Trail: JDBC(TM) Database Access
Lesson: JDBC Basics

使用存储过程

A stored procedure is a group of SQL statements that form a logical unit and perform a particular task, and they are used to encapsulate a set of operations or queries to execute on a database server. For example, operations on an employee database (hire, fire, promote, lookup) could be coded as stored procedures executed by application code. Stored procedures can be compiled and executed with different parameters and results, and they can have any combination of input, output, and input/output parameters.

Note that stored procedures are supported by most DBMSs, but there is a fair amount of variation in their syntax and capabilities. Consequently, the tutorial contains two classes, StoredProcedureJavaDBSample and StoredProcedureMySQLSample to demonstrate how to create stored procedures in Java DB and MySQL, respectively.

此页面包含以下主题：

Overview of Stored Procedures Examples
Parameter Modes
Creating Stored Procedures in Java DB
Creating Stored Procedure in MySQL
- Creating Stored Procedure in MySQL with SQL Scripts or JDBC API
Calling Stored Procedures in Java DB and MySQL

Overview of Stored Procedures Examples

The examples StoredProcedureJavaDBSample.java and StoredProcedureMySQLSample.java create and call the following stored procedures:

SHOW_SUPPLIERS: Prints a result set that contains the names of coffee suppliers and the coffees they supply to The Coffee Break. This stored procedure does not require any parameters. When the example calls this stored procedure, the example produces output similar to the following:
```
Acme, Inc.: Colombian_Decaf
Acme, Inc.: Colombian
Superior Coffee: French_Roast_Decaf
Superior Coffee: French_Roast
The High Ground: Espresso
```
GET_SUPPLIER_OF_COFFEE: Prints the name of the supplier supplierName for the coffee coffeeName. It requires the following parameters:
- IN coffeeName varchar(32): The name of the coffee
- OUT supplierName varchar(40): The name of the coffee supplier
When the example calls this stored procedure with Colombian as the value for coffeeName, the example produces output similar to the following:
```
Supplier of the coffee Colombian: Acme, Inc.
```
RAISE_PRICE: Raises the price of the coffee coffeeName to the price newPrice. If the price increase is greater than the percentage maximumPercentage, then the price is raised by that percentage. This procedure will not change the price if the price newPrice is lower than the original price of the coffee. It requires the following parameters:
- IN coffeeName varchar(32): The name of the coffee
- IN maximumPercentage float: The maximum percentage to raise the coffee's price
- INOUT newPrice numeric(10,2): The new price of the coffee. After the RAISE_PRICE stored procedure has been called, this parameter will contain the current price of the coffee coffeeName.
When the example calls this stored procedure with Colombian as the value for coffeeName, 0.10 as the value for maximumPercentage, and 19.99 as the value for newPrice, the example produces output similar to the following:
```
Contents of COFFEES table before calling RAISE_PRICE:
Colombian, 101, 7.99, 0, 0
Colombian_Decaf, 101, 8.99, 0, 0
Espresso, 150, 9.99, 0, 0
French_Roast, 49, 8.99, 0, 0
French_Roast_Decaf, 49, 9.99, 0, 0

Calling the procedure RAISE_PRICE

Value of newPrice after calling RAISE_PRICE: 8.79

Contents of COFFEES table after calling RAISE_PRICE:
Colombian, 101, 8.79, 0, 0
Colombian_Decaf, 101, 8.99, 0, 0
Espresso, 150, 9.99, 0, 0
French_Roast, 49, 8.99, 0, 0
French_Roast_Decaf, 49, 9.99, 0, 0
```

Parameter Modes

The parameter attributes IN (the default), OUT, and INOUT are parameter modes. They define the action of formal parameters. The following table summarizes the information about parameter modes.

Characteristic of Parameter Mode	IN	OUT	INOUT
Must it be specified in the stored procedure definition?	No; if omitted, then the parameter mode of the formal parameter is `IN`.	Must be specified.	Must be specified.
Does the parameter pass a value to the stored procedure or return a value?	Passes values to a stored procedure.	Returns values to the caller.	Both; passes initial values to a stored procedure; returns updated values to the caller.
Does the formal parameter act as a constant or a variable in the stored procedure?	Formal parameter acts like a constant.	Formal parameter acts like an uninitialized variable.	Formal parameter acts like an initialized variable.
Can the formal parameter be assigned a value in the stored procedure?	Formal parameter cannot be assigned a value.	Formal parameter cannot be used in an expression; must be assigned a value.	Formal parameter must be assigned a value.
What kinds of actual parameters (arguments) can be passed to the stored procedure?	Actual parameter can be a constant, initialized variable, literal, or expression.	Actual parameter must be a variable.	Actual parameter must be a variable.

Creating Stored Procedures in Java DB

注意:See the section "CREATE PROCEDURE statement" in Java DB Reference Manual for more information about creating stored procedures in Java DB.

Creating and using a stored procedure in Java DB involves the following steps:

Create a public static Java method in a Java class:This method performs the required task of the stored procedure.
Create the stored procedure:This stored procedure calls the Java method you created.
Package the Java class (that contains the public static Java method you created earlier) in a JAR file.
Call the stored procedure with the CALL SQL statement. See the section Calling Stored Procedures in Java DB and MySQL.

Creating Public Static Java Method

The following method, StoredProcedureJavaDBSample.showSuppliers, contains the SQL statements that the stored procedure SHOW_SUPPLIERS calls:

public static void showSuppliers(ResultSet[] rs)
    throws SQLException {

    Connection con = DriverManager.getConnection("jdbc:default:connection");
    Statement stmt = null;

    String query =
        "select SUPPLIERS.SUP_NAME, " +
        "COFFEES.COF_NAME " +
        "from SUPPLIERS, COFFEES " +
        "where SUPPLIERS.SUP_ID = " +
        "COFFEES.SUP_ID " +
        "order by SUP_NAME";

    stmt = con.createStatement();
    rs[0] = stmt.executeQuery(query);
}

The SHOW_SUPPLIERS stored procedure takes no arguments. You can specify arguments in a stored procedure by defining them in the method signature of your public static Java method. Note that the method showSuppliers contains a parameter of type ResultSet[]. If your stored procedure returns any number of ResultSet objects, specify one parameter of type ResultSet[] in your Java method. In addition, ensure that this Java method is public and static.

Retrieve the Connection object from the URL jdbc:default:connection. This is a convention in Java DB to indicate that the stored procedure will use the currently existing Connection object.

Note that the Statement object is not closed in this method. Do not close any Statement objects in the Java method of your stored procedure; if you do so, the ResultSet object will not exist when you issue the CALL statement when you call your stored procedure.

In order for the stored procedure to return a generated result set, you must assign the result set to an array component of the ResultSet[] parameter. In this example, the generated result set is assigned to the array component rs[0].

The following method is StoredProcedureJavaDBSample.showSuppliers:

public static void getSupplierOfCoffee(String coffeeName, String[] supplierName)
    throws SQLException {

    Connection con = DriverManager.getConnection("jdbc:default:connection");
    PreparedStatement pstmt = null;
    ResultSet rs = null;

    String query =
        "select SUPPLIERS.SUP_NAME " +
        "from SUPPLIERS, COFFEES " +
        "where " +
        "SUPPLIERS.SUP_ID = COFFEES.SUP_ID " +
        "and ? = COFFEES.COF_NAME";

    pstmt = con.prepareStatement(query);
    pstmt.setString(1, coffeeName);
    rs = pstmt.executeQuery();

    if (rs.next()) {
        supplierName[0] = rs.getString(1);
    } else {
        supplierName[0] = null;
    }
}

The formal parameter coffeeName has the parameter mode IN. This formal parameter is used like any other parameter in a Java method. Because the formal parameter supplierName has the parameter mode OUT, it must use a one dimensional array data type. Because this method does not produce a result set, the method definition does not contain a parameter of type ResultSet[]. In order to retrieve a value from an OUT formal parameter, you must assign the value to be retrieved to an array component of the OUT formal parameter. In this example, the retrieved name of the coffee supplier is assigned to the array component supplierName[0].

The following is the method signature of the StoredProcedureJavaDBSample.raisePrice method:

public static void raisePrice(
   String coffeeName, double maximumPercentage,
   BigDecimal[] newPrice) throws SQLException

Because the formal parameter newPrice has the parameter mode INOUT, it must use a one dimensional array data type. Java DB maps the FLOAT and NUMERIC SQL data types to the double and java.math.BigDecimal Java data types, respectively.

Creating Stored Procedures in Java DB with SQL Scripts or JDBC API

Java DB uses the Java programming language for its stored procedures. Consequently, when you define a stored procedure, you specify which Java class to call and where Java DB can find it.

The following excerpt from StoredProcedureJavaDBSample.createProcedures creates a stored procedure named SHOW_SUPPLIERS:

public void createProcedures(Connection con)
    throws SQLException {

    Statement stmtCreateShowSuppliers = null;

    // ...

    String queryShowSuppliers =
        "CREATE PROCEDURE SHOW_SUPPLIERS() " +
        "PARAMETER STYLE JAVA " +
        "LANGUAGE JAVA " +
        "DYNAMIC RESULT SETS 1 " +
        "EXTERNAL NAME " +
        "'com.oracle.tutorial.jdbc." +
        "StoredProcedureJavaDBSample." +
        "showSuppliers'";

    // ...

    try {
        System.out.println("Calling CREATE PROCEDURE");
        stmtCreateShowSuppliers = con.createStatement();

        // ...

    } catch (SQLException e) {
        JDBCTutorialUtilities.printSQLException(e);
    } finally {
        if (stmtCreateShowSuppliers != null) {
            stmtCreateShowSuppliers.close();
        }
        // ...
    }
}

The following list describes the procedure elements you can specify in the CREATE PROCEDURE statement:

PARAMETER STYLE: Identifies the convention used to pass parameters to the stored procedure. The following options are valid:
- JAVA: Specifies that the stored procedure uses a parameter-passing convention that conforms to the Java language and the SQL routines specification.
- DERBY: Specifies that the stored procedure supports a vararg as the final argument in the parameter list.
LANGUAGE JAVA: Specifies the programming language of the stored procedure (currently, JAVA is the only option).
DYNAMIC RESULT SETS 1: Specifies the maximum number of result sets retrieved; in this case, it is 1.
EXTERNAL NAME 'com.oracle.tutorial.jdbc.StoredProcedureJavaDBSample.showSuppliers' specifies the fully qualified Java method that this stored procedure calls. 注意:Java DB must be able to find the method specified here in your class path or in a JAR file directly added to the database. See the following step, Package Java Class in JAR File.

The following statement (which is found in StoredProcedureJavaDBSample.createProcedures) creates a stored procedure named GET_SUPPLIERS_OF_COFFEE (line breaks have been added for clarity):

CREATE PROCEDURE GET_SUPPLIER_OF_COFFEE(
    IN coffeeName varchar(32),
    OUT supplierName
    varchar(40))
    PARAMETER STYLE JAVA
    LANGUAGE JAVA
    DYNAMIC RESULT SETS 0
    EXTERNAL NAME 'com.oracle.tutorial.jdbc.
        StoredProcedureJavaDBSample.
        getSupplierOfCoffee'

This stored procedure has two formal parameters, coffeeName and supplierName. The parameter specifiers IN and OUT are called parameter modes. They define the action of formal parameters. See Parameter Modes for more information. This stored procedure does not retrieve a result set, so the procedure element DYNAMIC RESULT SETS is 0.

The following statement creates a stored procedure named RAISE_PRICE (line breaks have been added for clarity):

CREATE PROCEDURE RAISE_PRICE(
    IN coffeeName varchar(32),
    IN maximumPercentage float,
    INOUT newPrice float)
    PARAMETER STYLE JAVA
    LANGUAGE JAVA
    DYNAMIC RESULT SETS 0
    EXTERNAL NAME 'com.oracle.tutorial.jdbc.
        StoredProcedureJavaDBSample.raisePrice'

You can use SQL scripts to create stored procedures in Java DB. See the script javadb/create-procedures.sql and the Ant target javadb-create-procedure in the build.xml Ant build script.

Package Java Class in JAR File

The Ant build script build.xml contains targets to compile and package the tutorial in a JAR file. At a command prompt, change the current directory to <JDBC tutorial directory>. From this directory, run the following command to compile and package the tutorial in a JAR file:

ant jar

The name of the JAR file is <JDBC tutorial directory>/lib/JDBCTutorial.jar.

The Ant build script adds the file JDBCTutorial.jar to the class path. You can also specify the location of the JAR file in your CLASSPATH environment variable. This enables Java DB to find the Java method that the stored procedure calls.

Adding JAR File Directly to Database

Java DB looks first in your class path for any required classes, and then in the database. This section shows you how to add JAR files directly to the database.

Use the following system procedures to add the JDBCTutorial.jar JAR file to the database (line breaks have been added for clarity):

CALL sqlj.install_jar(
  '<JDBC tutorial directory>/
  lib/JDBCTutorial.jar',
  'APP.JDBCTutorial', 0)
CALL sqlj.replace_jar(
  '<JDBC tutorial directory>/
  lib/JDBCTutorial.jar',
  'APP.JDBCTutorial')";
CALL syscs_util.syscs_set_database_property(
  'derby.database.classpath',
  'APP.JDBCTutorial')";

注意:The method StoredProcedureJavaDBSample.registerJarFile demonstrates how to call these system procedures. If you call this method, ensure that you have modified javadb-sample-properties.xml so that the value of the property jar_file is set to the full path name of JDBCTutorial.jar.

The install_jar procedure in the SQL schema adds a JAR file to the database. The first argument of this procedure is the full path name of the JAR file on the computer from which this procedure is run. The second argument is an identifier that Java DB uses to refer to the JAR file. (The identifier APP is the Java DB default schema.) The replace_jar procedure replaces a JAR file already in the database.

The system procedure SYSCS_UTIL.SYSCS_SET_DATABASE_PROPERTY sets or deletes the value of a property of the database on the current connection. This method sets the property derby.database.classpath to the identifier specified in the install_jar file. Java DB first looks in your Java class path for a class, then it looks in derby.database.classpath.

Creating Stored Procedure in MySQL

Creating and using a stored procedure in Java DB involves the following steps:

Create the stored procedure with an SQL script or JDBC API
Call the stored procedure with the CALL SQL statement. See the section Calling Stored Procedures in Java DB and MySQL

Creating Stored Procedure in MySQL with SQL Scripts or JDBC API

MySQL uses a SQL-based syntax for its stored procedures. The following excerpt from the SQL script mysql/create-procedures.sql creates a stored procedure named SHOW_SUPPLIERS:

SELECT 'Dropping procedure SHOW_SUPPLIERS' AS ' '|
drop procedure if exists SHOW_SUPPLIERS|

# ...

SELECT 'Creating procedure SHOW_SUPPLIERS' AS ' '|
create procedure SHOW_SUPPLIERS()
    begin
        select SUPPLIERS.SUP_NAME,
        COFFEES.COF_NAME
        from SUPPLIERS, COFFEES
        where SUPPLIERS.SUP_ID = COFFEES.SUP_ID
        order by SUP_NAME;
    end|

The DROP PROCEDURE statement deletes that procedure SHOW_SUPPLIERS if it exists. In MySQL, statements in a stored procedure are separated by semicolons. However, a different delimiter is required to end the create procedure statement. This example uses the pipe (|) character; you can use another character (or more than one character). This character that separates statements is defined in the delimiter attribute in the Ant target that calls this script. This excerpt is from the Ant build file build.xml (line breaks have been inserted for clarity):

<target name="mysql-create-procedure">

  <sql driver="${DB.DRIVER}"
       url="${DB.URL}" userid="${DB.USER}"
       password="${DB.PASSWORD}"
       classpathref="CLASSPATH"
       print="true"
       delimiter="|"
       autocommit="false"
       onerror="abort">
       <transaction
         src="./sql/${DB.VENDOR}/
           create-procedures.sql">
       </transaction>
  </sql>

</target>

Alternatively, you can use the DELIMITER SQL statement to specify a different delimiter character.

The CREATE PROCEDURE statement consists of the name of the procedure, a comma-separated list of parameters in parentheses, and SQL statements within the BEGIN and END keywords.

You can use the JDBC API to create a stored procedure. The following method, StoredProcedureMySQLSample.createProcedureShowSuppliers, performs the same tasks as the previous script:

public void
    createProcedureShowSuppliers()
    throws SQLException {
    String createProcedure = null;

    String queryDrop =
        "DROP PROCEDURE IF EXISTS SHOW_SUPPLIERS";

    createProcedure =
        "create procedure SHOW_SUPPLIERS() " +
        "begin " +
            "select SUPPLIERS.SUP_NAME, " +
            "COFFEES.COF_NAME " +
            "from SUPPLIERS, COFFEES " +
            "where SUPPLIERS.SUP_ID = " +
            "COFFEES.SUP_ID " +
            "order by SUP_NAME; " +
        "end";
    Statement stmt = null;
    Statement stmtDrop = null;

    try {
        System.out.println("Calling DROP PROCEDURE");
        stmtDrop = con.createStatement();
        stmtDrop.execute(queryDrop);
    } catch (SQLException e) {
        JDBCTutorialUtilities.printSQLException(e);
    } finally {
        if (stmtDrop != null)
        {
            stmtDrop.close();
        }
    }

    try {
        stmt = con.createStatement();
        stmt.executeUpdate(createProcedure);
    } catch (SQLException e) {
        JDBCTutorialUtilities.printSQLException(e);
    } finally {
        if (stmt != null) { stmt.close(); }
    }
}

Note that the delimiter has not been changed in this method.

The stored procedure SHOW_SUPPLIERS generates a result set, even though the return type of the method createProcedureShowSuppliers is void and the method does not contain any parameters. A result set is returned when the stored procedure SHOW_SUPPLIERS is called with the method CallableStatement.executeQuery:

CallableStatement cs = null;
cs = this.con.prepareCall("{call SHOW_SUPPLIERS}");
ResultSet rs = cs.executeQuery();

The following excerpt from the method StoredProcedureMySQLSample.createProcedureGetSupplierOfCoffee contains the SQL query that creates a stored procedure named GET_SUPPLIER_OF_COFFEE:

public void createProcedureGetSupplierOfCoffee()
    throws SQLException {

    String createProcedure = null;

    // ...

    createProcedure =
        "create procedure GET_SUPPLIER_OF_COFFEE(" +
        "IN coffeeName varchar(32), " +
        "OUT supplierName varchar(40)) " +
        "begin " +
            "select SUPPLIERS.SUP_NAME into " +
            "supplierName " +
            "from SUPPLIERS, COFFEES " +
            "where SUPPLIERS.SUP_ID = " +
            "COFFEES.SUP_ID " +
            "and coffeeName = COFFEES.COF_NAME; " +
            "select supplierName; " +
        "end";
    // ...
}

This stored procedure has two formal parameters, coffeeName and supplierName. The parameter specifiers IN and OUT are called parameter modes. They define the action of formal parameters. See Parameter Modes for more information. The formal parameters are defined in the SQL query, not in the method createProcedureGetSupplierOfCoffee. To assign a value to the OUT parameter supplierName, this stored procedure uses a SELECT statement.

The following excerpt from the method StoredProcedureMySQLSample.createProcedureRaisePrice contains the SQL query that creates a stored procedure named RAISE_PRICE:

public void createProcedureRaisePrice()
    throws SQLException {

    String createProcedure = null;

    // ...

    createProcedure =
        "create procedure RAISE_PRICE(" +
        "IN coffeeName varchar(32), " +
        "IN maximumPercentage float, " +
        "INOUT newPrice numeric(10,2)) " +
        "begin " +
        "main: BEGIN " +
            "declare maximumNewPrice " +
                "numeric(10,2); " +
            "declare oldPrice numeric(10,2); " +
            "select COFFEES.PRICE into oldPrice " +
                "from COFFEES " +
                "where COFFEES.COF_NAME " +
                "= coffeeName; " +
            "set maximumNewPrice = " +
                "oldPrice * (1 + " +
                "maximumPercentage); " +
            "if (newPrice > maximumNewPrice) " +
                "then set newPrice = " +
                "maximumNewPrice; " +
            "end if; " +
            "if (newPrice <= oldPrice) " +
                "then set newPrice = oldPrice; " +
                "leave main; " +
            "end if; " +
            "update COFFEES " +
                "set COFFEES.PRICE = newPrice " +
                "where COFFEES.COF_NAME " +
                "= coffeeName; " +
            "select newPrice; " +
        "END main; " +
        "end";

    // ...
}

The stored procedure assigns a value to the INOUT parameter newPrice with the SET and SELECT statements. To exit the stored procedure, the stored procedure first encloses the statements in a BEGIN ... END block labeled main. To exit the procedure, the method uses the statement leave main.

Calling Stored Procedures in Java DB and MySQL

The following excerpt from method runStoredProcedures, calls the stored procedure SHOW_SUPPLIERS and prints the generated result set:

cs = this.con.prepareCall("{call SHOW_SUPPLIERS()}");
ResultSet rs = cs.executeQuery();

while (rs.next()) {
    String supplier = rs.getString("SUP_NAME");
    String coffee = rs.getString("COF_NAME");
    System.out.println(supplier + ": " + coffee);
}

注意:As with Statement objects, to call the stored procedure, you can call execute, executeQuery, or executeUpdate depending on how many ResultSet objects the procedure returns. However, if you are not sure how many ResultSet objects the procedure returns, call execute.

Calling the stored procedure SHOW_SUPPLIERS is demonstrated in the section Creating Stored Procedure with JDBC API in MySQL.

The following excerpt from method runStoredProcedures, calls the stored procedure GET_SUPPLIER_OF_COFFEE:

cs = this.con.prepareCall("{call GET_SUPPLIER_OF_COFFEE(?, ?)}");
cs.setString(1, coffeeNameArg);
cs.registerOutParameter(2, Types.VARCHAR);
cs.executeQuery();

String supplierName = cs.getString(2);

The interface CallableStatement extends PreparedStatement. It is used to call stored procedures. Specify values for IN parameters (such as coffeeName in this example) just like you would with a PreparedStatement object by calling the appropriate setter method. However, if a stored procedure contains an OUT parameter, you must register it with the registerOutParameter method.

The following excerpt from the method runStoredProcedures, calls the stored procedure RAISE_PRICE:

cs = this.con.prepareCall("{call RAISE_PRICE(?,?,?)}");
cs.setString(1, coffeeNameArg);
cs.setFloat(2, maximumPercentageArg);
cs.registerOutParameter(3, Types.NUMERIC);
cs.setFloat(3, newPriceArg);

cs.execute();

Because the parameter newPrice (the third parameter in the procedure RAISE_PRICE) has the parameter mode INOUT, you must both specify its value by calling the appropriate setter method and register it with the registerOutParameter method.