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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
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