mysql-connector-java-5.1.30.jar


com.mysql.jdbc.ResultSetImpl

public String getString(String columnName) throws SQLException {
		return getString(findColumn(columnName));
}

this.columnLabelToIndex = new TreeMap< String, Integer>(String.CASE_INSENSITIVE_ORDER);
TreeMap key 忽略大小写


public int findColumn(String columnName) throws SQLException {
		synchronized (checkClosed().getConnectionMutex()) {
			Integer index;
	
			if (!this.hasBuiltIndexMapping) {
				buildIndexMapping();
			}
	
			index = this.columnToIndexCache.get(columnName);
	
			if (index != null) {
				return index.intValue() + 1;
			}
	
			index = this.columnLabelToIndex.get(columnName);
	
			if (index == null && this.useColumnNamesInFindColumn) {
				index = this.columnNameToIndex.get(columnName);
			}
			
			if (index == null) {
				index = this.fullColumnNameToIndex.get(columnName);
			}
			
			if (index != null) {
				this.columnToIndexCache.put(columnName, index);
				
				return index.intValue() + 1;
			}
	
			// Try this inefficient way, now
	
			for (int i = 0; i < this.fields.length; i++) {
				if (this.fields[i].getName().equalsIgnoreCase(columnName)) {
					return i + 1;
				} else if (this.fields[i].getFullName()
						.equalsIgnoreCase(columnName)) {
					return i + 1;
				}
			}
	
			throw SQLError.createSQLException(Messages.getString("ResultSet.Column____112")
					+ columnName
					+ Messages.getString("ResultSet.___not_found._113"), //$NON-NLS-1$ //$NON-NLS-2$
					SQLError.SQL_STATE_COLUMN_NOT_FOUND, getExceptionInterceptor());
		}
	}
	
	
	// Builds a hash between column names and their indices for fast retrieval.
	 
	public void buildIndexMapping() throws SQLException {
		int numFields = this.fields.length;
		this.columnLabelToIndex = new TreeMap< String, Integer>(String.CASE_INSENSITIVE_ORDER);
		this.fullColumnNameToIndex = new TreeMap< String, Integer>(String.CASE_INSENSITIVE_ORDER);
		this.columnNameToIndex = new TreeMap< String, Integer>(String.CASE_INSENSITIVE_ORDER);
		
		// We do this in reverse order, so that the 'first' column
		// with a given name ends up as the final mapping in the
		// hashtable...
		//
		// Quoting the JDBC Spec:
		//
		// "Column names used as input to getter
		// methods are case insensitive. When a getter method is called with a
		// column
		// name and several columns have the same name, the value of the first
		// matching column will be returned. "
		//
		for (int i = numFields - 1; i >= 0; i--) {
			Integer index = Integer.valueOf(i);
			String columnName = this.fields[i].getOriginalName();
			String columnLabel = this.fields[i].getName();
			String fullColumnName = this.fields[i].getFullName();

			if (columnLabel != null) {			
				this.columnLabelToIndex.put(columnLabel, index);
			}

			if (fullColumnName != null) {
				this.fullColumnNameToIndex.put(fullColumnName, index);
			}
			
			if (columnName != null) {
				this.columnNameToIndex.put(columnName, index);
			}
		}

		// set the flag to prevent rebuilding...
		this.hasBuiltIndexMapping = true;
	}