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在 Java 中如何保存和加載文件中的數據 - 用於文件 I/O 讀寫操作的簡單生產就緒實用程序

已發表: 2020-10-11
在 Java 中如何保存和加載文件中的數據 - 用於文件 I:O 讀寫操作的簡單生產就緒實用程序

如何將對象寫入文件並將其讀回？

Java 的 API 非常驚人，而在 Java 8 中，我們完全啟用了更多的 API，例如 Lambda、方法引用、默認方法、更好的類型接口、重複註釋、方法參數反射等等。

前段時間我寫了一篇關於如何在 Java 中從文件中讀取 JSON 對象的文章。 這是簡單的java讀取操作。 但在本教程中，我們將使用簡單的 Production Ready Java Utility 從文件中save and load數據。

用於文件讀取：寫入操作的簡單生產就緒實用程序

我們不僅保存簡單的對象，還將創建 CrunchifyCompany 類型的簡單 Java POJO，並使用GSON保存和檢索對象。 您需要以下依賴項才能運行以下程序。

將依賴項放在您的 Maven 項目中。 如果您有動態 Web 項目並希望將其轉換為 Maven 項目，請按照以下步驟操作。

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< dependency >
< groupId > com . google . code . gson < / groupId >
< artifactId > gson < / artifactId >
< version > 2.3 < / version >
< / dependency >

這是一個流程：

  • 創建類CrunchifyReadWriteUtilityForFile.java
  • 創建具有兩個字段的私有內部類CrunchifyCompany
    • 私人內部employees ；
    • 私人字符串companyName ；
  • 在 main 方法中創建對象crunchify
  • 將對象轉換為Gson ，以便將其保存到文件中
  • 使用方法crunchifyWriteToFile將數據保存到 Java 中的文件
  • 使用方法crunchifyReadFromFile從 Java 文件中檢索數據

這是一個完整的例子：

Java
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package crunchify . com . tutorial ;
 
import com . google . gson . Gson ;
import com . google . gson . stream . JsonReader ;
 
import java . io . * ;
import java . nio . charset . StandardCharsets ;
 
/**
* @author Crunchify.com
* Best and simple Production ready utility to save/load
* (read/write) data from/to file
*/
 
public class CrunchifyReadWriteUtilityForFile {
private static final String crunchifyFileLocation = "/Users/appshah/Documents/crunchify.txt" ;
private static final Gson gson = new Gson ( ) ;
// CrunchifyComapny Class with two fields
// - Employees
// - CompanyName
private static class CrunchifyCompany {
private int employees ;
private String companyName ;
public int getEmployees ( ) {
return employees ;
}
public void setEmployees ( int employees ) {
this . employees = employees ;
}
public String getCompanyName ( ) {
return companyName ;
}
public void setCompanyName ( String companyName ) {
this . companyName = companyName ;
}
}
// Main Method
public static void main ( String [ ] args ) {
CrunchifyCompany crunchify = new CrunchifyCompany ( ) ;
crunchify . setCompanyName ( "Crunchify.com" ) ;
crunchify . setEmployees ( 4 ) ;
// Save data to file
crunchifyWriteToFile ( gson . toJson ( crunchify ) ) ;
// Retrieve data from file
crunchifyReadFromFile ( ) ;
}
// Save to file Utility
private static void crunchifyWriteToFile ( String myData ) {
File crunchifyFile = new File ( crunchifyFileLocation ) ;
// exists(): Tests whether the file or directory denoted by this abstract pathname exists.
if ( ! crunchifyFile . exists ( ) ) {
try {
File directory = new File ( crunchifyFile . getParent ( ) ) ;
if ( ! directory . exists ( ) ) {
// mkdirs(): Creates the directory named by this abstract pathname, including any necessary but nonexistent parent directories.
// Note that if this operation fails it may have succeeded in creating some of the necessary parent directories.
directory . mkdirs ( ) ;
}
// createNewFile(): Atomically creates a new, empty file named by this abstract pathname if and only if a file with this name does not yet exist.
// The check for the existence of the file and the creation of the file if it does not exist are a single operation
// that is atomic with respect to all other filesystem activities that might affect the file.
crunchifyFile . createNewFile ( ) ;
} catch ( IOException e ) {
crunchifyLog ( "Exception Occurred: " + e . toString ( ) ) ;
}
}
try {
// Convenience class for writing character files
FileWriter crunchifyWriter ;
crunchifyWriter = new FileWriter ( crunchifyFile . getAbsoluteFile ( ) , true ) ;
// Writes text to a character-output stream
BufferedWriter bufferWriter = new BufferedWriter ( crunchifyWriter ) ;
bufferWriter . write ( myData . toString ( ) ) ;
bufferWriter . close ( ) ;
crunchifyLog ( "Company data saved at file location: " + crunchifyFileLocation + " Data: " + myData + "\n" ) ;
} catch ( IOException e ) {
crunchifyLog ( "Hmm.. Got an error while saving Company data to file " + e . toString ( ) ) ;
}
}
// Read From File Utility
public static void crunchifyReadFromFile ( ) {
// File: An abstract representation of file and directory pathnames.
// User interfaces and operating systems use system-dependent pathname strings to name files and directories.
File crunchifyFile = new File ( crunchifyFileLocation ) ;
if ( ! crunchifyFile . exists ( ) )
crunchifyLog ( "File doesn't exist" ) ;
InputStreamReader isReader ;
try {
isReader = new InputStreamReader ( new FileInputStream ( crunchifyFile ) , StandardCharsets . UTF_8 ) ;
JsonReader myReader = new JsonReader ( isReader ) ;
CrunchifyCompany company = gson . fromJson ( myReader , CrunchifyCompany . class ) ;
crunchifyLog ( "Company Name: " + company . getCompanyName ( ) ) ;
int employee = company . getEmployees ( ) ;
crunchifyLog ( "# of Employees: " + Integer . toString ( employee ) ) ;
} catch ( Exception e ) {
crunchifyLog ( "error load cache from file " + e . toString ( ) ) ;
}
crunchifyLog ( "\nCompany Data loaded successfully from file " + crunchifyFileLocation ) ;
}
private static void crunchifyLog ( String string ) {
System . out . println ( string ) ;
}
}

Eclipse 控制台輸出：

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Company data saved at file location : / Users / appshah / Documents / crunchify . txt Data : { "employees" : 4 , "companyName" : "Crunchify.com" }
 
Company Name : Crunchify . com
# of Employees: 4
 
Company Data loaded successfully from file / Users / appshah / Documents / crunchify . txt

這是一個 crunchify.txt 文件內容。

當我運行程序two times時，您會在這裡看到兩次 JSONObject，因為我們將值附加到crunchify.txt文件。

如何在 Java 中將對象保存到文件 - Crunchify