连接池：关闭还是不关闭连接？

Question

I'm using dbcp's BasicDataSource in my JSF Java application. Since the basic convention is to close the connection after using it, I do so in catch - finally in my code. However, the application grinds to a halt with the error,

java.sql.SQLException: Connection is null.
at org.apache.tomcat.dbcp.dbcp2.DelegatingConnection.checkOpen(DelegatingConnection.java:611)
at org.apache.tomcat.dbcp.dbcp2.DelegatingConnection.createStatement(DelegatingConnection.java:258)

So I decide to not close my connections; my code almost runs okay, but then often stops with this error:

Caused by: org.postgresql.util.PSQLException: FATAL: remaining connection slots are reserved for non-replication superuser connections

Below is my connection configuration:

public class StageDB {
    public StageDB() {}
    public static Connection getConnection() {
        BasicDataSource ds = new BasicDataSource();
        ds.setDriverClassName(JDBC_DRIVER);
        ds.setUsername(USER);
        ds.setPassword(PASS);
        ds.setUrl(DB_URL);
        ds.setTimeBetweenEvictionRunsMillis(20*1000);
        ds.setMinIdle(0);
        ds.setMaxIdle(10);
        ds.setMaxOpenPreparedStatements(100);
        conn = ds.getConnection();
        return conn;
    }
}

I should mention I've tried playing around with these settings, and also using defaults, but with the same results. What could I be doing wrong?

Answer 1

I found the solution to this after I realized that I was doing it all wrong. So here is what I was able to come up with, that works perfectly with my design approach.

//1. Create pooled connections datasource class using the Singleton.

/***************************
* This is the pooled datasource class
****************************/
public class PrimaryDS {
    private PrimaryDS primaryDS;

    public PrimaryDS() {
        ds = new BasicDataSource();
        ds.setDriverClassName(JDBC_DRIVER);
        ds.setUsername(USER);
        ds.setPassword(PASS);
        ds.setUrl(DB_URL);
    }

    public static PrimaryDS getInstance() {
        primaryDS = primaryDS == null ? new PrimaryDS() : primaryDS;
        return primaryDS;
    }

    public BasicDataSource getDataSource() {
        return ds;
    }

    public void setDataSource(BasicDataSource ds) {
        this.ds = ds;
    }
}

//2. DAOs make call to the datasource. Initialize DS in the DAO's constructor.

/***************************
* This is in the DAO's constructor
****************************/
ds = PrimaryDS.getInstance().getDataSource();

//3. DAOs have the database manupulation methods. In each of these methods, 
//create connection object from ds, and ensure it's closed in the catch - finally.

/***************************
* This is inside one of the DAO methods
****************************/
try {
    conn = ds.getConnection();
    stmt = null;
    rs = null;
    PreparedStatement pstmt = conn.prepareStatement(ACTIVE_ACCOUNTS_SQL);
    pstmt.setByte(1,status);
    ResultSet rs = pstmt.executeQuery();
    // TODO loop through rs
} catch (SQLException e) {
    e.printStackTrace();
} finally {
    try {
        if(rs != null) rs.close();
        if(stmt != null) stmt.close();
        if(conn != null) conn.close();
    } catch (Exception e) {
        e.printStackTrace();
    }
}