缓存List并写入文件持久化

LIfe is half spent before we know what is it.

缓存List并写入文件持久化

需要缓存一个List集合，比如缓存一个输入框中用户之前输入过的内容，下次当用户再想往输入框中写东西就调用这个缓存的接口，把之前输入过的东西从缓存中取出并返回；

而为了这么一个小小的缓存，引入第三方库Redis或是Cache等也不太划算，于是就可以把缓存写入文件中，序列化到Java虚拟机中，这样就可以支持持久化，即使重启项目缓存的List依然存在；

缓存工具类：

 package com.xinyan.springcloud.tjt;

 import java.io.File;
 import java.io.FileInputStream;
 import java.io.FileOutputStream;
 import java.io.IOException;
 import java.io.ObjectInputStream;
 import java.io.ObjectOutputStream;
 import java.io.Serializable;
 import java.util.Arrays;
 import java.util.List;

 public class StreamUtils implements Serializable{
     private static final long serialVersionUID = 1L;
     /**
      * 序列化,List
      * @param list
      * @param file
      * @param <T>
      * @return
      */
     public static  <T> boolean writeObject(List<T> list,File file)
     {
         T[] array = (T[]) list.toArray();
         try(ObjectOutputStream out = new ObjectOutputStream(new FileOutputStream(file)))
         {
             out.writeObject(array);
             out.flush();
             return true;
         }
         catch (IOException e)
         {
             e.printStackTrace();
             return false;
         }
     }

     /**
      * 反序列化,List
      * @param file
      * @param <E>
      * @return
      */
     public static <E> List<E> readObjectForList(File file)
     {
         E[] object;
         try(ObjectInputStream out = new ObjectInputStream(new FileInputStream(file)))
         {
             object = (E[]) out.readObject();
             return Arrays.asList(object);
         }
         catch (IOException e)
         {
             e.printStackTrace();
         }
         catch (ClassNotFoundException e)
         {
             e.printStackTrace();
         }
         return null;
     }

 }

测试缓存结果：

 package com.xinyan.springcloud.tjt;

 import java.io.File;
 import java.util.ArrayList;
 import java.util.List;

 import lombok.extern.log4j.Log4j;

 @Log4j
 public class TestStreamUtils {

     private final static List<String> listSave = new ArrayList<>();
     private final static String  FILE_CACHE = "file-tjt";

     public static void main(String[] args) throws Exception {
         TestStreamUtils.saveListToJvm("admin");
         TestStreamUtils.saveListToJvm("user");
         TestStreamUtils.saveListToJvm("LieIWantTo");
         Object listFromJvm = TestStreamUtils.getListFromJvm();
         System.out.println("listFromJvm:"+listFromJvm);
     }

     public static void saveListToJvm(String input) throws Exception{
         List<String> listInput = new ArrayList<>();
         listSave.add(input);
         listInput.addAll(listSave);
         boolean writeObject = StreamUtils.writeObject(listInput, new File(FILE_CACHE));
         if (!writeObject) {
             log.info("saveListToJvm failed!");
         }
     }

     public static Object getListFromJvm() {
         File file = new File(FILE_CACHE);
         List<Object> readObjectForList = null;
         if (file.exists()) {
              readObjectForList = StreamUtils.readObjectForList(file);
              if (readObjectForList.size() >20) {
                 readObjectForList.remove(0);
             }
         }else {
             log.info("file not exist!");
         }
         return readObjectForList;
     }

 }

测试结果如下图：