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本文次要钻研一下如何获取PreparedStatement的参数
PreparedStatement
java/sql/PreparedStatement.java
public interface PreparedStatement extends Statement { void setNull(int parameterIndex, int sqlType) throws SQLException; void setBoolean(int parameterIndex, boolean x) throws SQLException; void setInt(int parameterIndex, int x) throws SQLException; void setLong(int parameterIndex, long x) throws SQLException; //...... default void setObject(int parameterIndex, Object x, SQLType targetSqlType, int scaleOrLength) throws SQLException { throw new SQLFeatureNotSupportedException("setObject not implemented"); } default void setObject(int parameterIndex, Object x, SQLType targetSqlType) throws SQLException { throw new SQLFeatureNotSupportedException("setObject not implemented"); } /** * Retrieves the number, types and properties of this * <code>PreparedStatement</code> object's parameters. * * @return a <code>ParameterMetaData</code> object that contains information * about the number, types and properties for each * parameter marker of this <code>PreparedStatement</code> object * @exception SQLException if a database access error occurs or * this method is called on a closed <code>PreparedStatement</code> * @see ParameterMetaData * @since 1.4 */ ParameterMetaData getParameterMetaData() throws SQLException;}PreparedStatement继承了Statement接口，它次要是多定义了一系列的set办法，然而没有定义get办法，只是定义了getParameterMetaData办法返回ParameterMetaData
ParameterMetaData
java/sql/ParameterMetaData.java
public interface ParameterMetaData extends Wrapper { /** * Retrieves the number of parameters in the <code>PreparedStatement</code> * object for which this <code>ParameterMetaData</code> object contains * information. * * @return the number of parameters * @exception SQLException if a database access error occurs * @since 1.4 */ int getParameterCount() throws SQLException; /** * Retrieves whether null values are allowed in the designated parameter. * * @param param the first parameter is 1, the second is 2, ... * @return the nullability status of the given parameter; one of * <code>ParameterMetaData.parameterNoNulls</code>, * <code>ParameterMetaData.parameterNullable</code>, or * <code>ParameterMetaData.parameterNullableUnknown</code> * @exception SQLException if a database access error occurs * @since 1.4 */ int isNullable(int param) throws SQLException; /** * The constant indicating that a * parameter will not allow <code>NULL</code> values. */ int parameterNoNulls = 0; /** * The constant indicating that a * parameter will allow <code>NULL</code> values. */ int parameterNullable = 1; /** * The constant indicating that the * nullability of a parameter is unknown. */ int parameterNullableUnknown = 2; /** * Retrieves whether values for the designated parameter can be signed numbers. * * @param param the first parameter is 1, the second is 2, ... * @return <code>true</code> if so; <code>false</code> otherwise * @exception SQLException if a database access error occurs * @since 1.4 */ boolean isSigned(int param) throws SQLException; /** * Retrieves the designated parameter's specified column size. * * <P>The returned value represents the maximum column size for the given parameter. * For numeric data, this is the maximum precision. For character data, this is the length in characters. * For datetime datatypes, this is the length in characters of the String representation (assuming the * maximum allowed precision of the fractional seconds component). For binary data, this is the length in bytes. For the ROWID datatype, * this is the length in bytes. 0 is returned for data types where the * column size is not applicable. * * @param param the first parameter is 1, the second is 2, ... * @return precision * @exception SQLException if a database access error occurs * @since 1.4 */ int getPrecision(int param) throws SQLException; /** * Retrieves the designated parameter's number of digits to right of the decimal point. * 0 is returned for data types where the scale is not applicable. * * @param param the first parameter is 1, the second is 2, ... * @return scale * @exception SQLException if a database access error occurs * @since 1.4 */ int getScale(int param) throws SQLException; /** * Retrieves the designated parameter's SQL type. * * @param param the first parameter is 1, the second is 2, ... * @return SQL type from <code>java.sql.Types</code> * @exception SQLException if a database access error occurs * @since 1.4 * @see Types */ int getParameterType(int param) throws SQLException; /** * Retrieves the designated parameter's database-specific type name. * * @param param the first parameter is 1, the second is 2, ... * @return type the name used by the database. If the parameter type is * a user-defined type, then a fully-qualified type name is returned. * @exception SQLException if a database access error occurs * @since 1.4 */ String getParameterTypeName(int param) throws SQLException; /** * Retrieves the fully-qualified name of the Java class whose instances * should be passed to the method <code>PreparedStatement.setObject</code>. * * @param param the first parameter is 1, the second is 2, ... * @return the fully-qualified name of the class in the Java programming * language that would be used by the method * <code>PreparedStatement.setObject</code> to set the value * in the specified parameter. This is the class name used * for custom mapping. * @exception SQLException if a database access error occurs * @since 1.4 */ String getParameterClassName(int param) throws SQLException; /** * The constant indicating that the mode of the parameter is unknown. */ int parameterModeUnknown = 0; /** * The constant indicating that the parameter's mode is IN. */ int parameterModeIn = 1; /** * The constant indicating that the parameter's mode is INOUT. */ int parameterModeInOut = 2; /** * The constant indicating that the parameter's mode is OUT. */ int parameterModeOut = 4; /** * Retrieves the designated parameter's mode. * * @param param the first parameter is 1, the second is 2, ... * @return mode of the parameter; one of * <code>ParameterMetaData.parameterModeIn</code>, * <code>ParameterMetaData.parameterModeOut</code>, or * <code>ParameterMetaData.parameterModeInOut</code> * <code>ParameterMetaData.parameterModeUnknown</code>. * @exception SQLException if a database access error occurs * @since 1.4 */ int getParameterMode(int param) throws SQLException;}ParameterMetaDatat提供了getParameterCount、getParameterType、getParameterTypeName、getParameterClassName、getParameterMode
com.mysql.jdbc.PreparedStatement
com/mysql/jdbc/PreparedStatement.java
public class PreparedStatement extends com.mysql.jdbc.StatementImpl implements java.sql.PreparedStatement { //...... protected int parameterCount; protected MysqlParameterMetadata parameterMetaData; private InputStream[] parameterStreams = null; private byte[][] parameterValues = null; /** * Only used by statement interceptors at the moment to * provide introspection of bound values */ protected int[] parameterTypes = null; public ParameterBindings getParameterBindings() throws SQLException { synchronized (checkClosed()) { return new EmulatedPreparedStatementBindings(); } } //......} mysql的PreparedStatement实现定义了parameterCount、parameterMetaData、parameterStreams、parameterValues、parameterTypes属性，提供了getParameterBindings办法，返回的是EmulatedPreparedStatementBindings
ParameterBindings
com/mysql/jdbc/ParameterBindings.java
public interface ParameterBindings { public abstract Array getArray(int parameterIndex) throws SQLException; public abstract InputStream getAsciiStream(int parameterIndex) throws SQLException; public abstract BigDecimal getBigDecimal(int parameterIndex) throws SQLException; public abstract InputStream getBinaryStream(int parameterIndex) throws SQLException; public abstract java.sql.Blob getBlob(int parameterIndex) throws SQLException; public abstract boolean getBoolean(int parameterIndex) throws SQLException; public abstract byte getByte(int parameterIndex) throws SQLException; public abstract byte[] getBytes(int parameterIndex) throws SQLException; public abstract Reader getCharacterStream(int parameterIndex) throws SQLException; public abstract Clob getClob(int parameterIndex) throws SQLException; public abstract Date getDate(int parameterIndex) throws SQLException; public abstract double getDouble(int parameterIndex) throws SQLException; public abstract float getFloat(int parameterIndex) throws SQLException; public abstract int getInt(int parameterIndex) throws SQLException; public abstract long getLong(int parameterIndex) throws SQLException; public abstract Reader getNCharacterStream(int parameterIndex) throws SQLException; public abstract Reader getNClob(int parameterIndex) throws SQLException; public abstract Object getObject(int parameterIndex) throws SQLException; public abstract Ref getRef(int parameterIndex) throws SQLException; public abstract short getShort(int parameterIndex) throws SQLException; public abstract String getString(int parameterIndex) throws SQLException; public abstract Time getTime(int parameterIndex) throws SQLException; public abstract Timestamp getTimestamp(int parameterIndex) throws SQLException; public abstract URL getURL(int parameterIndex) throws SQLException; public abstract boolean isNull(int parameterIndex) throws SQLException;}ParameterBindings定义了一系列的get办法
EmulatedPreparedStatementBindings
class EmulatedPreparedStatementBindings implements ParameterBindings { private ResultSetImpl bindingsAsRs; private boolean[] parameterIsNull; EmulatedPreparedStatementBindings() throws SQLException { List<ResultSetRow> rows = new ArrayList<ResultSetRow>(); parameterIsNull = new boolean[parameterCount]; System .arraycopy(isNull, 0, this.parameterIsNull, 0, parameterCount); byte[][] rowData = new byte[parameterCount][]; Field[] typeMetadata = new Field[parameterCount]; for (int i = 0; i < parameterCount; i++) { if (batchCommandIndex == -1) rowData[i] = getBytesRepresentation(i); else rowData[i] = getBytesRepresentationForBatch(i, batchCommandIndex); int charsetIndex = 0; if (parameterTypes[i] == Types.BINARY || parameterTypes[i] == Types.BLOB) { charsetIndex = 63; } else { try { String mysqlEncodingName = CharsetMapping .getMysqlEncodingForJavaEncoding(connection .getEncoding(), connection); charsetIndex = CharsetMapping .getCharsetIndexForMysqlEncodingName(mysqlEncodingName); } catch (SQLException ex) { throw ex; } catch (RuntimeException ex) { SQLException sqlEx = SQLError.createSQLException(ex.toString(), SQLError.SQL_STATE_ILLEGAL_ARGUMENT, null); sqlEx.initCause(ex); throw sqlEx; } } Field parameterMetadata = new Field(null, "parameter_" + (i + 1), charsetIndex, parameterTypes[i], rowData[i].length); parameterMetadata.setConnection(connection); typeMetadata[i] = parameterMetadata; } rows.add(new ByteArrayRow(rowData, getExceptionInterceptor())); this.bindingsAsRs = new ResultSetImpl(connection.getCatalog(), typeMetadata, new RowDataStatic(rows), connection, null); this.bindingsAsRs.next(); } //...... } EmulatedPreparedStatementBindings实现了ParameterBindings接口，它次要是把参数组装到rowData，而后创立了RowDataStatic，结构ResultSetImpl这个对象来实现
小结
jdbc的PreparedStatement并未提供相应的get参数的办法，只能从driver的实现类去找，比方mysql的PreparedStatement实现提供了getParameterBindings办法，返回的是EmulatedPreparedStatementBindings，能够获取参数