java.sql.Connectionプロキシの素

```java
import java.sql.Array;
import java.sql.Blob;
import java.sql.CallableStatement;
import java.sql.Clob;
import java.sql.Connection;
import java.sql.DatabaseMetaData;
import java.sql.NClob;
import java.sql.PreparedStatement;
import java.sql.SQLClientInfoException;
import java.sql.SQLException;
import java.sql.SQLWarning;
import java.sql.SQLXML;
import java.sql.Savepoint;
import java.sql.Statement;
import java.sql.Struct;
import java.util.Map;
import java.util.Properties;
import java.util.concurrent.Executor;

/** java.sql.Connectionプロキシの素 */
public abstract class ProxyConnectionBase implements Connection {
    protected Connection conn;
    public ProxyConnectionBase(Connection conn){
        this.conn = conn;
    }

    /** {@inheritDoc} */
    @Override
    @SuppressWarnings("unchecked")
    public final <T> T unwrap(Class<T> iface) throws SQLException {
        if (iface.isInstance(conn)) {
            return (T) conn;
        } else {
        	throw new SQLException("`" + iface + "`へキャストできないようです.");
        }
    }

    /** {@inheritDoc} */
    @Override
    public final boolean isWrapperFor(Class<?> iface) throws SQLException {
        return iface.isInstance(conn);
    }

    /** {@inheritDoc} */
    @Override
    public Statement createStatement() throws SQLException {
        return conn.createStatement();
    }

    /** {@inheritDoc} */
    @Override
    public PreparedStatement prepareStatement(String sql) throws SQLException {
        return conn.prepareStatement(sql);
    }

    /** {@inheritDoc} */
    @Override
    public CallableStatement prepareCall(String sql) throws SQLException {
        return conn.prepareCall(sql);
    }

    /** {@inheritDoc} */
    @Override
    public String nativeSQL(String sql) throws SQLException {
        return conn.nativeSQL(sql);
    }

    /** {@inheritDoc} */
    @Override
    public void setAutoCommit(boolean autoCommit) throws SQLException {
        conn.setAutoCommit(autoCommit);
    }

    /** {@inheritDoc} */
    @Override
    public boolean getAutoCommit() throws SQLException {
        return conn.getAutoCommit();
    }

    /** {@inheritDoc} */
    @Override
    public void commit() throws SQLException {
        conn.commit();
    }

    /** {@inheritDoc} */
    @Override
    public void rollback() throws SQLException {
        conn.rollback();
    }

    /** {@inheritDoc} */
    @Override
    public void close() throws SQLException {
        conn.close();
    }

    /** {@inheritDoc} */
    @Override
    public boolean isClosed() throws SQLException {
        return conn.isClosed();
    }

    /** {@inheritDoc} */
    @Override
    public DatabaseMetaData getMetaData() throws SQLException {
        return conn.getMetaData();
    }

    /** {@inheritDoc} */
    @Override
    public void setReadOnly(boolean readOnly) throws SQLException {
        conn.setReadOnly(readOnly);
    }

    /** {@inheritDoc} */
    @Override
    public boolean isReadOnly() throws SQLException {
        return conn.isReadOnly();
    }

    /** {@inheritDoc} */
    @Override
    public void setCatalog(String catalog) throws SQLException {
        conn.setCatalog(catalog);
    }

    /** {@inheritDoc} */
    @Override
    public String getCatalog() throws SQLException {
        return conn.getCatalog();
    }

    /** {@inheritDoc} */
    @Override
    public void setTransactionIsolation(int level) throws SQLException {
        conn.setTransactionIsolation(level);
    }

    /** {@inheritDoc} */
    @Override
    public int getTransactionIsolation() throws SQLException {
        return conn.getTransactionIsolation();
    }

    /** {@inheritDoc} */
    @Override
    public SQLWarning getWarnings() throws SQLException {
        return conn.getWarnings();
    }

    /** {@inheritDoc} */
    @Override
    public void clearWarnings() throws SQLException {
        conn.clearWarnings();
    }

    /** {@inheritDoc} */
    @Override
    public Statement createStatement(int resultSetType, int resultSetConcurrency) throws SQLException {
        return conn.createStatement(resultSetType, resultSetConcurrency);
    }

    /** {@inheritDoc} */
    @Override
    public PreparedStatement prepareStatement(String sql, int resultSetType, int resultSetConcurrency)
            throws SQLException {
        return conn.prepareStatement(sql, resultSetType, resultSetConcurrency);
    }

    /** {@inheritDoc} */
    @Override
    public CallableStatement prepareCall(String sql, int resultSetType, int resultSetConcurrency) throws SQLException {
        return conn.prepareCall(sql, resultSetType, resultSetConcurrency);
    }

    /** {@inheritDoc} */
    @Override
    public Map<String, Class<?>> getTypeMap() throws SQLException {
        return conn.getTypeMap();
    }

    /** {@inheritDoc} */
    @Override
    public void setTypeMap(Map<String, Class<?>> map) throws SQLException {
        conn.setTypeMap(map);
    }

    /** {@inheritDoc} */
    @Override
    public void setHoldability(int holdability) throws SQLException {
        conn.setHoldability(holdability);
    }

    /** {@inheritDoc} */
    @Override
    public int getHoldability() throws SQLException {
        return conn.getHoldability();
    }

    /** {@inheritDoc} */
    @Override
    public Savepoint setSavepoint() throws SQLException {
        return conn.setSavepoint();
    }

    /** {@inheritDoc} */
    @Override
    public Savepoint setSavepoint(String name) throws SQLException {
        return conn.setSavepoint(name);
    }

    /** {@inheritDoc} */
    @Override
    public void rollback(Savepoint savepoint) throws SQLException {
        conn.rollback(savepoint);
    }

    /** {@inheritDoc} */
    @Override
    public void releaseSavepoint(Savepoint savepoint) throws SQLException {
        conn.releaseSavepoint(savepoint);
    }

    /** {@inheritDoc} */
    @Override
    public Statement createStatement(int resultSetType, int resultSetConcurrency, int resultSetHoldability)
            throws SQLException {
        return conn.createStatement(resultSetType, resultSetConcurrency, resultSetHoldability);
    }

    /** {@inheritDoc} */
    @Override
    public PreparedStatement prepareStatement(String sql, int resultSetType, int resultSetConcurrency,
            int resultSetHoldability) throws SQLException {
        return conn.prepareStatement(sql, resultSetType, resultSetConcurrency, resultSetHoldability);
    }

    /** {@inheritDoc} */
    @Override
    public CallableStatement prepareCall(String sql, int resultSetType, int resultSetConcurrency,
            int resultSetHoldability) throws SQLException {
        return conn.prepareCall(sql, resultSetType, resultSetConcurrency, resultSetHoldability);
    }

    /** {@inheritDoc} */
    @Override
    public PreparedStatement prepareStatement(String sql, int autoGeneratedKeys) throws SQLException {
        return conn.prepareStatement(sql, autoGeneratedKeys);
    }

    /** {@inheritDoc} */
    @Override
    public PreparedStatement prepareStatement(String sql, int[] columnIndexes) throws SQLException {
        return conn.prepareStatement(sql, columnIndexes);
    }

    /** {@inheritDoc} */
    @Override
    public PreparedStatement prepareStatement(String sql, String[] columnNames) throws SQLException {
        return conn.prepareStatement(sql, columnNames);
    }

    /** {@inheritDoc} */
    @Override
    public Clob createClob() throws SQLException {
        return conn.createClob();
    }

    /** {@inheritDoc} */
    @Override
    public Blob createBlob() throws SQLException {
        return conn.createBlob();
    }

    /** {@inheritDoc} */
    @Override
    public NClob createNClob() throws SQLException {
        return conn.createNClob();
    }

    /** {@inheritDoc} */
    @Override
    public SQLXML createSQLXML() throws SQLException {
        return conn.createSQLXML();
    }

    /** {@inheritDoc} */
    @Override
    public boolean isValid(int timeout) throws SQLException {
        return conn.isValid(timeout);
    }

    /** {@inheritDoc} */
    @Override
    public void setClientInfo(String name, String value) throws SQLClientInfoException {
        conn.setClientInfo(name, value);
    }

    /** {@inheritDoc} */
    @Override
    public void setClientInfo(Properties properties) throws SQLClientInfoException {
        conn.setClientInfo(properties);
    }

    /** {@inheritDoc} */
    @Override
    public String getClientInfo(String name) throws SQLException {
        return conn.getClientInfo(name);
    }

    /** {@inheritDoc} */
    @Override
    public Properties getClientInfo() throws SQLException {
        return conn.getClientInfo();
    }

    /** {@inheritDoc} */
    @Override
    public Array createArrayOf(String typeName, Object[] elements) throws SQLException {
        return conn.createArrayOf(typeName, elements);
    }

    /** {@inheritDoc} */
    @Override
    public Struct createStruct(String typeName, Object[] attributes) throws SQLException {
        return conn.createStruct(typeName, attributes);
    }

    /** {@inheritDoc} */
    @Override
    public void setSchema(String schema) throws SQLException {
        conn.setSchema(schema);
    }

    /** {@inheritDoc} */
    @Override
    public String getSchema() throws SQLException {
        return conn.getSchema();
    }

    /** {@inheritDoc} */
    @Override
    public void abort(Executor executor) throws SQLException {
        conn.abort(executor);
    }

    /** {@inheritDoc} */
    @Override
    public void setNetworkTimeout(Executor executor, int milliseconds) throws SQLException {
        conn.setNetworkTimeout(executor, milliseconds);
    }

    /** {@inheritDoc} */
    @Override
    public int getNetworkTimeout() throws SQLException {
        return conn.getNetworkTimeout();
    }
}
```

# え？なにこれ？？？

と、思われたかもしれませんが、便利ですよ。これ。
みなさん、使い道を予想してみてください。

# というかタイトルにプロキシって書いてあるじゃん

そうです。プロキシを簡単に作れる「プロキシの素」シリーズです。
それでは`java.sql.Connection#prepareStatement`でもらったsqlを
コンソールに出力するプロキシを作ってみましょう。

```java
/** SQLをコンソールに出力するプロキシ */
public class ProxyConnection extends ProxyConnectionBase{
	public ProxyConnection(Connection arg0) {
		super(arg0);
	}
    /** {@inheritDoc} */
    @Override
    public PreparedStatement prepareStatement(String sql) throws SQLException {
    	System.out.println(sql);
        return conn.prepareStatement(sql);
    }
}
```

簡単ですね！
あとは`java.sql.Connection connection = new ProxyConnection(connection);`
とラップするだけで使えるようになります。

ちなみに以下の記事のように`java.lang.reflect.Proxy`を使って、
プログラムチックにプロキシを作ることもできます。
[SQLやSQL結果をログに出すためのプロキシ \- Qiita](https://qiita.com/momosetkn/items/c0bc1d30b995bfd55fc3)