vb.net code to print barcode Using Dynamic SQL in Java

Draw PDF 417 in Java Using Dynamic SQL

Using Dynamic SQL
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Listing 8.13 Static SQL mock-up
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SELECT * FROM Category WHERE categoryId IN ('ACTADV','SPORTS','STRATEGY') AND name LIKE ('N%')
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8.5.1 Using Java code
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Coding in Java is a great thing. But when you mix Java and SQL together, you have to take care to craft your code in such a way that it retains clarity. As requirements grow more complex, it will become easy to lose track of where all the pieces are. Let s take a look at a mildly complex example that uses straight JDBC to assemble a Dynamic SQL statement and pass it to the database. Listing 8.14 shows the search criteria that we will use to build our SQL statement.
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Listing 8.14 CategorySearchCriteria.java
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public class CategorySearchCriteria implements Serializable { private String firstLetter; private List categoryIds; // setters and getters }
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Our mildly complex SQL statement will receive an unknown quantity of category IDs from the categoryIds property of the CategorySearchCriteria. This will be used to populate the IN statement. The firstLetter property containing a single alpha character will be provided to perform the search against the first letter of the category name. In this example, our focus is on the JDBC interactions and comparing Dynamic SQL solutions. So, we will not expound on anything outside of that. Listing 8.15 shows how to build the Dynamic SQL using only Java code.
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Listing 8.15 CategorySearchDao.java
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public class CategorySearchDao { public List searchCategory( CategorySearchCriteria categorySearchCriteria) { List retVal = new ArrayList();
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Alternative approaches to Dynamic SQL
try { Connection conn = ConnectionPool.getConnection("MyConnectionPool"); PreparedStatement ps = null; ResultSet rs = null; List valueList = new ArrayList(); StringBuffer sql = new StringBuffer(""); sql.append("SELECT * "); sql.append("FROM Category ");
Gets JDBC resources
Starts building SQL query Starts building
dynamic part if(categorySearchCriteria.getCategoryIds() != null && categorySearchCriteria.getCategoryIds().size() > 0) {
Iterator categoryIdIt = categorySearchCriteria.getCategoryIds().iterator(); sql.append("WHERE "); sql.append("categoryId IN ("); if(categoryIdIt.hasNext()) { Object value = categoryIdIt.next(); valueList.add(value); sql.append(" "); } while(categoryIdIt.hasNext()) { Object value = categoryIdIt.next(); valueList.add(value); sql.append(", "); } sql.append(") "); } if(categorySearchCriteria.getFirstLetter() != null && !categorySearchCriteria.getFirstLetter().trim().equals("")) { Don t forget if(valueList.size() != 0) { the AND! sql.append("AND "); } sql.append("name LIKE ( )"); valueList.add(categorySearchCriteria.getFirstLetter() + "%");
Using Dynamic SQL
} ps = conn.prepareStatement(sql.toString()); Iterator valueListIt = valueList.iterator(); int indexCount = 1; while(valueListIt.hasNext()) { ps.setObject(indexCount,valueListIt.next()); indexCount++; }
Prepares statement and sets parameters
Runs the query
rs = ps.executeQuery();
Iterates through results and builds objects to return while(rs.next()) { Category category = new Category(); category.setCategoryId(rs.getInt("categoryId")); category.setTitle(rs.getString("title")); category.setDescription(rs.getString("description")); category.setParentCategoryId( rs.getInt("parentCategoryId")); category.setSequence(rs.getInt("sequence"));
retVal.add(category); } } catch (SQLException ex) { logger.error(ex.getMessage(), ex.fillInStackTrace()); } finally { if (rs != null) The joy of resource cleanup try { rs.close(); } catch (SQLException ex) {logger.error(ex.getMessage(), ex.fillInStackTrace());} if (ps != null) try { ps.close(); } catch (SQLException ex) {logger.error(ex.getMessage(), ex.fillInStackTrace());} if (conn != null) try { conn.close(); } catch (SQLException ex) {logger.error(ex.getMessage(), ex.fillInStackTrace());} } return retVal; } }
Alternative approaches to Dynamic SQL
When using Java code, you are left to handle all the basic repetitious tasks such as connection retrieval, parameter preparation, result set iteration, and object population over and over again. On top of managing the common tasks, in this example we also deal with the minimal complexity introduced by the need to create an IN statement. To deal with this, a List of parameters is created and populated. Even after writing all the code we are still left with less functionality than would be desired to handle our scenario properly. You may have noticed that the PreparedStatement simply uses setObject to assign the parameters. Ideally we would want to have our types specified, but that requirement would have pushed this code to an unreasonable size. In the end, this code is reminiscent of those activities in children s magazines in which you attempt to find cleverly hidden pictures contained in a larger picture. Here the challenge would be to find the Hidden SQL. In this example, straight JDBC becomes seriously inhibitive. Let s move on to take a look at using a stored procedure for Dynamic SQL.
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