split(data), oldSplit(data)), "值不等");
TestUtil.assertIsTrue(TestUtil.equals(split(null), oldSplit(null)), "值不等");
String data2 = "=4,a=1,b=2,c=3,e=5";
TestUtil.assertIsTrue(TestUtil.equals(split2Map(data2), split2Map(data2)), "值不等");
TestUtil.assertIsTrue(TestUtil.equals(split2Map(null), split2Map(null)), "值不等");
}Collection(封装)
public static List<String> oldCreateList(String a, String b, String c){
// m1: java入门的方法
// List<String> resultList = new ArrayList<>();
// resultList.add(a);
// resultList.add(b);
// resultList.add(c);
// return resultList;
// m2: 创建了一个list-Arrays$ArrayList,仅能读取，不支持add/remove操作(java.lang.UnsupportedOperationException)
// return Arrays.asList(a,b,c);
// m3: 包了一层ArrayList，可add/remove，但性能有降低，且很难看
return new ArrayList<>(Arrays.asList(a,b,c));
}
public static List<String> createList(String a, String b, String c){
// 创建一个array list
return Lists.newArrayList(a,b,c);
}
public static List<List<String>> partition(List<String> sourceList, int size){
// 将list按size分块，apache同样提供了ListUtils.partition方法
return Lists.partition(sourceList, size);
}
public static List<Integer> oldTransform(List<String> sourceList){
if(sourceList==null){
return null;
}
// 原生转换
return sourceList.stream().filter(Objects::nonNull).map(String::length).collect(Collectors.toList());
}
public static List<Integer> transform(List<String> sourceList){
if(sourceList==null){
return null;
}
// Lists转换，比起原生代码略短
// 没有找到过滤方法
return Lists.transform(sourceList, s->s==null?null:s.length());
}
public static Map createMap(){
//指定的是实际容量，而非capacity，由于loadFactor默认为0.75，所以new HashMap(16)的实际容量只有12，超出会自动扩容影响效率
return Maps.newHashMapWithExpectedSize(16);
}
public static void main(String[] args){
String a="1",b="2",c="3";
List<String> oldList = oldCreateList(a, b, c);
TestUtil.assertIsTrue(TestUtil.equals(oldCreateList(a, b, c), createList(a,b,c)), "值不等");
oldList.add("12");
System.out.println(partition(oldList, 3));
TestUtil.assertIsTrue(TestUtil.equals(oldTransform(oldList),transform(oldList)),"值不等");
TestUtil.assertIsTrue(TestUtil.equals(oldTransform(null),transform(null)),"值不等");
oldList.add(null);
TestUtil.assertIsTrue(TestUtil.equals(oldTransform(oldList),transform(oldList)),"值不等");
}### 本地缓存()
我们一般会将频繁读取的数据保存在redis等缓存服务中，在每次请求的时候，优先从缓存中读取以减小数据开销，提升性能
* 在访问远程缓存的情况下，一般耗时为3-5ms，虽然这个值不大，但是在一个流程中频繁读取的情况下，也会拖慢系统响应速度，
* 此时我们需要使用本地缓存以提升性能，本地缓存顾名思义即数据存储在本地内存中，适用于频繁读取，并且数据量不太大的场景，在应用重启时本地缓存会全部丢失。
* 而guava提供了一个易用的本地缓存
// fixme:此处为方便测试，设置5秒钟后缓存过期
private static final String CACHE_CONFIG = "initialCapacity=50,maximumSize=1000,expireAfterWrite=5s";
/**
* 以下为guava cache最简单的使用方法
* cachebuilder.from 更便于参数化控制缓存效果
*/
private LoadingCache<String, Optional<Integer>> cacheLoader = CacheBuilder.from(CACHE_CONFIG)
.build(new CacheLoader<String, Optional<Integer>>() {
@Override
public Optional<Integer> load(String key) {
/**
* 在此处初始化缓存，从配置,redis或db从读取
* 备:使用optional的原因是load无法处理空值
*/
return Optional.ofNullable(initCache(key));
}
});
public Integer initCache(String key) {
// fixme:假设加载缓存需要1秒钟
Uninterruptibles.sleepUninterruptibly(1, TimeUnit.SECONDS);
return new Random().nextInt();
}
public static void main(String[] args) throws ExecutionException, InterruptedException {
Stopwatch stopwatch = Stopwatch.createStarted();
String key1 = "paramA";
Caches caches = new Caches();
Optional<Integer> val = caches.cacheLoader.get(key1);
System.out.println(String.format("key:%s,val:%s,time cost:%s", key1, val.get(), stopwatch.elapsed(TimeUnit.MILLISECONDS)));
stopwatch.reset();
stopwatch.start();
val = caches.cacheLoader.get(key1);
// 此处读取本地缓存，加载时间为0
System.out.println(String.format("key:%s,val:%s,time cost:%s", key1, val.get(), stopwatch.elapsed(TimeUnit.MILLISECONDS)));
stopwatch.reset();
stopwatch.start();
String key2 = "paramB";
val = caches.cacheLoader.get(key2);
System.out.println(String.format("key:%s,val:%s,time cost:%s", key2, val.get(), stopwatch.elapsed(TimeUnit.MILLISECONDS)));
stopwatch.reset();
// Uninterruptibles.sleepUninterruptibly(5, TimeUnit.SECONDS);
// 手动清除本地缓存
caches.cacheLoader.invalidateAll();
System.out.println("size:"+caches.cacheLoader.asMap().size());
stopwatch.start();
val = caches.cacheLoader.get(key1);
// 此时耗时为1秒
System.out.println(String.format("key:%s,val:%s,time cost:%s", key1, val.get(), stopwatch.elapsed(TimeUnit.MILLISECONDS)));
}基础类型
基础类型的封装:Booleans/Bytes/Chars/Doubles/Floats/Ints/Longs/Shorts八种基本类型的封装和衍生类型
* 原生类型数组转化为list
* 校验:checkedCast,ensureCapacity
* 比较:compare,min,max
* 查找:contains,indexOf,lastIndexOf
* 类型转换:toByteArray,fromByteArray,fromBytes,stringConverter,toArray,asList,tryParse
* 合并:concat,join,
* 排序:sortDescending,reverse