java基础类库学习 java.sql（2）常用的数据库接口

本文链接：https://blog.youkuaiyun.com/strivenoend/article/details/83661503

本文聚焦于Java基础类库中的java.sql包，详细阐述了 JDBC 接口的关键角色，包括Driver接口（数据库驱动）、DriverManager（驱动管理）、Connection（数据库连接）以及Statement和PreparedStatement（SQL语句执行）。PreparedStatement作为Statement的子接口，因其预编译特性而具备更好的性能。ResultSet接口则用于承载执行SQL后返回的数据。

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下面仔细的学习下jdbc接口吧

在java.sql包中定义了jdbc接口的各个类

Driver：驱动接口

public interface Driver {

Connection connect(String url, java.util.Properties info)
    throws SQLException;

boolean acceptsURL(String url) throws SQLException;

DriverPropertyInfo[] getPropertyInfo(String url, java.util.Properties info)
                     throws SQLException;

int getMinorVersion();

}

DriverManager:。用于管理驱动的类

public class DriverManager {

private DriverManager(){}

static {
    loadInitialDrivers();
    println("JDBC DriverManager initialized");
}

@CallerSensitive获取数据库连接对象
public static Connection getConnection(String url,
    String user, String password) throws SQLException {
    java.util.Properties info = new java.util.Properties();

    if (user != null) {
        info.put("user", user);
    }
    if (password != null) {
        info.put("password", password);
    }

    return (getConnection(url, info, Reflection.getCallerClass()));
}

Connection：数据库连接的接口，用于管理数据库连接的接口，由各大数据库厂商去提供数据库连接的实现

public interface Connection  extends Wrapper, AutoCloseable {

Statement createStatement() throws SQLException;

PreparedStatement prepareStatement(String sql)
    throws SQLException;

CallableStatement prepareCall(String sql) throws SQLException;

String nativeSQL(String sql) throws SQLException;

boolean getAutoCommit() throws SQLException;

void rollback() throws SQLException;

void close() throws SQLException;

Savepoint setSavepoint(String name) throws SQLException;

Clob createClob() throws SQLException;

void setNetworkTimeout(Executor executor, int milliseconds) throws SQLException;

void setNetworkTimeout(Executor executor, int milliseconds) throws SQLException;

}

Statement：执行sql语句的接口，由各大数据库厂商去提供实现类

public interface Statement extends Wrapper, AutoCloseable {

ResultSet executeQuery(String sql) throws SQLException;

int executeUpdate(String sql) throws SQLException;

void close() throws SQLException;

void setCursorName(String name) throws SQLException;

boolean execute(String sql) throws SQLException;

ResultSet getResultSet() throws SQLException;

int getUpdateCount() throws SQLException;

Connection getConnection()  throws SQLException;

}

preparedStatement:预编译的执行sql语句的接口，由各大数据库厂商去提供实现类，是Statement的子接口

允许数据库预编译sql语句，以后每次只改变sql命令的参数，避免数据库每次都需要编译sql语句，因此性能更好

因此使用preparredStatement执行sql时，无需在传入sql语句，只要为预编译的sql语句传入参数即可

public interface PreparedStatement extends Statement {

ResultSet executeQuery() throws SQLException;

int executeUpdate() throws SQLException;

void setTimestamp(int parameterIndex, java.sql.Timestamp x)
        throws SQLException;

void clearParameters() throws SQLException;

boolean execute() throws SQLException;

void setArray (int parameterIndex, Array x) throws SQLException;

void setDate(int parameterIndex, java.sql.Date x, Calendar cal)
        throws SQLException;

void setTime(int parameterIndex, java.sql.Time x, Calendar cal)
        throws SQLException;

void setNString(int parameterIndex, String value) throws SQLException;

void setClob(int parameterIndex, Reader reader)
  throws SQLException;

}

ResultSet结果集类的接口，由各大数据库厂商去提供实现

public interface ResultSet extends Wrapper, AutoCloseable {

boolean next() throws SQLException;

void close() throws SQLException;

String getString(int columnIndex) throws SQLException;

boolean getBoolean(int columnIndex) throws SQLException;

java.io.InputStream getBinaryStream(int columnIndex)
    throws SQLException;

Blob getBlob(String columnLabel) throws SQLException;

}