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Exemple try-with-resources dans JDK 7

Exemple d'essai avec les ressources Java 7

Avant Java 7, nous pouvons fermer une ressource avecfinally: 

    try{
        //open resources
    }catch(Exception){
        //handle exception
    }finally{
        //close resources
    }

Dans Java 7, une nouvelle approchetry-with-resources est introduite, elle permet de fermer automatiquement les ressources. 

    try(open resources, one or more resources){
        //...
    }
    //after try block, the resource will be closed automatically.

1. BufferedReader

1.1 Before Java 7, we have to close the BufferedReader manually.

package com.example.io;

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;

public class TestApp {

    public static void main(String[] args) {

        BufferedReader br = null;
        String line;

        try {

            br = new BufferedReader(new FileReader("C:\\testing.txt"));
            while ((line = br.readLine()) != null) {
                System.out.println(line);
            }

        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                if (br != null) br.close();
            } catch (IOException ex) {
                ex.printStackTrace();
            }
        }

    }

}

1.2 In Java 7, with try-with-resources, the BufferedReader will be closed automatically after try block.

package com.example.io;

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;

public class TestApp {

    public static void main(String[] args) {

        String line;

        try (BufferedReader br = new BufferedReader(
                new FileReader("C:\\testing.txt"))) {

            while ((line = br.readLine()) != null) {
                System.out.println(line);
            }

        } catch (IOException e) {
            e.printStackTrace();
        }

        // br will be closed automatically
    }

}

2. JDBC

Exemple Java pour fermer automatiquement 2 ressources dans une instruction try-with-resources.

2.1 Before Java 7

    @Override
    public void update(int postId, String metaValue) {

        Connection connection = null;
        PreparedStatement ps = null;

        try {
            connection = dataSource.getConnection();
            ps = connection.prepareStatement(SQL_UPDATE_POST_META);

            ps.setString(1, metaValue);
            ps.setInt(2, postId);
            ps.setString(3, GlobalUtils.META_KEY);

            ps.executeUpdate();

        } catch (Exception e) {
            //
        } finally {

            if (ps != null) {
                ps.close();
            }

            if (connection != null) {
                connection.close();
            }
        }

    }

2.2 Java 7 try-with-resources

    @Override
    public void update(int postId, String metaValue) {

        try (Connection connection = dataSource.getConnection();
             PreparedStatement ps = connection.prepareStatement(SQL_UPDATE_POST_META)) {
            ps.setString(1, metaValue);
            ps.setInt(2, postId);
            ps.setString(3, GlobalUtils.META_KEY);

            ps.executeUpdate()

        } catch (Exception e) {
            //...
        }

    }

Références

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