swift3.0网络图片缓存原理简析

 //存储图片的文件夹
 var ljFilePath:String =NSHomeDirectory() +"/Documents/"+"LJImageCache/"

#ifndef bridge_h 
#define bridge_h 
 
#import <CommonCrypto/CommonDigest.h> 
 
#endif /* bridge_h */ 

import Foundation 
 
extension String { 
  var md5 : String{ 
    let str = self.cString(using: String.Encoding.utf8) 
    let strLen = CC_LONG(self.lengthOfBytes(using: String.Encoding.utf8)) 
    let digestLen = Int(CC_MD5_DIGEST_LENGTH) 
    let result = UnsafeMutablePointer<CUnsignedChar>.allocate(capacity: digestLen) 
     
    CC_MD5(str!, strLen, result) 
     
    let hash = NSMutableString() 
    for i in 0 ..< digestLen { 
      hash.appendFormat("%02x", result[i]) 
    } 
    result.deinitialize() 
     
    return String(format: hash as String) 
  } 
} 

func urlSession(_ session: URLSession, task: URLSessionTask, didCompleteWithError error: Error?) 
  { 
    if ljcallBackClosure != nil ,let data = self.responseData{ 
      weak var weakSelf : LJOpreationManager? = self 
      DispatchQueue.main.async 
      { 
        print("URLSessionDataDelegate----数据下载完毕") 
         
        LJCacheDataManage.shared.setMemoryCache((task.currentRequest?.url?.absoluteString)!,data as Data) 
         
        //图片缓存，根据唯一的url来作为存储数据的名称 
        let a = LJFileManager.shared.writeFile((task.currentRequest?.url?.absoluteString)!,data as NSData) 
         
        print("-----写入文件成功\(a)") 
         
        //将接收的数据结果回调到前台，用于进度展示 
        weakSelf?.ljcallBackClosure!(data as Data ,nil) 
      } 
    } 
  } 

public func retrieveImage(_ ljurl: String, _ ljcallback: @escaping OpreationClosure){ 
     
    if ljurl != "" { 
       
      if LJFileManager.shared.readFileFromCache(ljurl) != nil { 
        //将接收的数据结果回调到前台，用于进度展示 
        print("获取的是Disk缓存数据哦完毕") 
        ljcallback(LJFileManager.shared.readFileFromCache(ljurl) as! Data,nil) 
      } 
      //首先取缓存数据，没取到的话，直接下载 
     else if LJCacheDataManage.shared.getMemoryCache(ljurl) != nil { 
        //将接收的数据结果回调到前台，用于进度展示 
        print("获取的是Memory缓存数据哦完毕") 
        ljcallback(LJCacheDataManage.shared.getMemoryCache(ljurl) ,nil) 
      } 
      else 
      { 
       _ = self.requestWebByUrl(ljurl, ljcallback) 
      } 
    } 
  } 

/* 写文件 
  fileName: 文件名称 
  data: 数据data 
*/ 
func writeFile(_ fileName:String , _ data:NSData) -> Bool{ 
   
  //let filePath:String = NSHomeDirectory() + "/Documents/" + fileName.md5 
  //return data.write(toFile: filePath, atomically: true) 
  guard self.isExistFileDir(ljFilePath) else{ 
    return false 
  } 
   
  guard let filePath : String = ljFilePath + fileName.md5 else{ 
    return false 
  } 
  return data.write(toFile: filePath, atomically: true) 
} 
 
//读取文件 -（根据路径） 
func readFileFromCache(_ path:String) -> NSData?{ 
   
  if self.isExistFileDir(ljFilePath) 
  { 
    let ljpatch = ljFilePath + path.md5 
    var result:NSData? 
    do{ 
      result = try NSData(contentsOfFile: ljpatch, options: Data.ReadingOptions.uncached) 
    }catch{ 
      return nil 
    } 
    return result 
  } 
  return nil 
} 

import Foundation 
 
class LJCacheDataManage: NSObject{ 
   
  //单例 
  public static let shared = LJCacheDataManage() 
   
  // public var diskCache = 
   
  //缓存的数据 
  public var memoryCache = Dictionary<String, Data>() 
   
  //返回缓存的数据 
  func getMemoryCache(_ urlStr : String) -> Data? { 
     
    print("返回缓存的数据------\(memoryCache[urlStr] ?? nil)") 
    return (memoryCache[urlStr] ?? nil) 
  } 
   
  //设置缓存值 
  func setMemoryCache(_ urlStr : String, _ data : Data){ 
    if urlStr != "", data != nil { 
      memoryCache[urlStr] = data 
    } 
  } 
}